If the distance between two charges is halved, then the force between them becomes

To increase the magnifying power of a telescope, the focal length of

An object moving around in a circle is moving with

Which of the following pairs is incorrect?

The force of gravity on the moon is

A transformer is used to

When milk is churned, the cream from it is separated due to

The element used in an electric filament is

The sky is blue in colour due to

Velocity of sound is minimum in

During rusting

When water boils, its temperature

The terminal colours of the rainbow are

The colour of the ocean appears to be blue because the sunlight falling on it is

A person is sitting facing the engine in a moving train. He tosses a coin. The coin falls behind him. This shows that the train is