(i) What is the science (physics concept) behind a stethoscope? What is the principle?
(ii) How will you make a child to understand the, Intensity of light or sound From Density without using formulae.

Explanation

(i) The principle behind a stethoscope is multiple reflections of sound. It consists of a long tube made of rubber or metal. When sound pulses pass through one end of the tube, the pulses gets concentrated to other other end due to several reflections on the inner surface of the tube. Using this the doctor hears the patient's heart beats as concentrated rays.
(ii) Density means the closeness of the particles. As the particles are closely packed. Density is more. For example we say Dense forest, it means the trees are closely packed so that even light cannot pass into. Density can be used for solid, liquid and gas. But intensity means closeness of the waves or lines of force. Where the waves or lines of force are closer together. Intensity is more for example laser is a hightly intesnsified beam we say. Because in single beam, it has more number of coherent waves, packed closer together. Intensity can be used for light or sound or heat or electric lines of force or magnetic lines of force.