Saturday, March 22, 2008

JEE Past Objective Questions -Electricity - 1

1983 Screening

1. A hollow metal sphere of radius 5 cm is charged such that the potential on its surface is 10 Volts. The potential at centre of the sphere is

a) zero b) 10 V
c) same as at a point 5 cm away from the surface
d) same as at a point 25 cm away from the surface

Answer (b) 10 V

Reason: for a hollow metallic charged sphere the potential inside the sphere is constant and is equal to the potential at the surface.

See HC Verma page 135 point (f)
The electric potential due to a uniformly charged thin spherical shell at an internal point is the same everywhere and is equal to that at the surface.

2. Write the whether the statement is true or false. give brief reasons in support of your answer

Two identical metallic spheres of exactly equal masses are taken. One is given positive charge Q and the other an equal negative charge. Their masses after charging are different.

Answer: True
Reason: giving positive charge to a body involved removal of electrons. giving negative charge involves addition of electrons.