Which of these is observed when air is pumped out of a discharge tube without lowering its pressure

Which of the following characteristics of a wave is used in the measurement of the depth of the Sea?

If the attraction of the sun is suddenly ceased, the earth would continue to move in a straight line making a tangent with the original orbit. This statement is derived from Newton's

Heat may be transferred by conduction, convection and radiation. By which of these methods does heat travel through vacuum?

The part of the human eye that does similar work as the diaphragm of a camera lens is the