Download Class XII Physics 50 short questions

KV ONGC CHANDKHEDA
Question Bank 2015-16
Physics
Class XII
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Where the energy of capacitor does resides?
Do electrons tend to go to region of low or high potential?
What is the net charge on the charged capacitor?
A Gaussian surface encloses an electric dipole within it. What is the total flux across
sphere?
State Gauss’s law of electrostatics. Using it derive the expression for the electric filed
due to a) an uniformly charged conductor of infinite length. b)an infinitely large sheet
which is uniformly charged.c) an uniformly charged spherical shell.
Define electric dipole. Deduce the expression for the electric field at axial and
equatorial axis of the dipole.
Derive the relation between current and drift speed.D
Define the equipotential surface. State its important properties D
Draw the electric filed lines for a) a positive point charge.b) a negative point charge c)
an electric dipole .d) two like charges kept near each other.
10. State Kirchhoff’s voltage and current law.
11. . A ray of light while traveling from a denser to a rarer medium undergoes total
reflection.Derive the expression for the critical angle in terms of the speed of light in
the respective media.
12. Why is the focal length of an objective in compound microscope little shorter than the
focal length of the eyepiece?
13. How does the focal length of a convex lens change if monochromatic red light is used
instead of violet light?
14. What are the characteristics properties of electromagnetic waves?
15. What is the work done by a magnetic field on moving a charge? Give reason.
16. Why is copper wire not suitable for a potentiometer?
17. Explain the flow of charges in a metallic conductor.
18. Distinguish between drift velocity and mobility. Establish a relation between drift
velocity and current.
19. State Ohm’s law.
20. Define resistivity of a material. How are materials classified based on resistivity?
21. The colours of a carbon resistor is orange, orange, orange. What is the value of
resistor?
22. Draw a labelled ray diagram of a reflecting telescope. Mention its two advantages
over the refracting telescope.
23. Explain the effective resistance of a series network and parallel network.
24. A diverging lens of focal length F is cut into two identical parts, each forming a Plano
concave lens. What is the focal length of each part?
25. What is meant by ‘normal adjustment’ in case of an astronomical telescope? With
the help of a neat and labeled ray diagram, obtain an expression for the magnifying
power of the telescope in normal adjustment.
26. Deduce an expression for the force on a current carrying conductor placed in a
magnetic field.
27. Explain in detail the principle, construction and the theory of moving coil
galvanometer
28. Explain how you will convert a galvanometer into (i) an ammeter and (ii) a voltmeter.
29. Draw a circuit diagram of n-p-n transistor amplifier in CE configuration. Under what
condition does the transistor act as an amplifier?
30. In the circuit shown in the figure, identify the equivalent gate of the circuit and make
its truth table. 2
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33. How the size of depletion region changes when p-n junction diode is in
(a) forward bias (b) reverse bias and the conductivity of diode changes with bias.
34. What is zener diode? Draw V-I characteristic curve of zener diode. Explain its use as
a voltage regulator.
35. Discuss the variation of resistance with temperature with an expression and a graph.
36. What is ground wave communication? On what factors does the maximum range of
propagation in this mode depend?
37. Write the functions of the following in communication systems:
(i) Transducer
(ii) Repeater
38. Write two application of GPS.
39. By what percentage will the transmission ranges of TV tower be affected when the
height of the tower is increased by 21%?
40. Write briefly any two factors which demonstrate the need for modulating a signal.
Draw a suitable diagram to show amplitude modulation using a sinusoidal signal as
the modulating signal.
41. Mention three different modes of propagation used in communication system. Explain
with the help of a diagram how long distance communication can be achieved by
ionospheric reflection of radio waves.
42. A 25 mF capacitor, a 0.10 H inductor and a 25 ohm resistor are connected in series
with an AC source whose emf is given by ε = 310 sin 314 t volt.
(i) What is the frequency of the emf ? ( 50 Hz)
(ii) What is the reactance of the circuit ? ( 95.9 Ω capacitive )
(iii) What is the impedance of the circuit ? ( 99.1 Ω )
(iv) What is the current of the circuit ? ( 2.22 A)
(v) What is the phase angle of the current by which it leads or lags the applied emf ?
( tanφ = 3.84 )
(vi) What is the value of instantaneous value of current in the circuit ? ( I = 3.13 sin (
314t + 1.31 )
(vi) What are the effective voltage across the capacitor, inductor and resistance ? (
282.6 V, 69.7 V , 55.5 V )
(vii ) What value of inductance will make the impedance of the circuit minimum ? ( XL
= XC which gives L = 0.405 H )
43. Explain the determination of the internal resistance of a cell using voltmeter.
44. State and explain Kirchoff’s laws for electrical networks.
45. (a) Define self inductance. Write its SI unit.
(b)Derive an expression for self inductance of a long solenoid of length l, cross
section area A having N number of turns.
46. State the condition for resonance to occur in a series LCR circuit and derive an
expression for the resonant frequency. Draw a plot showing the variation of peak
current (im) with frequency ofthe ac source used. Define the Q factor of the circuit.
47. (a)What are eddy currents? Write their two applications.
(b)Figure shows a rectangular
conducting loop PQRS in which
arm RS of length l is movable.
The loop is kept in a uniform
magnetic field B directed
perpendicular to the plane of the
loop. The arm RS is moved with
a uniform speed v. Deduce an
expression for
(i)emf induced across the rod
‘RS’
(ii)The external force required to
move the arm.
(iii)The power dissipated as heat.
48. (a)State Lenz’s law. Give one example to illustrate this law. ‘The Lenz’s law is a
consequence to the principle of conservation of energy’. Justify this statement.
(b)Deduce an expression for the mutual inductance of two long coaxial solenoids but
having different radii and different number of turns.
49. Draw a schematic diagram of a step up transformer. Explain its working principle.
Deduce the expression for the secondary to primary voltage in terms of the number
of turns in the two coils. In an ideal transformer , how is the ratio related to the
current in the two coils?
How is the transformer used in large scale transmission and distribution of electrical
energy over long distances?
50. State the working of an a.c. generator with the help of a lebelled diagram.
The coils of a.c. generator have N turns, each of area A, is rotated with a constant
angular velocity ‘ω’. Deduce the expression for the alternating emf generated in the
coil. What is the source of energy generation in this device.
51. Define resolving power of a compound microscope. How does the resolving power
of a compound microscope change when
(i)
Refractive index of the medium between the object and objective lens
increases?
(ii)
Wavelength of the radiation used is increased?