Electric Charges and Fields — Physics STD 12 Science — Question

The heating coils rating at 220 volt and producing 50 cal/sec heat are available with the resistances 55Ω,110 Ω, 220 Ω   and 440 Ω. The heater of maximum power will be of(a) 440 Ω(b) 220 Ω(c) 110 Ω(d) 55 Ω

A piece of copper and the other of germanium are cooled from the room temperature to 80 K, then which of the following would be a correct statement(a) Resistance of each increases(b) Resistance of each decreases(c) Resistance of copper increases while that of germanium decreases (d) Resistance of copper decreases while that of germanium increases

In any Bohr orbit of the hydrogen atom, the ratio of kinetic energy to potential energy of the electron is(a) 1/2(b) 2(c) -1/2   (d)  -2

If a body is charged by rubbing it, its weight

An electron is moving in the north direction. It experiences a force in vertically upward direction. The magnetic field at the position of the electron is in the direction of(a) East(b) West(c) North(d) South

The capacitance of a metallic sphere will be 1μF, if its radius is nearly(a) 9 km  (b) 10 m (c) 1.11 m (d) 1.11 cm

Select the correct statement (a) In a full wave rectifier, two diodes work alternately(b) In a full wave rectifier, two diodes work simultaneously(c) The efficiency of full wave and half wave rectifiers is same(d) The full wave rectifier is bi-directional.

When the current i is flowing through a conductor, the drift velocity is v. If  2i  current is flowed through the same metal but having double the area of cross-section, then the drift velocity will be(a) v/4(b) v/2(c) v  (d) 4v