Current Electricity — Physics STD 12 Science — Question

Gauss's law is valid for:

In Bohr model of hydrogen atom, the ratio of periods of revolution of an electron in n = 2  and n = 1 orbits is

(a) 2 : 1

(b) 4 : 1

(c) 8 : 1

(d) 16 : 1

In a transistor, a change of 8.0 mA in the emitter current produces a change of 7.8 mA in the collector current. What change in the base current is necessary to produce the same change in the collector current

(a) 50 mA

(b) 100 mA

(c) 150 mA

(d) 200 mA

A metal surface of work function 1.07 eV is irradiated with light of wavelength 332 nm. The retarding potential required to stop the escape of photo-electrons is

(a) 4.81 eV

(b) 3.74 eV

(c) 2.66 eV

(d) 1.07 eV

When moving electron comes closer to other stationary electron, then its kinetic energy and potential energy respectively _____ and _____.

Two short magnets having magnetic moments in the ratio 27 : 8, when placed on opposite sides of a deflection magnetometer, produce no deflection. If the distance of the weaker magnet is 0.12 m from the centre of deflection magnetometer, the distance of the stronger magnet from the centre is

(a) 0.06 m

(b) 0.08 m

(c) 0.12 m

(d) 0.18 m

For a normal eye, the least distance of distinct vision is

(a) 0.25 m

(b)  0.50 m

(c) 25 m

(d)  Infinite

In the following circuit, the bulb will become suddenly bright if

(a) Contact is made or broken	(b) Contact is made
(c) Contact is broken	(d) Won't become bright at all

A photon of energy 3.4 eV is incident on a metal having work function 2 eV. The maximum K.E. of photo-electrons is equal to

(a) 1.4 eV

(b) 1.7 eV

(c) 5.4 eV

(d) 6.8 eV

The equivalent resistance of resistors connected in series is always

(a) Equal to the mean of component resistors

(b) Less than the lowest of component resistors

(c) In between the lowest and the highest of component resistors

(d) Equal to sum of component resistors