﻿ A charge is distributed uniformly over a ring of radius a . Obt

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## CBSE Class 12 Physics Solved Question Paper 2016

1.

A point charge +Q is placed at point O as shown in the figure. Is the potential
difference VA – VB is positive, negative or zero?

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2. How does the electric flux due to a point charge enclosed by a spherical Gaussian surface get affected when its radius is increased?
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3. Write the underlying principle of a moving coil galvanometer.
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4. Why are microwaves considered suitable for radar systems used in aircraft navigation?
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5. Define 'quality factor' of resonance in a series LCR circuit. What is its SI unit?
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6. Two cells of emfs 1.5 V and 2.0 V,  having internal resistances 0.2 Ω and 0.3 Ω, respectively, are connected in parallel. Calculate the emf and internal resistance of the equivalent cell.
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# 7.A charge is distributed uniformly over a ring of radius 'a'. Obtain an expression for the electric intensity E at a point on the axis of the ring. Hence, show that for points at large distance from the ring, it behaves like a point charge.

Consider a ring of radius 'a' which carries uniformly distributed positive total charge Q.

To find: electric field due to a ring at a point P lying at a distance x from its centre along the central axis perpendicular to the plane of the ring.

As the charge is distributed uniformly over the ring, the charge density over the ring is,

The perpendicular component of electric field due to charge on the ring along the x-axis cancels each other out.

As there is same charge on both sides of the ring, the magnitude of the electric field at P due to the segment of charge dQ is given by,

dE = ke
Ex

1. At the centre (X = 0) , electric field is zero.

2. When x>> a, a can be neglected in the denominator.

Therefore,

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8.

a) Write the expression for the magnetic force acting on a charged particle moving with velocity v in the presence of magnetic field B.

b) A neutron, an electron and an alpha particle, moving with equal velocities, enter a uniform magnetic field going into the plane of paper, as shown. Trace their paths in the field and justify your answer.

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9.

i) Define mutual Inductance.

ii) A pair of adjacent coils has a mutual inductance of 1.5 H. If the current in one coil changes 20 A in 0.5 s, what is the change of flux linkage with the other coil?

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10. Two parallel-plate capacitors X and Y have the same area of plates and same separation between them. X has air between the plates, while Y contains a dielectric medium of

i) Calculate capacitance of each capacitor if the equivalent capacitance of the combination is 4
ii) Calculate the potential difference between the plates x and Y

iii) Estimate the ratio of electrostatic energies stored in x and Y
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