The process whereby a liquid turns spontaneously into vapour is called

The height at which the atmosphere ceases to exist is about 80km. If the atmospheric pressure on the ground is 760 mmHg, the pressure at a height of 20km above ground level is

If in a simple pendulum experiment, the length of the inextensible string is increased by a factor of four, its period is increased by a factor of

Which of the following is a characteristic of stationary waves?