Class 12 Physics 2020 Board Exam

If the net electric flux through a closed surface is zero, then we can infer
(A) no net charge is enclosed by the surface.
(B) uniform electric field exists within the surface.
(C) electric potential varies from point to point inside the surface.
(D) charge is present inside the surface.

A cell of internal resistance r connected across an external resistance R can supply maximum current when
(A) R = r
(B) R > r
(C) R = r/2
(D) R = 0

Resistivity of a given conductor depends upon
(A) temperature.
(B) length of conductor.
(C) area of cross-section.
(D) shape of the conductor.

For a fixed potential difference applied across a conductor, the drift speed of free electrons does not depend upon
(A) free electron density in the conductor.
(B) mass of the electrons.
(C) length of the conductor.
(D) temperature of the conductor.

An electric dipole consisting of charges + q and - q separated by a distance L is in stable equilibrium in a uniform electric field E. The electrostatic potential energy of the dipole is
(A) qLE
(B) zero
(C) -qLE
(D) -2qEL

In a current carrying conductor, the ratio of the electric field and the current density at a point is called
(A) Resistivity
(B) Conductivity
(C) Resistance
(D) Mobility

Ohm's law is obeyed by
(A) extrinsic semiconductors.
(B) intrinsic semiconductors.
(C) metals at low temperature.
(D) metals at high temperature.

A potentiometer can measure emf of a cell because
(A) the sensitivity of potentiometer is large.
(B) no current is drawn from the cell at balance.
(C) no current flows in the wire of potentiometer at balance.
(D) internal resistance of cell is neglected.

An electron is released from rest in a region of uniform electric and magnetic fields acting parallel to each other. The electron will
(A) move in a straight line.
(B) move in a circle.
(C) remain stationary.
(D) move in a helical path.

The resolving power of a telescope can be increased by increasing
(A) wavelength of light.
(B) diameter of objective.
(C) length of the tube.
(D) focal length of eyepiece.