31.

If there were no atmosphere, the average temperature on earth surface would be

• lower

• higher

• same

• 0^°C

Assertion:  The alternating current lags behind the e.m.f. by a phase angle of  $\mathrm{\pi }$/2, when AC flows through an inductor. 

Reason:  The inductive reactance increases as the frequency of AC source decreases.

• 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:  A spark occur when the poles of a switch when the switch is opened.

Reason: Current flowing in the conductor produces magnetic field.

• 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 correct explanation of assertion

• If assertion is true but reason is false

• If both assertion and reason are false

Assertion:  X-rays can penetrate through the flesh but not through the bones. 

Reason:  The penetrating power of X-rays depends on voltage.

• 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: We cannot think of magnetic field configuration with three poles.

Reason: A bar magnet does exert a torque on itself to its own field.

• 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:  A bird perches on a high power line and nothing happens to the bird.

Reason:  The level of bird is very high from the ground.

• 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:  Inductance  coils  are  usually  made  of  thick copper wire. 

Reason:  Induced  current  is more  in  wire  having  less  resistance.

• 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:  When a radius of circular loop carrying current is doubled, its magnetic moment becomes four times.

Reason: Magnetic moment depends on area of the loop.

• 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: In the following circuit, emf is 2 V and internal resistance of the cell is I Ω and R= 1 Ω, then reading of the voltmeter is 1 V.

Reason:  V = E $-$ IR where  E = 2V, I = 2/2 = 1A

• 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:  A domestic electrical appliance, working on a three pin will continue working even  if the top pin is removed. 

Reason: The third pin is used only as a safety device.

• 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.