Physics

CBSE Class 12

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1.

A point charge +Q is placed at point O as shown in the figure. Is the potential

difference V_{A} – V_{B} 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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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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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 = k_{e}

E_{x} =

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

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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