CBSE Physics Model Practice Question Paper- 8
1. Name the electromagnetic radiation produced from transition in outer energy levels of an atom.
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2. What is the effect of doping in a pure semiconductor?
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3. Draw graphs showing variation of output voltage with current in load for unregulated power supply and regulated power supply.
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4. A capacitor of capacitance 2µF is charged to 200 V. It is now discharged through a resistance of 2 Q, what is the heat produced in the resistance?
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5. An a.c. source is 120 V - 60 Hz. What is the voltage after 1/720 sec from the time the sine curve of a.c. starts?
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6. Name two superior and inferior planets?
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7. Define thermopo wer of a thermocouple.
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8. What is the magnetic moment of an atom of a diamagnetic?
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9. Draw an approximate graph showing change in resistivity of metals with the rise in temperature from OK to sufficiently above the room temperature. Why there is resistivity even at 0 K?
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10. (i) Write the formula for the power of an alternating current. What is power factor?
(ii) What is a wattless current?
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11. Find the potential difference between the points a and b.
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12. A convex lens of focal length 20 cm and a concave lens of focal length 10 cm are arranged a distance apart. A parallel beam of light falls on the convex lens and leaves the concave lenses as aparallel beam. What is the distance between the lenses?
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13. In a hydrogen spectrum the frequency for transition ni =3 to nf = 2 is v and for transition 3i = 2 to nf = 1 is 121.5 nm is v’. What is the frequency for transitions ni = 3 to nf =l?
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14. Derive a relation between the apparent depth and real depth of objective in denser media.
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15. The voltage across the terminals of a battery of emf falls from 12 V to 10 V.
Find the silver plated at the cathode in 30minutes. Given internal resistance of the battery as 2Ω and atomic weight of silver 108 g/mole.
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16. Derive the mathematical expression for surface temperature of a planet in solar system.
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17. What is the potential difference Va - Vb in the circuit shown. Image
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18. Three point charges - 4q, q and - q are placed in a straight line of length l at point o, l/2 and I respectively. What is the net force on the charge _ q?
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19. The number of alpha particles emitted per minute by a small amount of a radioactive substance was 560 initially and 280 after 2 hours. What is the expected rate of emission after another four hours?
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20. Explain how the process of avalanche breakdown occurs in a pn junction diode? How is it different from Zener breakdown?
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21. Why a converging lens can never form a point image of a distant point source? If D is the distance from the lens at which the light is focussed. Write the expression for the radius of the first dark ring in the image. Describe the change in width of the central maximum of the single-slit diffraction pattern as the width of the slit is made smaller.
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22. A wire is bent into the shape shown in Fig. (a) and the magnetic field is measured at Pi, when the current is I. The same wire is bent into the shape of a chord shown in Fig. (b) and the magnetic field is measured at P2 with the same current /. If the total length of the wire is the same in each case, what is the ratio of B1 / B2?
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23. What are the limitations of the Huygen’s wave theory of light? A spherical wave of light falls on a concave lens. Draw a diagram to illustrate the refraction of the wave.
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24. What is magnetic flux? Give its dimensions. Differentiate between magnetising field H and magnetic field B. Write the expressions for their line integrals.
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25. Explain the principle of a potentiometer. Two potentiometers of equal resistance and length I, are connected in series and their sliding contacts are connected. In one potentiometer the sliding contact is kept fixed at the mid point How will the reading of me ammeter vary as the sliding contact of the second potentiometer is moved from one end to me other?
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26. Explain an approximate characteristic curve of a p-n junction diode.
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27. A lens forms a sharp image on a screen. A parallel sided transparent slab of refractive index (X is introduced between the lens and the screen. The image is disturbed and to refocus, it is found necessary to move the screen by a distance. In which direction the screen be moved? What is the thickness of the slab? Derive the expression.
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28. Explain the principle of an ac generator. When large current is drawn from an ac generator me frequency falls. Why?
How can a NOT gate be realised in practice? Draw a circuit diagram and explain with the help of truth table.
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29. Define work function of a metal. Explain how work function can be found from the experiment on photoelectric effect.
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30. A fluoroscent lamp taking 80 W at power factor 0.7 lagging from a 230 V, 50 Hz supply is to be corrected to power factor 1.0. Determine the value of the capacitor used.
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