CBSE Physics Model Practice Question Paper- 9
1. A magnetic needle lying parallel to a magnetic field requires W units of work to turn it through 60°. What is the torque needed to maintain the needle in this position?
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2. Give an example of wattless current.
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3. Why an electric iron with a thermostat used only with alternating current?
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4. What is self inductance of a coil in which current changes from 8 A to 2A in 3 x 10-2 sec induces an e.m.f. of 2V.
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5. Amongst α, β and γ which one has the least: (i) penetrating power (ii) ionization power?
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6. The voltmeter reads 120 V, what is its resistance?
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7. Germanium crystal is to be made n type. What must be done?
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8. In what ratio will the intensity of the image increase when the diameter of the objective of an astronomical telescope is doubled? How will the resolving power change?
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9. Write an expression for energy density of a magnetic field assuming that there is no magnetic material inside the field. Compare this expression with the energy density of an electrastatic field.
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10. In a single slit diffraction, the slit width is 0.050 cm and the wavelength is 632.8 nm. How far from the centre maximum is the third order maximum on a screen 10 m away?
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11. Draw impedance diagram of an LRC circuit. Construct a similar diagram for a circuit in which the current frequency is doubled and the maximum emf is the same and find how the current will change as a result of this.
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12. Find the value of Rydeberg constant in Bohr’s Theory for hydrogen atom. Write its units.
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13. What is astronomical units? How can it be computed?
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14. How can deviation without dispersion be obtained with the use of two lenses, one of crown glass and the other of flint glass?
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15. How can eddy currents be minimised?
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16. The magnetic forces are very much smaller than the electric forces. Verify this statement.
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17. Draw a diagram to illustrate Young’s double slit experiment. The distance between the slits is d. Determine the maximal number of fringes that can be observed for a light of wavelength λ.
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18. The objective of telescope A has a diameter 3 times that of the objective of telescope B. (i) How much greater amount of light is gathered by A compared to B?
(ii) What is the ratio of ranges A and B?
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19. Two polaroids are placed at 90° to each other and the transmitted intensity is zero. What happens when one morepolaroid is placed between these two bisecting the angle between them?
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20. (a) If magnetic monopoles existed, how would Gauss law for magnetism be modified ?
(b) The earth’s core contains iron. Does this mean that earth’s magnetism is due to iron?
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21. Determine the speed of electron in the n = 3 orbit of Li++.
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22. Calculate the first four energy states of a particle of mass m, moving freely along a length L and show these on a energy level diagram.
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23. Show that the kinetic energy of a charged particle does not change in a magnetic field.
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24. Why only coherent waves show interference?
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25. What is interference ? State the conditions of interference of light.
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26. What is depletion layer in ap-n-junction? Explain how is this layer formed.
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27. How can we obtain the mass of the milky way ?
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28. Show that the magnetic moment of a current loop is given by m = IA where / is the current in the loop and A its area.
How are small magnetic fields measured? Give the principle, theory and working of the apparatus used.
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29. A circuit consists of L and C in series joined to an a.c. Find the impedance.
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30. A metallic rod is moved with a uniform velocity over a rectangular frame placed in a magnetic field. Show that an e.m.f. is induced in it and find an expression for the work done.
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