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1. What is the limit of frequency up to which signals using a sky wave can be transmitted?
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2. Draw the graph showing the variation of See beck coefficient with temperature of the hot junction.
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3. What is the power factor of an LCR series a.c. circuit at resonance?
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4. The binding energy per nucleon for two nuclei A, B is given as 4 MeV and 8.5 MeV. Which of the two nuclei is more stable?
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5. Why is the energy of the electron emitted during beta decay continuous?
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6. “The magnetic lines of force prefer to pass through iron than air.” Give reason,
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7. The surface temperatures of two stars are in the ratio 1: 2. What is the ratio of the energy radiated by them per second?
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8. Two point charges 5 µC and 10 µC are separated by a distance V in air. If an additional charge of - 4 µC is given to each, by what factor does the force between the charges change?
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9. Explain briefly, with a ray diagram, how a mirage is formed in deserts.
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10. A wire of 5 ohm resistance is stretched to twice its original length. What will be its (0 new resistivity, and (ii) new resistance?
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11. The following circuit shows the use of potentiometer to measure the internal resistance of a cell:
(i) When the key K is open, how does the balance point change, if the current from the driver cell decreases?
(ii) When the key K is closed, how does the balance point change if R is increased, keeping the current from the driver cell constant?
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12. Three identical resistors when connected in series to a d.c. source, dissipate a power X watts. If these resistors are connected in parallel to the same d.c. source, what will be the power dissipation in this case?
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13. Draw energy band diagrams of (i) n-type, and (ii) /Hype semiconductors.
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14. A proton, placed in a uniform electric field of magnitude 103 NC-1, moves from a point A to B in the direction of electric field. If AB = 0.1 m, calculate the
(i) potential difference between A and B, and (ii) work done in moving the proton from A to B.
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15. An air-core solenoid is connected to an a.c. source and a bulb. If an iron-core is inserted in the solenoid, how does the brightness of the bulb change? Give reason for your answer.
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16. A small light source having uniform luminous intensity of 10 candela is situated at the centre of a spherical surface of radius 1 m. Calculate (0 the luminous flux, and (ii) illuminance on the spherical surface.
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17. Write, in brief, the method to determine the distance of an inferior planet from the earth.
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18. A circular coil of 30 turns and radius 8.0 cm carrying a current of 6.0 A is suspended vertically in a uniform horizontal magnetic field of magnitude 1.0 T. The field lines make an angle of 60° with the normal to the coil. Calculate the magnitude of counter torque that must be applied to prevent the coil from turning.
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19. If the frequency of incident radiation on a photo-cell is doubled for the same intensity, what changes will you observe in
(0 the kinetic energy of photo-electrons emitted Hi) photo-electric current, and (lit) stopping potential?
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20. Write the expression for magnetic dipole moment for a closed current loop. Give its S.I. unit.
Derive the expression for the torque experienced by a magnetic dipole in a uniform magnetic field.
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21. A battery of emf, E and internal resistance V, gives a current of 0.4 A with an external resistor of 12 ohm, and a current of 0.25 A with an external resistor of 20 ohm. Calculate (i) internal resistance and (ii) emf of the battery.
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22. Two long parallel metallic wires carrying electric current in the opposite directions repel each other. Why? Derive the expression for the force experienced in this case.
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23. When the solar spectrum is observed by means of a spectroscope, a number of dark lines crossing the spectrum are observed. What are these lines called? What is their origin? What information is obtained by studying these lines?
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24. Sketch the graph showing the variation of intensity of transmitted light on the angle of rotation between a polarizer and analyser. A ray of light is incident at an angle of incidence ip on the surface of separation between air and a medium of refractive index µ, such that the angle between the reflected and refracted rays is 90°. Obtain the relation between ip and µ.
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25. A parallel beam of light is incident on an air-glass interface. Using Huygen’ sprinciple and drawing the sketches of wave fronts, show how the wave is refracted and hence verify law of refraction.
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26. Write the truth table of a 2-input NOR gate. Explain, using a logic circuit, how a NOR gate can be converted into an AND gate.
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27. Explain the use oip-n junction diode as a rectifier. Draw the circuit diagram of a full wave rectifier. Explain its working giving its input and output wave forms.
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28. Derive an expression for the energy stored in a parallel plate capacitor. Hence show that electric field E itself is a source of energy with energy density
½ ε0 E2 Jm-3
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29. (a) State Bohr’s postulates for hydrogen atom.
(b) Draw the energy diagram showing the ground state, and the next few excited states for hydrogen (H2) atom. Mark the transition which corresponds to the emission of spectral lines for the B aimer-series.
© Calculate the wavelength of the first spectral line in this series.
Answer
30. (a) Write the principle on which an a.c. generator works. Draw its labelled diagram.
(b) An ax. generator consists of a coil of 50 turns and area 2.5 m2 rotating at an angular speed of 60 rad s-1 in a uniform magnetic field B = 0.2 T between the two fixed pole pieces. The resistance of the circuit including that of the coil is 500 ohm.
(i) Calculate the maximum current drawn from the generator.
(ii) What is the flux when the current is zero?
(iii) Would the generator work if the coil were stationary and instead the pole pieces rotated together with the same speed as above? Give reason.
Or
Explain, with the help of a labelled diagram, the working principle uf a step up transformer.
The primary of a transformer has 200 turns and the secondary has 1000 turns. If the power output from the secondary at 1000 V is 9 kW, calculate (0 the primary voltage, and
(ii) the heat loss in the primary coil if the resistance of primary is 0.2 ohm and the efficiency of the transformer is 90%.
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Q. 1. Sketch two equipotential surfaces for a point charge.
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Q. 2. If the length of a wire conductor is doubled by stretching it, keeping the p.d. across it constant, by what factor does the drift speed of electrons change?
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Q. 3. Give two factors on which the temperature of inversion of a thermocouple depends.
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Q. 4. The current through the wire PQ is increasing. In which direction does the induced current flow in the closed loop?
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Q. 5. What is the range of frequencies used for TV transmission?
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Q. 6. Sketch the refracted wave front emerging from a convex lens, if a plane wave front is incident normally on it.
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Q. 7. Why do magnetic lines of force prefer to pass through fer¬romagnetic substances than through air?
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Q. 8. Two stars A and B have their magnitudes - 3 and + 5 respec¬tively. Which star looks brighter?
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Q. 9. (i) Calculate the electric potential at a point X due to a charge of 0.5 μC located at 10 cm from it.
(ii) Also calculate the work done in bringing a charge of 3 x 10-9 C from infinity to the point X.
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Q. 10. Draw a labelled diagram of a Lechlanche cell. How is polarisation overcome in this cell?
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Q. 11. With the help of a circuit diagram explain how a silver voltameter can be used to check the accuracy of an ammeter.
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Q. 12. How are eddy currents produced? Mention two applications of eddy currents.
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Q. 13. In a plane electromagnetic wave, the electric field oscillates with a frequency of 2 x 1010 s-1 and an amplitude of 40 V/m.
(i) What is the wavelength of the wave, and
(ii) What is the energy density due to the electric field?
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Q. 14. The aperture of the objective lens of an astronomical telescope is doubled. How does it affect
(i) the resolving power of the telescope, and (ii) the intensity of the image ?
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Q. 15. An illuminance of 2 x 105 lumen/m2 is produced by sunlight incident normally on the surface of the earth. Calculate the luminous flux of the sun, if it is at a mean distance of 1.5 x 1011 m from the earth.
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Q. 16. What is an ideal diode? Draw the output wave form across the load resistance R, if the input wave form is as shown in the figure.
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Q. 17. The activity of a radioactive element drops to 1/16th of its initial, value in 32 years. Find the mean life of the sample.
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Q. 18. Describe how the distance of an inferior planet from the sun can be determined?
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Q. 19. Define resistivity of a substance. Give its unit. How does it vary with temperature in
(i) good conductors,
(ii) ionic conductors, and
(iii) semiconductors?
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Q. 20. How will you use a meter bridge to measure an unknown resistance? Draw the necessary circuit diagram. Explain the principle of the experiment. Give the formula used.
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Q. 21. Explain how you will convert a galvanometer into a voltmeter to read a maximum potential of ‘V’ volts. Can one use a voltmeter to measure the e.m.f. of a cell? Justify your answer.
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Q. 22. How does the angle of dip vary as one moves from the Equator towards the North Pole? If the horizontal component of earth’s magnetic field at a place where the angle of dip is 60° is 0.4 x 10-4 tesla, calculate the vertical component and the resultant magnetic field of earth at that point.
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Q. 23. Derive the expression for the fringe width in Young’s double slit experiment, for a monochromatic source of light.
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Q. 24. A compound lens is made of two lenses in contact having powers + 12.5 D and - 2.5 D. An object is placed at 15 cm from this compound lens. Find the position and nature of the image formed.
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Q. 25. Draw a labelled diagram of Millikan’s oil drop experiment. Discuss the principle involved in the determination of the electronic charge.
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Q. 26. The output of a 2-input AND gate is fed to a NOT gate. Draw the logic circuit of the combination and write down the truth table. Identify the new logic gate formed.
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Q. 27. Draw a circuit diagram to show the biasing of an n-p-n transistor. Explain the transistor action.
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Q. 28. Prove that an ideal capacitor does not dissipate power in an a.c. circuit.
Find the inductance of the inductor used in series with a bulb of resistance 10 ohm connected to an a.c source of 80 V, 50 Hz. The power factor of the circuit is 0.5. Also, calculate the power dissipation in the circuit.
Answer
Q. 29. Explain the principle, construction and working of a Van de Graff generator.
Or
Derive the expression for the capacitance of a parallel plate capacitor when the space between the plates is partially filled with a dielectric medium of dielectric constant ‘K’ Explain why the capacitance decreases when the dielectric medium is removed from between the plates.
Answer
Q. 30. State Bohr’s postulates for hydrogen atom.
The wavelength of the first spectral line of Balmer series in hydrogen spectrum is 6560 A. Calculate the wavelength of the 2nd spectral line of Lyman series, lonisation energy of hydrogen atom is 13.6 eV.
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Q. 1. Give the ratio of velocities of light rays of wavelengths 4000 A and 8000 A in vacuum.
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Q. 2. A student obtains resistances of 3, 4, 12 and 16 ohms using only two metallic resistance wires either separately or joined together. What is the value of resistance of each of these wires?
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Q. 3. Define ‘dielectric constant’ of a medium in terms of force between electric charges.
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Q. 4. The wavelengths of some of the spectral lines obtained in hydrogen spectrum are 9546 A, 6463 k and 1216 A. Which one of these wavelengths belongs to Lyman series?
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Q. 5. Write the truth table for the combination of gates shown here.
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Q. 6. In a certain arrangement a proton does not get deflected while passing through a magnetic field region. Under what condition is it possible?
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Q. 7. Give the phase difference between the applied a.c. voltage and the current in an LCR circuit, at resonance.
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Q. 8. Refractive index of glass for lights of yellow, green and red colours are μy, μg and μr respectively. Rearrange these symbols in an increasing order of values.
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Q. 9. Define ‘intensity of electric field’ at a point. At what points is the electric dipole field intensity parallel to the line joining the charges?
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Q. 10. Capacitors P, Q and R have each a capacity C. A battery can charge the capacitor P to a potential V. If after charging P the battery is disconnected from it and the charged capacitor P is connected in following separate instances to Q and R
(i) to Q in parallel, and
(ii) to R in series ;
then what will be the potential differences between the plates of P in the two instances ?
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Q. 11. Define ‘chemical equivalent’ and ‘electro-chemical equivalent’ of a substance. Establish the relationship between the two.
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Q. 12. State and illustrate Curies law in magnetism.
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Q. 13. How can the magnetic moments of two bar magnets of same size and mass be compared using a vibration magnetometer?
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Q. 14. State Lenz’s law. Show that it is a consequence of the law of conservation of energy.
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Q. 15. Prove mathematically that the average power over a complete cycle of alternating current through an ideal inductor is zero.
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Q. 16. Draw a graph showing the variation of stopping potential with frequency of incident radiations in relation to photoelectric effect. Deduce an expression for the slope of this graph using Einstein’s photoelectric equation.
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Q. 17. Define ‘disintegration constant* and ‘mean life’ of a radioactive substance. Give the unit for each.
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Q. 18. Distinguish between n-type and p-type semi-conductors on the basis of energy-band diagram.
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Q. 19. State Gauss’s theorem. Using Gauss theorem, derive an expression for electric field intensity at any point inside a hollow charged conducting sphere.
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Q. 20. Why is a potentiometer preferred over a voltmeter to measure e.m.f. of a cell? The potentiometer wire AB shown in the figure is 400 cm long. Where should the free end of the galvanometer be connected on AB so that the galvanometer shows zero deflection?
Answer
Q. 21. A potential difference V is applied across a conductor of length L and diameter D. How are the electric field E and the resistance R of conductor affected when in turn
(i) V is halved,
(ii) L is halved and
(Hi) D is doubled?
Justify your answer in each case.
Answer
Q. 22. When an alternating voltage of 220 V is applied across a device X, a current of 0.5 A flows through the circuit and is in phase with the applied voltage. When the same voltage is applied across another device Y, the same current again flows through the circuit but it leads the applied voltage by π/2 radians.
(a) Name the devices X and Y.
(b) Calculate the current flowing in the circuit when same voltage is applied across the series combination of X and Y.
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Q. 23. Derive the expression for the fringe width in Young’s double slit interference experiment.
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Q. 24. What is Doppler effect in light? The spectral line for a given element in light received from a distant star is shifted towards longer wavelength by 0.025%. Calculate the velocity of star in the line of sight.
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Q. 25. Draw a labelled ray diagram for a refracting type astronomical telescope. How will its magnifying power be affected on increasing for its eye-piece (i) the focal length, and (ii) the aperture? Justify your answer.
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Q. 26. Establish the relationship between the object distance, image distance and radius of curvature for a convex mirror.
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Q. 27. Define ’solar constant’. Derive an expression for surface temperature of the sun in terms of solar constant and solar radius.
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Q. 28. Explain with the help of a labelled diagram, the underlying principle, construction and working of a moving coil galvanometer.
Or
Explain with the help of a labelled diagram, the underlying principle, construction and working of a cyclotron.
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Q. 29. State Bohr’s postulates. Using these postulates derive an ex¬pression for the total energy of an electron in the nth orbit of an atom. What does negative value of this energy signify?
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Q. 30. Explain, with the help of a labelled circuit diagram the use of NPN transistor as an amplifier hi common emitter configuration. Why is a common emitter amplifier preferred over common base amplifier?
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Q. 1. In a medium the force of attraction between two point electric charges, distance’d’ apart, is F. What distance apart should these be kept in the same medium so that the force between them becomes 3F?
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Q. 2. Name the experiment which established the quantum nature of electric charges.
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Q. 3. Draw energy-band diagram of a p-type extrinsic semiconductor.
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Q. 4. An electron and proton moving with the same speed enter the same magnetic field region at right angles to the direction of the field. For which of the two particles will the radius of the circular path be smaller?
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Q. 5. Two electric bulbs A and B are marked 220 V, 60 W and 220 V, 100 W respectively. Which one of the two has greater resistance?
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Q. 6. An ideal inductor is in turn put across 220 V, 50 Hz and 220 V, 100 Hz supplies. Will the current flowing through it in the two cases be the same or different?
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Q. 7. Write the following radiations in an ascending order in respect of their frequencies:
X-rays, micro-waves, ultraviolet rays and radio waves.
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Q. 8. Write the truth table for the following combination of gates:
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Q. 9. Two identical point charges of charge ‘£»’ are kept at a distance V* from each other. A third point charge is placed on the line joining the above two charges such that all the three charges are in equilibrium. Calculate the magnitude and location of the third charge.
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Q. 10. When a capacitor is connected in series with a series L-R circuit, the alternating current flowing in the circuit increases. Explain why?
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Q. 11. V-l graph for a metallic wire at two different temperatures T1 and T2 is as shown in the following figure. Which of the two temperatures T1 and T2 is higher and why?
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Q. 12. Explain the principle on which the working of a potentiometer is based. Why is the use of a potentiometer preferred over that of a voltmeter for measurement of emf of a cell?
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Q. 13. State the working principle of a tangent galvanometer. Write the mathematical expression for measuring currents using the tangent galvanometer.
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Q. 14. You are given two identical looking bars A and B. One of these is a bar magnet and the other an ordinary piece of iron- Give an experiment to identify which one of the two is a bar magnet. You are not to use any additional materials for experiment.
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Q. 15. Define the terms ‘luminous flux’ and ‘luminous intensity’. How are these two related to each other?
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Q. 16. How does the (i) magnifying power and (ii) resolving power of a telescope change on increasing the diameter of its objective? Give reasons for your answer.
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Q. 17. Explain laws of photoelectric emission on the basis of Einstein’s photoelectric equation.
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Q. 18. Calculate the half life period of a radioactive substance if its activity drops to 1/16th of its initial value in 30 years.
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Q. 19. A potential difference of 2 volt is applied between the points A and B shown in the network drawn in the figure. Calculate:
(i) equivalent resistance of the network across the points A and B, and
(it) the magnitudes of currents flowing in the arms AFCEB and AFDEB.
Answer
Q. 20. The potential difference across the terminals of a battery of emf 12 V and internal resistance 2 Ω drops to 10 V when it is connected to a silver voltmeter. Calculate the silver deposited at the cathode in half an hour. Atomic weight of silver is 107.9 g mole?
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Q. 21. Derive a formula for the force between two parallel straight conductors carrying current in opposite directions and write the nature of the force. Hence, define an ampere.
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Q. 22. What are coherent sources of light? Why is no interference
Pattern observed when two coherent sources are
(1) infinitely close to each other ?
(ii) far apart from each other ?
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Q. 23. A slit of width’d’ is illuminated by light of wavelength 6500 A. For what values of‘d’ will the
(i) first minimum fall at an angle of diffraction of 30°?
(ii) first maximum fall at an angle of diffraction of 30° ?
Answer
Q. 24. Draw a ray diagram to show the formation of the image of an object placed between f and 2f of a thin concave lens. Deduce the relation between the object distance, the image distance and the focal length of the lens under this condition.
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Q. 25. Define the terms ‘potential barrier’ and depletion region’ for a p-n junction diode. State how the thickness of depletion region will change when the p-n junction diode is
(i) forward biased.
(ii) reverse biased ?
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Q. 26. With the help of a labelled circuit diagram, explain the use of a transistor as an oscillator.
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Q. 27. Define ‘absolute magnitude of a star. Assuming that the dimmest star visible to the naked eye has a magnitude of 6, compare its brightness with that of planet Venus which has a magnitude of - 4.
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Q. 28. Derive an expression for the energy stored in a parallel plate capacitor with air as the medium between its plates. How does the total energy stored by the capacitor change when the medium of air is replaced by a medium of dielectric constant k? Explain.
Answer
Q. 29. By using Bohr’s postulates of atomic model derive mathemati¬cal expressions for (i) kinetic energy and (ii) potential energy, of an electron revolving in an orbit of radius r. How does the potential energy change with increase in the principal quantum number (n) for the electron and why?
Answer
Q. 30. (a) Draw the graphs showing the variation of reactance of (i) a capacitor, and (ii) an inductor with the frequency of an a.c circuit.
(b) 11 KW of electric power can be transmitted to a distant station at (0 220 V, or (ii) 22,000 V. Which of the two modes of transmission should be preferred and why? Support your answer with possible calculations.
Or
Prove that an ideal inductor does not dissipate power in an a.c. circuit, A sinusoidal voltage V = 200 sin 3141 is applied to a resistor of 10 Ω resistance. Calculate
(i) rms value of the voltage, (ii) rms value of the current, and (iii) power dissipated as heat in watts.
Answer
Q. 1. Horizontal component of Earth’s magnetic field at a place is √3 times the vertical component. What is the value of angle of dip at this place?
Answer
Q. 2. Force between two point electric charges kept at a distance d apart in air is F. If these charges are kept at the same distance in water, how does the force between them change?
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Q. 3. Give any two factors on which thermo-electric emf produced in a thermo-couple depends.
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Q. 4. The electric current in a wire in the direction from B to A is decreasing. What is the direction of induced current in the metallic loop kept above the wire as shown in the figure?
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Q. 5. Name the electromagnetic radiations used for viewing objects through haze and fog.
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Q. 6. Give the ratio of the number of holes and the number of conduction electrons in an intrinsic semiconductor.
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Q. 7. In the given diagram, is the diode D forward or reversed biased?
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Q. 8. Name the planet which has maximum value of albedo.
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Q. 9. Two point electric charges of unknown magnitude and sign are placed a distance‘d’ apart. The electric field intensity is zero at a point, not between the charges but on the line joining them. Write two essential conditions for this to happen,
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Q. 10. The variation of potential difference V with length I in case of two potentiometers X and y is as shown in the given diagram. Which one of these two will you prefer for comparing emf’s of two cells and why?
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Q. 11. Name any one material having a small value of temperature coefficient of resistance. Write one use of this material,
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Q. 12. Write two advantages and two disadvantages of a secondary cell over a primary cell.
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Q. 13. In the figure, the straight wire AB is stationary and the coil abed can move. In which direction abed moves? Why?
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Q. 14. A radio frequency choke is air-cored coil whereas an audio frequency choke is iron-cored. Give reasons for this difference.
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Q. 15. An astronomical telescope consists of two thin lenses set 36 cm apart and has a magnifying power 8. Calculate the focal lengths of the lenses.
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Q. 16. Use the mirror formula to show that for an object lying between the pole and focus of a concave mirror, the image formed is always virtual in nature.
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Q. 17. An a-particle and a proton ace accelerated through the same potential difference. Calculate the ratio of velocities acquired by two particles.
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Q. 18. Describe the method used for determination of distance of a planet by parallax method.
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Q. 19. Explain the principle of a tangent galvanometer. How does the reduction factor of the galvanometer change, when (/) number of turns of the coil is increased and (it) radius of the coil is decreased? Give reason for your answer in each case.
Answer
Q. 20. A wire of uniform cross-section and length I has a resistance of 16 Ω. It is cut into four equal parts. Each part is stretched uniformly to length / and all the four stretched parts are connected in parallel. Calculate the total resistance of the combination so formed. Assume that stretching of wire does not cause any change in the density of its material.
Answer
Q. 21. An electric heater and an electric bulb are rated 500 W—220 V and 100 W—220 V respectively. Both are connected in series to a 220 V a.c. mains. Calculate the power consumed by (0 the heater and (n) electric bulb.
Answer
Q. 22. Why is diffraction of sound waves easier to observe than diffraction of light waves? What two main changes in diffraction pattern of a single slit will you observe when the monochromatic source of light is replaced by a source of white light?
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Q. 23. Explain surface wave and sky wave propagations of radio waves. Why is short wave communication over long distances not possible by surface wave propagation?
Answer
Q. 24. Give reasons for following observations on the surface of moon:
(i) Sun-rise and sun-set are abrupt
(ii) Sky appears dark
(iii) A rainbow is never observed.
Answer
Q. 25. The energy levels of an atom of element are shown in the following diagram. Which one of the level transitions will result in the emission of photons of wavelength 620 nm? Support your answer with mathematical calculations.
Answer
Q. 26. Give the logic symbol and truth table for AND gate. Explain, with the help of a circuit diagram, how this gate is realised in practice.
Answer
Q. 27. Drawing a labelled circuit diagram, explain how a NPN tran¬sistor can be used as an amplifier in common base configuration.
Answer
Q. 28. Explain the effect of introducing a dielectric slab between the plates of a parallel plate capacitor on its capacitance. Derive an expression for its capacitance with dielectric as the medium between the plates.
Or
Give the principle and explain the working of a van de Graaff generator with the help of a labelled diagram.
Answer
Q. 29. Distinguish between reactance and impedance. When a series combination of a coil of inductance L and a resistor of resistance R is connected across a 12 V, 50 Hz supply, a current of 0.5A flows through the circuit. The current differs in phase from applied voltage by π/3 radian. Calculate the value of L and R.
Answer
Q. 30. Explain the process of release of energy in a nuclear reactor. Draw a labelled diagram of a nuclear reactor and write the function of each part.
Answer
Q. 1. Sketch the electric lines of force for two positive charges Q1 and Q2 (Q1 > Q2) separated by a distance d.
Answer
Q. 2. Why is a voltmeter always connected in parallel with a circuit element across which voltage is to be measured?
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Q. 3. What is ‘ ‘Seebeck coefficient’?
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Q. 4. Mention two properties of the alloy from which permanent magnets are made.
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Q. 5. Give the direction in which the induced current flows in the wire loop, when the magnet moves towards it as shown in the figure.
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Q. 6. Why do long distance radio broadcast use short wave bands?
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Q. 7. At what angle of incidence should a light beam strike a glass slab of refractive index V3, such that the reflected and the refracted rays perpendicular to each other?
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Q. 8. Name a planet which shows phases like the moon.
Answer
Q. 9. Two point charges + 4 μC and - 6 μC are separated by a distance of 20 cm in air. At what point on the line joining the two charges is the electric potential zero?
Answer
Q. 10. State Faraday’s first law of electrolysis. How is it used?
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Q. 11. An electron of kinetic energy 25 keV moves perpendicular to the direction of a uniform magnetic Held of 0.2 millitesla. Calculate the time period of rotation of the electron in the magnetic field.
Answer
Q. 12. Define the coefficient of self-inductance. Write its unit. Give two factors on which the self-inductance of a long solenoid depends.
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Q. 13. Briefly describe the work of Maxwell and Hertz in the field of electromagnetic waves.
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Q. 14. A glass prism of refracting angle 60° and refractive index 1.5 is completely immersed in water of refractive index 1.33. Calculate the angle of minimum deviation of the prism in this situation. (sin-1 0.56 = 34.3°)
Answer
Q. 15. Draw a labelled ray diagram showing the formation of image of a distant object in an astronomical telescope.
Answer
Q. 16. Obtain the expression for the maximum kinetic energy of the electrons emitted from a metal surface in terms of the frequency of the incident radiation and the threshold frequency.
Answer
Q. 17. Pure silicon at 300 K has equal electron and hole concentra¬tions of 1.5 x 1016/m3. Doping by indium increases the hole concentration to 4.5 x 1022/m3. Calculate the new electron concentration in the doped silicon.
Answer
Q. 18. With the help of a diagram, describe the method of determining the diameter of a planet.
Answer
Q. 19. ‘n’ identical cells each of emf ‘E’ and internal resistance ‘r’ are connected in series to a resistor ‘R’.
(i) Deduce an expression for the internal resistance ‘r’ of one cell in terms of the current ‘I’ flowing through the circuit.
(ii) How does the internal resistance of the cell vary with temperature?
Answer
Q. 20. Calculate the current drawn from the battery in the given network sketched here.
Answer
Q. 21. Derive the expression for the force between two infinitely long parallel straight wires carrying current in the same direction. Hence define one ampere.
Answer
Q. 22. A magnet oscillating in a horizontal plane, has a time period of 3 seconds at a place where the angle of dip is 30° and 4 seconds at another place, where the dip is 60°. Compare the resultant magnetic field at the two places.
Answer
Q. 23. Verify Snell’s law of refraction using Huygen’s wave theory.
Answer
Q. 24. A double convex lens made of glass of refractive index 1.5 has both radii of curvature of magnitude 20 cm. An object 2 cm high is placed at 10 cm from the lens. Find the position, nature and size of the image.
Answer
Q. 25. State two properties of nuclear forces. Prove that the density of matter in nuclei is independent of mass number A.
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Q. 26. The output of a 2-input AND gate is fed to a NOT gate. Draw the logic circuit of the combination of gates. Give its logic symbol and write down its truth table.
Answer
Q. 27. Draw a circuit diagram of a common-emitter amplifier using a n-p-n transistor. Prove that in this amplifier, the output voltage is 180° out of phase with the input voltage.
Answer
Q. 28. An electric dipole is held in a uniform electric field. (i) Show that no translatory force acts on it. (ii) Derive an expression for the torque acting on it.
(iii) The dipole is aligned parallel to the field. Calculate the work done in rotating it through 180°.
Or
(i) Derive an expression for the energy stored in a parallel plate capacitor with air as the medium between its plates.
(ii) Air is replaced by a dielectric medium of dielectric constant ‘k’. How does it change the total energy of the capacitor?
Answer
Q. 29. (a) Draw the variation of the following with the frequency of the a.c. source
((i) reactance of an inductor, and
(ii) reactance of a capacitor.
(b) An a.c. circuit having an inductor and a resistor in series draws a power of 560 W from an a.c. source marked 210 V, 60 Hz. If the power factor of the circuit is 0.8, calculate ‘
(i) the impedance of the circuit, and
(ii) the inductance of the inductor used.
Answer
Q. 30. Draw a labelled diagram of Thomson’s set-up to find e/m of electrons. Briefly explain how the velocity of the electrons is determined? Assume that the p.d. between the cathode and the anode is the same as that between the two deflecting plates. If this p.d. is doubled, calculate by what factor the magnetic field should be changed to keep the electron beam still undeflected.
Answer
1. How does the luminosity of a star vary with its mass?
Answer
2. State two factors by which the range of transmission of signals by a T.V. tower can be increased.
Answer
3. The ratio of the horizontal component to the resultant magnetic field of earth at a given place is 1/√2. What is the angle of dip at that place?
Answer
4. Why is a dark region observed in a discharge tube at very low pressures?
Answer
5. What is the ratio of the nuclear densities of two nuclei having mass numbers in the ratio 1: 4?
Answer
6. If the frequency of the a.c. source in a LCR series circuit is increased, how does the current in the circuit change?
Answer
7. What is the work done in moving a 2 microcoulomb point charge from corner A to corner B of a Square ABCD when a 10 µC charge exists at the center of the square?
Answer
8. Why is the terminal voltage across a battery more than its e.m.f. during re-charging?
Answer
9. An electric flux of -5 x 103 Nm2 C -1 passes through a spherical Gaussian surface of radius 20 cm due to the charge placed at its center.
(i) Calculate the charge enclosed by the Gaussian surface.
(ii) If the radius of the Gaussian surface is double, how much flux would pass through the surface?
Answer
10. The variation of resistance of a metallic conductor with temperature is given below:-
(i) Calculate the temperature coefficient of resistance from the graph.
(ii) State why the resistance of the conductor increase with rise in temperature.
Answer
11. Three identical ceils, each of e.m.f. 2 V, are connected in parallel. This combination is connected to a 5 ohm resistor. If the terminal voltage across the cells in the closed circuit is 1.5 V, calculate the internal resistance of each cell.
Answer
12. Using Stefan’s Law, explain briefly how the surface temperature of a planet can be measured.
Answer
13. Define resolving power of a telescope. How does diffraction limit its resolving power?
Answer
14. Define the terms (i) luminous intensity and («) illuminance. Write the relation between them.
Answer
15. An irregular shaped wire PQRS (as shown in figure) placed in a uniform magnetic field perpendicular to the plane of the paper changes into a circular shape. State, with reason, the direction of the induced current in the loop
Answer
16. Using a logic circuit, explain briefly how a 2-input NAND gate can be converted into a NOT gate.
Answer
17. The thermo-emf of a thermo-couple is given by
E = αθ +1/2 βθ2
θ is the temperature of the hot junction ; α and β are the constants of the thermo-couple.
(0 Deduce an expression for the neutral temperature.
(ii) State two factors on which the temperature of inversion of a thermo-couple depends.
Answer
18. The current sensitivity of a moving coil galvanometer increases by 20% when its resistance is increased by a factor of two. Calculate by what factor the voltage sensitivity changes.
Answer
19. Calculate the equivalent resistance between the points A and B of the electric network given below.
Answer
20. An electron beam of velocity v, moving in the plane of paper enters a region of uniform magnetic field which is perpendicular to the plane of the paper, and travels in a circular path.
(i) Deduce an expression for the time-period of the electron. (ii) Does the kinetic energy of electron change during this time? Give reason.
Answer
21. State two conditions for obtaining sustained interference pattern. What is the effect on the interference pattern in Young’s double-slit experiment due to each of the following operations?
(a) The widths of the two slits are increased equally.
(b) The whole apparatus is kept in a denser medium.
Answer
22. Sketch a graph showing the dependence of intensity of transmitted light on the angle of rotation between a polarizer and an analyser. Aray of light is incident at an angle of incidence ip on the surface of separation between air and a medium of refractive index μ, such that the angle between the reflected and refracted rays is 90°. Obtain the relation between ip and μ.
Answer
23. Draw a labelled ray diagram to show the formation of image of an object in a compound microscope. Write the expression for its magnifying power.
Answer
24. CO Why is the energy variation of the electrons emitted during a beta decay continuous?
(ii) Explain, with an example, whether the neutron-proton ratio increases or decreases during beta decay.
Answer
25. What is a zener diode? Give its symbolic representation. With the help of a circuit diagram, explain how it can be used as a voltage stabilizer.
Answer
26. (i) Draw a circuit diagram of a p-n-p transistor as an amplifier in a common emitter configuration.
(ii) Calculate the voltage gain for a transistor having a current gain 40, collector resistance 6 kilo-ohm and input resistance 1 kilo-ohm.
Answer
27. State the underlying principle of a tangent galvanometer. Write briefly how it can be used to determine the horizontal component of earth’s magnetic field at a given place.
Answer
28. Derive the expression for the energy stored in a charged capacitor. Show that there is always a loss of energy on connecting the two charged capacitors having capacitance C1, C2 and potentials V1 V2.
Or
Explain the construction and working of a Van de Graff generator with the help of a labelled diagram. Mention its use.
Answer
29. (i) Write the working principle of a starter used along with a choke in a fluorescent tube.
(ii) An inductance coil has a resistance of 100 ohm. When a.c. signal of frequency 1000 Hz is applied to the coil, the applied voltage leads the current by 45°. Calculate the self-inductance of the coil.
Answer
30. Draw a labelled diagram of Millikan’s oil drop experiment to determine the charge of an electron. Give its working principle.
Derive the expression for the charge in terms of the various parameters involved in the experiment. Mention the other fundamental information, besides the determination of the charge, drawn from this experiment.
Answer
Q. 1. Name the physical quantity whose SI unit is Coulomb/Volt.
Answer
Q. 2. Write the frequency limit of visible range of electromagnetic spectrum in kHz.
Answer
Q. 3. How does the conductance of a semi-conducting material change with rise in temperature?
Answer
Q. 4. The force F experienced by a particle of charge e moving with velocity v in a magnetic field B is given by Of these, name the pairs of vectors which are always at right angles to each other.
Answer
Q. 5. Two wires A and B are of same metal, have the same area of cross-section and have their lengths in the ratio 2:1. What will be the ratio of currents flowing through them respectively when the same potential difference is applied across length of each of them?
Answer
Q. 6. Calculate the rms value of the alternating current shown in the figure.
Answer
Q. 7. The image of an object formed by a lens on the screen is not in sharp focus. Suggest a method to get clear focusing of the image on the screen without disturbing the position of the object, the lens or the screen.
Answer
Q. 8. Two protons A and B are placed between two parallel plates having a potential difference V as shown in the figure. Will these protons experience equal or unequal force?
Answer
Q. 9. Define the terms ‘threshold frequency’ and ’stopping potential’ for photo-electric effect. Show graphically how the stopping potential, for a given metal, varies with frequency of the incident radiations. Mark threshold frequency on this graph.
Answer
Q. 10. Draw labelled diagram of a Leclanche cell. Write the function of charcoal powder and manganese dioxide used in its porous pot.
Answer
Q. 11. How does the mutual inductance of a pair of coils change when:
(i) the distance between the coils is increased ?
(ii) the number of turns in each coil is decreased ?
Justify your answer in each case.
Answer
Q. 12. Define the terms magnetic inclination and horizontal com¬ponent of Earth’s magnetic field at a place. Establish the relationship between the two with the help of a diagram.
Answer
Q. 13. An electron in an atom revolves around the nucleus in an orbit of radius 0.53 A. Calculate the equivalent magnetic moment if the frequen¬cy of revolution of electron is 6.8 x 109 MHz.
Answer
Q. 14. Write the function of base region of a transistor. Why is this region made thin and slightly doped?
Answer
Q. 15. Derive an expression for the energy stored in a charged parallel plate capacitor with air as the medium between its plates.
Answer
Q. 16. In the diagram given below for the stationary orbits of the hydrogen atom, mark the transitions representing the Balmer and Lyman series.
Answer
Q. 17. The given figure shows an inductor L and resistor R connected in parallel to a battery B through a switch S. The resistance of R is the same as that of the coil that makes L. Two identical bulbs, P and Q are put in each arm of the circuit as shown.
When S is closed, which of the two bulbs will light up earlier? Justify your answer.
Answer
Q. 18. Two point electric charges of values q and Iq are kept at a distance d apart from each other in air. A third charge Q is to be kept along the same line in such a way that the net force acting on q and 2q is zero. Calculate the position of charge Q in terms of q and d.
Answer
Q. 19. Explain, with the help of a circuit diagram, the use of potentiometer for determination of internal resistance of a primary cell. Derive the necessary mathematical expression.
Answer
Q. 20. (i) Sketch the wave-fronts corresponding to converging rays. (ii) Verify Snell’s law of refraction using Huygens’ wave theory.
Answer
Q. 21. An electric dipole is held in a uniform electric field. (i) Show that no translator}’ force acts on it
(ii) Derive an expression for the torque acting on it
Answer
Q. 22. Derive an expression for the width of the central maxima for diffraction of light at a single slit. How does this width change with increase in width of the slit?
Answer
Q. 23. A capacitor of capacitance 100 μF and a coil of resistance 50Ω and inductance 0.5 H are connected in series with a 110V, 50 Hz source. Calculate the rms value of the current in the circuit.
Answer
Q. 24. Draw a labelled ray diagram to show the image formation in a reflecting type telescope. Write its two advantages over a refracting type telescope. On what factors does its resolving power depend?
Answer
Q. 25. Define the terms ’solar constant’ and ’solar luminosity’. Explain how their knowledge helps us to calculate the surface temperature of the sun. Derive the necessary mathematical expression.
Answer
Q. 26. An object is kept in front of a concave mirror of focal length 15 cm. The image formed is three times the size of the object. Calculate two possible distances of the object from the mirror.
Answer
Q. 27. A voltmeter V of resistance 400 Ω is used to measure the potential difference across a 100 Ω. resistor in the circuit shown here.
(a) What will be the reading on the voltmeter?
(b) Calculate the potential difference across 100 Ω resistor before the voltmeter is connected.
Answer
Q. 28. Derive a mathematical expression for the force per unit length acting on each of the two straight parallel metallic conductors carrying current in the same direction and kept near each other. Why do such current carrying conductors attract each other?
Or
Derive a mathematical expression for the force acting on a current carrying straight conductor kept in a magnetic field. State the rule used to determine the direction of this force.
Answer
Q. 29. (i) Draw a labelled diagram of Thomson’s experimental set-up to determine e/m of electrons, (ii) Explain, by deriving the necessary mathematical expression, how e/m of electrons can be determined by this method.
Answer
Q. 30. Define the terms ‘potential barrier’ and ‘depiction region’ for a p-n junction. Explain, with the help of a circuit diagram, the use of a p-n diode as a full wave rectifier. Draw the input and output wave-forms.
Answer
Q. 1. Name the physical quantity whose SI unit is Coulomb/Volt.
Answer
Q. 2. Write the frequency limit of visible range of electromagnetic spectrum in kHz.
Answer
Q. 3. How does the conductance of a semi-conducting material change with rise in temperature?
Answer
Q. 4. The force F experienced by a particle of charge e moving with velocity v in a magnetic field B is given by Of these, name the pairs of vectors which are always at right angles to each other.
Answer
Q. 5. Two wires A and B are of same metal, have the same area of cross-section and have their lengths in the ratio 2:1. What will be the ratio of currents flowing through them respectively when the same potential difference is applied across length of each of them?
Answer
Q. 6. Calculate the rms value of the alternating current shown in the figure.
Answer
Q. 7. The image of an object formed by a lens on the screen is not in sharp focus. Suggest a method to get clear focusing of the image on the screen without disturbing the position of the object, the lens or the screen.
Answer
Q. 8. Two protons A and B are placed between two parallel plates having a potential difference V as shown in the figure. Will these protons experience equal or unequal force?
Answer
Q. 9. Define the terms ‘threshold frequency’ and ’stopping potential’ for photo-electric effect. Show graphically how the stopping potential, for a given metal, varies with frequency of the incident radiations. Mark threshold frequency on this graph.
Answer
Q. 10. Draw labelled diagram of a Leclanche cell. Write the function of charcoal powder and manganese dioxide used in its porous pot.
Answer
Q. 11. How does the mutual inductance of a pair of coils change when:
(i) the distance between the coils is increased ?
(ii) the number of turns in each coil is decreased ?
Justify your answer in each case.
Answer
Q. 12. Define the terms magnetic inclination and horizontal com¬ponent of Earth’s magnetic field at a place. Establish the relationship between the two with the help of a diagram.
Answer
Q. 13. An electron in an atom revolves around the nucleus in an orbit of radius 0.53 A. Calculate the equivalent magnetic moment if the frequen¬cy of revolution of electron is 6.8 x 109 MHz.
Answer
Q. 14. Write the function of base region of a transistor. Why is this region made thin and slightly doped?
Answer
Q. 15. Derive an expression for the energy stored in a charged parallel plate capacitor with air as the medium between its plates.
Answer
Q. 16. In the diagram given below for the stationary orbits of the hydrogen atom, mark the transitions representing the Balmer and Lyman series.
Answer
Q. 17. The given figure shows an inductor L and resistor R connected in parallel to a battery B through a switch S. The resistance of R is the same as that of the coil that makes L. Two identical bulbs, P and Q are put in each arm of the circuit as shown.
When S is closed, which of the two bulbs will light up earlier? Justify your answer.
Answer
Q. 18. Two point electric charges of values q and Iq are kept at a distance d apart from each other in air. A third charge Q is to be kept along the same line in such a way that the net force acting on q and 2q is zero. Calculate the position of charge Q in terms of q and d.
Answer
Q. 19. Explain, with the help of a circuit diagram, the use of potentiometer for determination of internal resistance of a primary cell. Derive the necessary mathematical expression.
Answer
Q. 20. (i) Sketch the wave-fronts corresponding to converging rays. (ii) Verify Snell’s law of refraction using Huygens’ wave theory.
Answer
Q. 21. An electric dipole is held in a uniform electric field. (i) Show that no translator}’ force acts on it
(ii) Derive an expression for the torque acting on it
Answer
Q. 22. Derive an expression for the width of the central maxima for diffraction of light at a single slit. How does this width change with increase in width of the slit?
Answer
Q. 23. A capacitor of capacitance 100 μF and a coil of resistance 50Ω and inductance 0.5 H are connected in series with a 110V, 50 Hz source. Calculate the rms value of the current in the circuit.
Answer
Q. 24. Draw a labelled ray diagram to show the image formation in a reflecting type telescope. Write its two advantages over a refracting type telescope. On what factors does its resolving power depend?
Answer
Q. 25. Define the terms ’solar constant’ and ’solar luminosity’. Explain how their knowledge helps us to calculate the surface temperature of the sun. Derive the necessary mathematical expression.
Answer
Q. 26. An object is kept in front of a concave mirror of focal length 15 cm. The image formed is three times the size of the object. Calculate two possible distances of the object from the mirror.
Answer
Q. 27. A voltmeter V of resistance 400 Ω is used to measure the potential difference across a 100 Ω. resistor in the circuit shown here.
(a) What will be the reading on the voltmeter?
(b) Calculate the potential difference across 100 Ω resistor before the voltmeter is connected.
Answer
Q. 28. Derive a mathematical expression for the force per unit length acting on each of the two straight parallel metallic conductors carrying current in the same direction and kept near each other. Why do such current carrying conductors attract each other?
Or
Derive a mathematical expression for the force acting on a current carrying straight conductor kept in a magnetic field. State the rule used to determine the direction of this force.
Answer
Q. 29. (i) Draw a labelled diagram of Thomson’s experimental set-up to determine e/m of electrons, (ii) Explain, by deriving the necessary mathematical expression, how e/m of electrons can be determined by this method.
Answer
Q. 30. Define the terms ‘potential barrier’ and ‘depiction region’ for a p-n junction. Explain, with the help of a circuit diagram, the use of a p-n diode as a full wave rectifier. Draw the input and output wave-forms.
Answer
Q. 1. An electron and a proton are free to move in a given electric field. Will the acceleration experienced by them be equal or different?
Answer
Q. 2. Is the potential difference across the two p.n. junctions in the given circuit same or different?
Answer
Q. 3. The current-voltage graphs for a given metallic conductor at two different temperatures T1 and T2 are as shown in the diagram. Which of these two temperatures is higher?
Answer
Q. 4. A charged particle enters a uniform magnetic field at right angles. Of these three
(i) its kinetic energy,
(ii) its speed and
(iii) its linear momentum, which will change on entering the field region ?
Answer
Q. 5. Write the truth table for the NOT gate.
Answer
Q. 6. Give an example of interference of light from daily life situations.
Answer
Q. 7. Two thin lenses, of powers, 10D and - 5D are put together. What is the focal length of the combination?
Answer
Q. 8. Work functions for two metals A and B are 2 eV and 5 eV respectively. Which one of the two has higher threshold wavelength?
Answer
Q. 9. A charge q is placed at the centre of the line joining two equal charges Q and Q. Calculate the value of charge q such that all the three charges are in equilibrium. Also mention the nature of this charge.
Answer
Q. 10. State Faraday’s laws of electrolysis.
Answer
Q. 11. Of the two identical galvanometers, one is to be converted into an ammeter and the other into a milliammeter. Which of the two shunts will be of larger resistance and why?
Answer
Q. 12. Define ‘angle of dip’. What is the value of angle of dip at a place where horizontal and vertical components of earth’s magnetic field are equal?
Answer
Q. 13. Explain how a current carrying metallic loop acts as a magnetic dipole. How is the magnetic dipole moment affected on increasing the value of the current flowing through the loop?
Answer
Q. 14. Define ‘angular dispersion’ and ‘dispersive power’ for a prism. Write two factors on which the angular dispersion produced by a prism depends.
Answer
Q. 15. Calculate the distance at which an object should be placed in front of a thin convex lens of focal length 10 cm to obtain a virtual image of double its size.
Answer
Q. 16. You are given three lenses having powers P and apertures A as under:
P1 = 5D ; A1 = 2 cm
P2 = 2D ; A2 = 10 cm
P3 = 10D ; A3 = 1 cm
Which of the two lenses will you select to construct a telescope and why?
Answer
Q. 17. Binding energy per nucleon for deutron (1H2) and helium (2He4) are 1.1 MeV and 7.0 MeV respectively. Calculate the energy released when two deutrons fuse together to form a helium nucleus.
Answer
Q. 18. Using Bohr’s postulate, derive an expression for the radius of the nth orbit of the electron in hydrogen atom.
Answer
Q. 19. For measuring e.m.f’s of cells, a potentiometer is preferred over a voltmeter. Why? The length of a potentiometer wire is 5 metres. It is connected to a battery of constant emf. For a given Leclanche cell, the position of zero galvanometer deflection is obtained at 100 cm. If the length of potentiometer wire be made S metres instead of 5 metres, calculate the length of wire for zero deflection in galvanometer for the same Leclanche cell.
Answer
Q. 20. By applying Kirchh off s laws, calculate the current flowing through each resistance in the network shown in this diagram.
Answer
Q. 21. Explain why two straight parallel metallic wires carrying electric current in the same direction, attract each other. Derive an expres¬sion for the force experienced in this situation.
Answer
Q. 22. An air core coil and an electric bulb are connected in series across a 220 V, 50 Hz a.c. source. The bulb glows with some brightness. How will the glow of the bulb be affected when
(i) an iron rod is introduced into the coil and .
(ii) a capacitor is introduced in series in the circuit ? Justify your answer in each case.
Answer
Q. 23. Distinguish between ground wave propagation and sky wave propagation of radio waves. Why can sky wave propagation be not used for long distance T.V. transmission?
Answer
Q. 24. Describe an experiment to demonstrate transverse wave nature of light.
Answer
Q. 25. A transistor is used in common-emitter mode in an amplifier circuit. When a signal of 20 mV is added to the base-emitter voltage, the base current changes by 20 μ A and the collector current changes by 2mA. The load resistance is 5 x 103 Ω. Calculate (0 current gain, and (ii) voltage gain of the transistor.
Answer
Q. 26. Define ’solar constant’ and ’solar luminosity’. Explain how their knowledge helps us to determine the surface temperature of the Derive the formula used.
Answer
Q. 27. Distinguish between a conductor, an insulator and a semicon¬ductor on the basis of energy-band diagram.
Answer
Q. 28. With the help of a labelled diagram, explain the principle, construction and working of a transformer. Why is the core of a transformer laminated?
Or
With the help of a labelled diagram, explain the principle, construction and working of an a.c. generator.
Answer
Q. 29. Define capacitance of a capacitor. Give its unit Derive an expression for the total capacitance when three capacitors of capacitances C1 C2 and C3 are connected in series. Write any two uses of capacitors in electrical circuits.
Answer
Q. 30. With the help of a labelled diagram, explain the principle and the method of determination of e/m of an electron by Thomson’s method. Derive the necessary formula.
Answer
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