Physics

Modern refrigerators usually use a refrigerant called HFC-134a (1,1,1,2-Tetrafluoroethane), which does not deplete the ozone layer, instead of Freon. Freon used to be the most common refrigerant till the 1980s; however, its use has declined since the 1990s because it comes under Chlorofluorocarbon (CFC). Ammonia was also used a a common refrigerant in old refrigerators. However, Freon still remains the most commonly used refrigerant. Hydrochlorofluorocarbon (HCFC), is a type of refrigerator coolant used in newer refrigerator models. The types used today include HFC-134a, HCFC-142b and HCFC-22.

Light is made up of photons, so it has some particle properties. In the photoelectric effect, light hits some material which absorbs it, and then ejects incident electrons. The reason that the photoelectric effect is evidence for the particle nature of light has to do with how materials absorb that light energy and then eject it in the form of electrons.

Bats are capable of avoiding obstacles that they encounter, even in complete darkness. This is because they emit ultrasound (high frequency sound) and analyse the echo produced when the sound hits objects on their path. Prey capture without the aid of echolocation by some bats is also described.

The time when the sun crosses the plane of the earth’s equator, making night and day of approximately equal length all over the earth and occurring about March 21 (vernal equinox, or spring equinox ) and September 22 (autumnal equinox).