41.

Three charged particles are initially in position-1. They are free to move and they come to position-2, after some time. Let U₁ and U₂ be the electrostatic potential energies in position-1 and 2 then

• U₁ = U₂

• U₂ $\ge$ U₁

• U₂ > U₁

• U₁ > U₂

In L-R circuit the current increases to three - fourth of its maximum value in 4s, then the time constant of the circuit is

• 2 log_e 2

• $\frac{4}{{\log }_{\mathrm{e}}2}$

• $\frac{2}{{\log }_{\mathrm{e}}2}$

• $\frac{{\log }_{\mathrm{e}}2}{2}$

1 Wb/m² is equal to

• 10⁴ G

• 10² G

• 10^-2 G

• 10^-4 G

The sensitiveness of a moving coil galvanometer can be increased by decreasing the

• number of turns in the coils

• area of the coil

• magnetic field

• couple per unit twist of the suspension

The material of wire of potentiometer is made of

• copper

• steel

• manganin

• aluminium

A potential difference V is applied at the ends of a copper wire of length l and diameter d. On doubling only d, drift velocity

• becomes two times

• becomes half

• does not change

• becomes one-fourth

A steady current of 5 A is maintained for 45 min. During this time it deposits 4.572 g of zinc at the cathode of a voltmeter. ECE of zinc is

• 3.38 × 10^-4 g/C

• 3.397 × 10^-4 g/C

• 3.384 × 10^-3 g/C

• 3.394 × 10^-3 g/C

The earth's magnetic induction at a certain point is 7 x 10^-5 Wb/m². This is to be annuled by the magnetic induction at the centre of a circular conducting loop of radius 5 cm. The required current in the loop is

• 0.56 A

• 5.6 A

• 0.28 A

• 2.8 A

An astronomical telescope has a large aperture to

• reduce spherical aberration

• have high resolution

• increase span of observation

• have low dispersion

Which of the following is more close to a black body?

• Black board paint

• Green leaves

• Black holes

• Red roses