Current Electricity — Physics STD 12 Science — Question

Electrostatic potential is ______ throughout the volume of the conductor and has _____ value on its surface.

An object placed 10 cm in front of a lens has an image 20 cm behind the lens. What is the power of the lens (in dioptres)

(a) 1.5

(b) 3.0

(c) – 15.0

(d) + 15.0

A magnet is brought towards a coil (i) speedly (ii) slowly then the induced e.m.f./induced charge will be respectively

(a)  More in first case / More in first case

(b)  More in first case/Equal in both case

(c)  Less in first case/More in second case

(d)  Less in first case/Equal in both case

In a cathode ray oscillograph, the focusing of beam on the screen is achieved by:

A particle of charge q and mass m moving with a velocity v along the x-axis enters the region x > 0 with uniform magnetic field B along the   direction. The particle will penetrate in this region in the x-direction upto a distance d equal to

(a) Zero

(b)

(c)

(d) Infinity

Two coherent sources of different intensities send waves which interfere. The ratio of maximum intensity to the minimum intensity is 25. The intensities of the sources are in the ratio

(a) 25 : 1

(b) 5 : 1

(c) 9 : 4

(d) 25 : 16

A photoelectric cell is a device which?

The electrons are emitted in the photoelectric effect from a metal surface         

(a) Only if the frequency of the incident radiation is above a certain threshold value

(b) Only if the temperature of the surface is high

(c) At a rate that is independent of the nature of the metal

(d) With a maximum velocity proportional to the frequency of the incident radiation

 electrons reach the anode per second. If the power consumed is 448 milliwatts, then the plate (anode) voltage is

(a) 150 V

(b) 200V

(c) 14 × 448 V

(d) 448/14V