CBSE Physics Sample Question Paper : Set-3
Q 1, Is electric flux a scalar or vector quantity? Write its SI unit.
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Q. 2. Name the wave phenomenon which is exhibited by light waves but not by the sound waves.
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Q. 3. Two star A and B have magnitudes of - 2 and 3 respectively, which of the two is brighter and by how much?
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Q. 4. Will the drift speed of free electrons in a metallic conductor increase or decrease with the increase in its temperature?
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Q. 5. A magnetic needle, free to rotate in a vertical plane, orients itself with its axis vertical at a certain place on the earth. What are the values of?
(a) horizontal component of earth’s magnetic field.
(b) angle of dip at this place.
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Q. 7. A steady current flows in a metallic conductor of non-uniform cross-section. Which of the following quantities is are constant along the conductor: current, current density, drift speed,
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Q. 8. The variation of p, d. with length in case of two potentiometers A and B as given below, which of the two is more sensitive?
Q. 9. State Kirchhoffs laws for an electric network.
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Q. 10. What is meant by ‘interference of light’? Write any two conditions necessary for obtaining well-defined and sustained interference pattern of light.
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Q. 11. Define the angular dispersion. Draw the path of a ray of white light passing through a prism and mark angular dispersion on it.
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Q. 12. The radius of curvature of each surface of a convex lens of refractive index 1.5 is 40 cm. Calculate its power.
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Q. 13. Obtain the relation between the frequency of revolution of a planet and its orbital radius.
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Q. 14. A sphere Si, of radius rt encloses a total charge Q. If there is another concentric sphere S2 of radius r2 (r2 >r1) and there is no additional charges between S1 and S2, find the ratio of electric flux through Si and S2.
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Q. 15. A simple voltaic cell has an e.m.f. of 10 V. Is there a net field inside the cell when (i) circuit is open (ii) circuit is closed and a steady current is drawn from it. Explain your answers in each case.
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Q. 16. Suppose a helical spring is suspended from the roof of a room and a very small weight attached to its lower end. What will happen to the spring when a current is passed through it. Give reasons to support your answer.
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Q. 17. A charged oil drop falls under gravity with a terminal speed v. The drop is held stationary by applying suitable electric field in a Millikans set up and is found to carry 2 excess electron. Suddenly the drop is observed to move upwards with the same velocity. Why does the drop move upward. Write relevant mathematical equations in support of your answer.
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Q. 18. If the emitter and the base of a npn transistor have the same doping concentration. Explain how will the collector and base currents be affected?
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Q. 19. What is See beck effect? Draw a curve to show the variation of thermo e.m.f. with the gradual increase in the temperature of hot junction. Mark the neutral temperature and temperature of inversion of the thermocouple on the curve.
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Q. 20. Draw the logic symbol and write the truth table of AND gate. With the help of a circuit diagram describe the realisation of AND gate using semiconductor diodes.
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Q. 21. What is meant by the current sensitivity of a moving coil galvanometer? On what factors does it depend? In an exercise to increase current sensitivity of a galvanometer by 25% its resistance is also increased 1.5 times. How will the voltage sensitivity of the galvanometer be effected?
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Q. 22. An electron beam of initial energy 18 keV moving horizontally is subjected to a horizontal magnetic field of 0.4 G normal to the initial direction. Calculate the vertical deflection of the beam over a distance of 30 cm.
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Q. 23. When 100 V DC is applied across an inductor, a current of 1A flows through it. If the same inductor is connected to a 100 V AC source the current reduces to 0.5 A. Why is the current reduced in the later case? Calculate the value of reactance of the inductor.
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Q. 24. Monochromatic light of wavelength 589 nm is incident from air on water surface. What are the values of wavelength, frequency and speed of (a) reflected light (b) refracted light. Refractive index of water is 1.33.
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Q. 25. A radioactive isotope decays in the following sequence:
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If the mass number and atomic number of A2 are 176 and 71 respec¬tively, find the mass number and atomic number of Ai and A. Which of the three elements are isobars?
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Q. 26. With the help of a circuit diagram explain the use of npn transistor as an amplifier in common emitter configuration. What is the phase relation between collector and base voltage?
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Q. 27. Using the data given below, state which two of the given lenses will you prefer to construct a best possible (0 telescope (ii) microscope. Also indicate which of the selected lenses is to be used, as an objective and eye piece in each case.
Lenses Power (P) Aperture (A)
L1 6D lcm
L2 3D 8 cm
L3 10D 1 cm
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Q. 28. State Bohr’s postulate of atomic model. Derive an expression for the energy of an electron.
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Q. 29. A parallel plate capacitor with air between its plate having plate area of 6 x 10- 3 m2 and separation between them 3 mm is connected to a 100 V supply. Calculate charge on each plate of the capacitor. Explain what would happen when a 3 mm thick mica sheet (dielectric constant, K = 6) is inserted between the plates.
(i) While the voltage supply remains connected. :
(ii) After the supply is disconnected.
Derive an expression for the energy stored in a capacitor of capacitance C. When it is charged by connecting it to a battery of pd V. Now if the capacitor is disconnected from the battery. What will be the energy stored in the capacitor? When (i) separation between the plates is doubled and (ii) an uncharged identical capacitor is connected across it.
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Q. 30. A small town with a demand of 880 kW of electric power at 220 V is situated 15 km away from an electric plant generating power at 440 V.
The resistance of the cable carrying power is 15Ω. The town gets power through a 4400 - 220 V step down transformer at a sub-station in the town.
(i) Calculate the line power loss in the form of heat.
(ii) How much power must the plant supply, assuming there is a negligible power loss due to leakage?
(iii) Calculate the voltage drop in the line.
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