Practice MCQ Questions and answers on Physics-GK

51

Light Emitting Diodes (LED) is used in fancy electronic devices such as toys emit

A) X-rays B) ultraviolet light C) visible light D) radio waves

Discuss

Answer & Solution

Answer: Option C

Solution:

Light Emitting Diodes (LED) is used in fancy electronic devices such as toys emit visible light.

52

Out of the following pairs, which one does not have identical dimension?

A) Moment of inertia and moment of a force B) Work and Torque C) Angular momentum and Planck's constant D) Impulse and Momentum

Discuss

Answer & Solution

Answer: Option A

Solution:

Moment of inertia and moment of a force does not have identical dimension.

53

Mercury is commonly used as a thermometric fluid rather than water because

A) specific heat of mercury is less than water B) specific heat of mercury is more than water C) mercury has greater visibility than water D) density of mercury is more than the water

Discuss

Answer & Solution

Answer: Option C

Solution:

Mercury has greater visibility than water.

54

Optical fibre works on the

A) principle of refraction B) total internal reflection C) scattering D) interference

Discuss

Answer & Solution

Answer: Option B

Solution:

The optical fibre is a device which works on the principle of total internal reflection by which light signals can be transmitted from one place to another with a negligible loss of energy. Characteristics of Optical Fibre: It has a large bandwidth.

55

Light from the star, Alpha Centauri, which is nearest to the earth after the sun, reaches the earth in

A) 4.2 seconds B) 42 seconds C) 4.2 years D) 42 years

Discuss

Answer & Solution

Answer: Option C

Solution:

Light from the nearest star reaches the earth in 4.2 years. The closest star to Earth are three stars in the Alpha Centauri system.

56

Supersonic plane fly with the speed

A) less than the speed of sound B) of sound C) greater than the speed of sound D) of light

Discuss

Answer & Solution

Answer: Option C

Solution:

Vehicles that fly at supersonic speeds are flying faster than the speed of sound.

57

Mach number is used in connection with the speed of

A) sound B) aircraft C) spacecraft D) ships

Discuss

Answer & Solution

Answer: Option B

Solution:

Mach number is used in connection with the speed of aircraft.

58

On a stationary sail boat, air is blown from a fan attached to the boat. The boat

A) moves in opposite direction in which the air is blown B) does not move C) moves in the same direction in which air blows D) spins around

Discuss

Answer & Solution

Answer: Option B

Solution:

In this case air blown by the fan will try to push the sail boat in a certain direction. But at the same time due to Newton's third law of motion the fan will experience a force due to the air blown in a direction opposite to the direction in which the sail boat will experience the force due to the blown air. So, as a whole the system will be at rest and it will not move.

59

Rainbow is due to

A) absorption of sunlight in minute water droplets B) diffusion of sunlight through water droplets C) ionisation of water deposits D) refraction and reflection of sunlight by water droplets

Discuss

Answer & Solution

Answer: Option D

Solution:

A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured circular arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun.

60

Stars which appear single to the naked eye but are double when seen through a telescope are

A) novas and supernovas B) binaries C) asteroids D) quasars

Discuss

Answer & Solution

Answer: Option B

Solution:

They are single to naked eye because they are far from us. But, if we see with telescope We can observe that there are two or double stars.