Moving Charges and Magnetism — Physics STD 12 Science — Question

The speeds of microwaves, infrared waves, and ultraviolet waves are V_m, V_i, and V_u respectively. Identify the correct combination showing the different waves in vacuum.

If a source is transmitting electro-magnetic waves of frequency 8.196×10⁶Hz, then the wavelength of the electro-magnetic waves transmitted from the source will be:

A varying current at the rate of 3 A/s in a coil generates an e.m.f. of 8 mV in a nearby coil. The mutual inductance of the two coils is

(a) 2.66 mH

(b) 2.66

(c) 2.66 H

(d) 0.266 H

A power transformer is used to step up an alternating e.m.f. of 220 V to 11 kV to transmit 4.4 kW of power. If the primary coil has 1000 turns, what is the current rating of the secondary ? Assume 100% efficiency for the transformer

(a) 4 A

(b) 0.4 A

(c) 0.04 A

(d) 0.2 A

In the adjoining figure, four capacitors are shown with their respective capacities and the P.D. applied. The charge and the P.D. across the 4μF  capacitor will be

(a) 600 μC; 150 volts

(b) 300 μC; 75 volts

(c) 800 μC; 200 volts

(d) 580 μC; 145 volts

In determining the temperature of a distant star, one makes use of

(a) Kirchhoff's law	(b) Stefan's law
(c) Wien's displacement law	(d) None of these

The potential gradient at which the dielectric of a condenser just gets punctured is called:

In cyclotron the resonance condition is:

Two parallel beams of electrons moving in the same direction produce a mutual force

(a) Of attraction in plane of paper

(b) Of repulsion in plane of paper

(c) Upwards perpendicular to plane of paper

(d) Downwards perpendicular to plane of paper

If a small amount of antimony is added to germanium crystal: