Electromagnetic Waves — Physics STD 12 Science — Question

A transformer is employed to

(a) Obtain a suitable dc voltage	(b) Convert dc into ac
(c) Obtain a suitable ac voltage	(d) Convert ac into dc

In a head-on elastic collision of two bodies of equal masses:

1. The velocities are interchanged.
2. The speeds are interchanged.
3. The momenta are interchanged.
4. The faster body slows down and the slower body speeds up.
5. All of the above.

The momentum of photon is :

An electric bulb rated for 500 watts at 100 volts is used in a circuit having a 200-volt supply. The resistance R that must be put in series with the bulb, so that the bulb draws 500 W is

(a) 10 Ω

(b) 20 Ω

(c) 50 Ω

(d) 100 Ω

When the angle of incidence on a material is 60°, the reflected light is completely polarized. The velocity of the refracted ray inside the material is (in ms^–1)

(a) 3

(b)

(c)

(d) 0.5

Two long parallel wires P and Q are both perpendicular to the plane of the paper with distance 5 m between them. If P and Q carry current of 2.5 amp and 5 amp respectively in the same direction, then the magnetic field at a point half way between the wires is

(a)

(b)

(c)

(d)

In a radioactive decay, neither the atomic number nor the mass number changes. Which of the following would be emitted in the decay process

(a) Proton

(b) Neutron

(c) Electron

(d) Photon

The figure shows three circuits with identical batteries, inductors, and resistors. Rank the circuits according to the current through the battery (i) just after the switch is closed and (ii) a long time later, greatest first

(a) (i)  (ii)

(b) (i)   (ii)

(c) (i)  (ii)

(d) (i)  (ii)

Two identical thin bar magnets each of length l and pole strength m are placed at right angle to each other with north pole of one touching south pole of the other. Magnetic moment of the system is

(a) ml

(b) 2ml

(c)

(d)