Ray Optics and Optical Instruments — Physics STD 12 Science — Question

The current flowing in a coil of self inductance 0.4 mH is increased by 250 mA in 0.1 sec. The e.m.f. induced will be

(a) + 1 V

(b) – 1 V

(c) + 1 mV

(d) – 1 mV

An element X has mass number 10, and number of neutrons = 7. Then what will be the number of proton?

Time period in vibration magnetometer will be infinity at

(a) Magnetic equator

(b) Magnetic poles

(c) Equator

(d) At all places

Lenz's law gives:

The ratio of the speed of the electrons in the ground state of hydrogen to the speed of light in vacuum is

(a) 1/2

(b) 2/137

(c) 1/137

(d) 1/237

Light wave is travelling along y-direction. If the corresponding   vector at any time is along the x-axis, the direction of   vector at that time is along

(a) y-axis

(b) x-axis

(c) + z-axis

(d) – z axis

A proton is about 1840 times heavier than an electron. When it is accelerated by a potential difference of 1 kV, its kinetic energy will be

(a) 1840 keV

(b) 1/1840 keV

(c) 1 keV

(d) 920 keV

The alternating voltage induced in the secondary coil of a transformer is mainly due to

(a) A varying electric field	(b) A varying magnetic field
(c) The vibrations of the primary coil	(d) The iron core of the transformer

If two bulbs of wattage 25 and 100 respectively each rated at 220 volt are connected in series with the supply of 440 volt, then which bulbs will fuse

(a) 100 watt bulb

(b) 25 watt bulb

(c) None of them

(d) Both of them

An electric current i enters and leaves a uniform circular wire of radius a through diametrically opposite points. A charged particle q moving along the axis of the circular wire passes through its centre at speed v. The magnetic force acting on the particle when it passes through the centre has a magnitude: