Physics

When a liquid is heated, its volume increases and mass of liquid being same density decreases.

A nanosecond (ns) is an SI unit of time equal to one billionth of a second.

The term photon refers to sub atomic particle.

Betatron is preferred for accelerating electrons.

The red colour in the sky at sunset (and sunrise) is due to an effect called Rayleigh scattering. At sunrise or sunset, since the Sun is low on the horizon, the light rays must pass through more of the atmosphere – and therefore bounce off more molecules – than at other times of day. Thus, blue light gets scattered away before the light reaches your eyes. Other colors – such as red, orange and yellow –continue to pass through the atmosphere unaffected.

Loudness is a subjective characteristic of a sound (as opposed to the sound-pressure level in decibels, which is objective and directly measurable). Perceived loudness of sound is a psycho-acoustic quantity that depends on sound pressure level, the frequency spectrum, and the time behavior of the sound in question. The sone is a unit of perceived loudness that was proposed by Stanley Smith Stevens in 1936.Being a unit of how loud a sound is perceived, the sone scale of loudness is based on data obtained from subjects who were asked to judge the loudness of pure tones and noise. One sone is arbitrarily set equal to the loudness of a 1,000-hertz tone at a sound level of 40 decibels (Encyclopedia Britannica).

Concave mirrors are used in search lights and torches so that we have a more focused light beam which will not diverge out and hence help in searching. It is used for different light rays falling on it to a single point.

Atmospheric pressure is caused by the gravitational attraction of the planet on the atmospheric gases above the surface, and is a function of the mass of the planet, the radius of the surface, and the amount and composition of the gases and their vertical distribution in the atmosphere.