41.In an electronic watch, the component corresponding to the pendulum of a pendulum clock is :

42.With which of the following intruments can a sailor in a submarine see the objects on the surface of sea ?

43.The blue colour of the water in the sea is due to :

44.Moon has no atmosphere because :

45.A crystal capable of absorbing a radiation and re-emitting it in the form of visible light, does so after a certain small time interval of excitation. This phenomenin is called :