In case of linearly polarised light, the magnitude of the electric field vector

• does not change with time

• varies periodically with time

• increases and decreases linearly with time

• is parallel to the direction of propagation

Assertion:  The true geographic north direction is found by using a compass needle.

Reason: The impurities meridian of the earth is along the axis of rotation of the earth.

• If both assertion and reason are true and reason is the correct explanation of assertion

• If both assertion and reason are true but reason is not the correct explanation of assertion

• If assertion is true but reason is false

• If both assertion and reason are false

Assertion: There are very small sporadic changes in the period of rotation of the earth. 

Reason: Shi fling of large air masses in the earth's atmosphere produce a change in the moment of inertia of the earth causing its period of rotation to change.

• If both assertion and reason are true and reason is the correct explanation of assertion

• If both assertion and reason are true but reason is not the correct explanation of assertion

• If assertion is true but reason is false

• If both assertion and reason are false

The maximum distance upto which TV transmission from a TV of height h can be received is proportional to

• h^1/2

• h

• h³

• h²

35.

In short wave communication, waves of which of the following frequencies will be reflected back by the ionospheric layer having electron density 10¹¹ per  m³ ?

• 2 MHz

• 10 MHz

• 12 MHz

• 18 MHz

X-ray beam are affected by

• electric field

• magnetic field

• both (a) and (b)

• none of these

All components of the electromagnetic spectrum in vacuum have the same

• energy

• velocity

• wavelength

• frequency

The difference between soft and hard X-rays is of :

• velocity

• intensity

• frequency

• polarization

If v_g, v_x and v_m are the speeds of gamma rays, X rays and microwaves respectively in vacuum then :

• v_g > v_m > v_x

• v_g > v_x > v_m

• v_g = v_m = v_x

• none of these

The minimum wavelength of X-rays emitted by X-ray tube is 0.4125 Å. The accelerating voltage is :

• 30 kV

• 50 kV

• 80 kV

• 60 kV