51.
Light Emitting Diodes (LED) is used in fancy electronic devices such as toys emit

52.
Out of the following pairs, which one does not have identical dimension?

53.
Mercury is commonly used as a thermometric fluid rather than water because

54.
Optical fibre works on the

55.
Light from the star, Alpha Centauri, which is nearest to the earth after the sun, reaches the earth in

56.
Supersonic plane fly with the speed

57.
Mach number is used in connection with the speed of

58.
On a stationary sail boat, air is blown from a fan attached to the boat. The boat

59.
Rainbow is due to

60.
Stars which appear single to the naked eye but are double when seen through a telescope are