CBSE Physics Model Question Paper- VIII
1. Galaxies are of many types. What type of galaxy is the milkyway?
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2. What is distance of nearest approach?
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3. Show that NC -1 and Vm-1 represent the same physical quantity.
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4. Which gas acts as shield for ultra-violet radiations?
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5. What is the quantity whose unit is seimen metre?
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6. What are fast breeder reactors?
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7. What is meant by extrinstic semiconductor?
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8. Eye is most sensative to green light but danger signals are red. Why so?
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9. Earth is quite warm. What.effect keeps it warm 7 Explain in 2-3 lines.
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10. What are SI units of R/L and CR?
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11. Show that in the region of strong electric fields, equipotential surfaces are close together.
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12. A circuit having an inducting reactance of 25 Ω, a capacitor of capacitive reactance of 31 Ω and resistor of reistance 8 Ω are all placed in series. What is the total impedance of the circuit?
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13. A voltmeter measuring 0-2 V has a resistance of 100 ohm. How can it be converted into an ammetre of range 0-5 A.?
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14. What are nuclear reactions? Name the conservation laws which must be obeyed for a nuclear reactions to start.
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15. What is Joule’s law? Deduce an expression for the heat produced in a wire when a current / flows through a resistor JR.
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16. Why capacitor blocks D.C., whereas inductor allows it an easy path. What offers larger resistance to A.C?
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17. What is (110 100 111)2 equal to?
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18. Why is the conductivity of an electrolyte very low as compared to a metal at room temperature?
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19. What are the laws of radioactive distintegratibn 7 how can the life of a rock be determined?
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20. Derive an expression for magnetic field at a point on the axis of a current loop.
How from this can we deduce magnetic field at the centre of the current carrying circular coil?
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21. A silver rod 1 m long and 1. 0 X 10-4 m2 area cross-section has one free electron per atom. Calculate (a) the number of free electrons in the rod, (b) the, drift velocity of the electrons if the current through the rod is 4A. Given the density of silver = 10.5 X 103 kg m-3 and mass number of silver = 108.
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22. Derive the expression for magnetic field acting at a point on the axis of a circular coil carrying current.
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23. Derive an expression for torque acting on a current carrying rectangular loop placed in the magnetic field.
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24. What is Q-factor of a series resonance circuit 7 what are uses of series resonant circuit?
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25. What are the properties of e.m. waves?
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26. A narrow monochromatic beam of light of intensity I is incident on a glass plate P as shown in figure. Another identical glass plate Q is held parallel and very close to P. Each glass plate reflects 25% of the light incident on it and-transmits the remaining. Find the ratio of min¬imum and maximum intensities in the inter¬ference pattern formed by the two beams obtained after one reflection at each plate.
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27. Derive the mirror formula for concave mirror forming virtual image.
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28. Compute the equivalent capacitance of the following combination be¬tween A and D if C1 = C2 = C3
= C4 = C5 = 8µF. If a battery of 10V is connected between these points, what will be the charge on eacli capacitor?
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What is Gauss theorem? Derive an expression for electric field intensity at a point inside two parallel sheats of charge and hence capacitance of a parallel plate capacitor with a conducting slab.
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29. What is Lenz maker’s formula? Derive an expression for Lenz maker’s formula for a convex lens.
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30. What is meant by rectification? How can we use diodes to get full wave A.C. rectified? How can the output be smoothened?
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