Current Electricity — Physics STD 12 Science — Question

Two radioactive materials  and  have decay constants 10λ  and λ respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of   to that of   will be 1/e  after a time

(a) 1/(10 λ)

(b) 1/(11 λ)

(c) 11(10 λ)

(d) 1(9 λ)

A conducting square loop of side L and resistance R moves in its plane with a uniform velocity v perpendicular to one of its sides. A magnetic induction B constant in time and space, pointing perpendicular and into the plane of the loop exists everywhere. The current induced in the loop is

(a)  clockwise

(b) anticlockwise

(c) anticlockwise

(d) Zero

The conductivity of a semiconductor increases with increase in temperature because:

Half life of  is  5 days. If we start with 50,000  atoms of this isotope, the number of atoms left over after 10 days is

(a) 5,000

(b) 25,000

(c) 12,500

(d) 20,000

A combination of two thin lenses of the same material with focal lengths  and , arranged on a common axis minimizes chromatic aberration, if the distance between them is

(a)

(b)

(c) (

(d)

Current flowing through the ideal diode shown in the circuit is __________ .

A photon of  1.7  Joules is absorbed by a material under special circumstances. The correct statement is

(a) Electrons of the atom of absorbed material will go the higher energy states

(b) Electron and positron pair will be created

(c) Only positron will be produced

(d) Photoelectric effect will occur and electron will be produced

To obtain maximum EMF from a number of cells, they must be connected in.

A heater coil connected to a supply of a 220 V is dissipating some power  The coil is cut into half and the two halves are connected in parallel. The heater now dissipates a power  The ratio of power  is

(a) 2 : 1

(b) 1 : 2

(c) 1 : 4

(d) 4 : 1

In an ideal parallel LC circuit, the capacitor is charged by connecting it to a D.C. source which is then disconnected. The current in the circuit.