Electromagnetic Waves — Physics STD 12 Science — Question

When light propagates in vacuum there is an electric field and a magnetic field. These fields:

1. Are constant in time.
2. Have zero average value.
3. Are perpendicular to the direction of propagation of light.
4. Are mutually perpendicular.

The formula of torque due to electric dipole is:

Which among the following is the source of the magnetic field (magnetism)?

For harder X-rays:

A convex lens of focal length 0.5 m and concave lens of focal length 1 m are combined. The power of the resulting lens will be

(a) 1 D

(b) – 1 D

(c) 0.5 D

(d)  – 0.5 D

Magnetic permeability is maximum for

(a) Diamagnetic substance	(b) Paramagnetic substance
(c) Ferromagnetic substance	(d) All of these

Core of electromagnets are made of ferromagnetic material which has:

A small, conducting circular loop is placed inside a long solenoid carrying a current. The plane of the loop contains the axis of the solenoid. If the current in the solenoid is varied, the current induced in the loop is:

We can reduce eddy currents in the core of transformer

(a) By increasing the number of turns in secondary coil

(b) By taking laminated core

(c) By making step-down transformer

(d) By using a weak ac at high potential

In Maxwell's velocity distribution curve area under the graph: