Physics

Tap water is placed in an open pad and allowed to evaporate. After some time the temperature of water decreases slightly.

Hydroscope is an optical device for enabling a person to see an object at a considerable distance below the surface of water by means of a series of mirrors enclosed in a steel tube. Hydrophone is an instrument used for recording sound under water. It is the underwater equivalent of a microphone that measures pressure fluctuations, and these are usually converted to sound pressure level (SPL), a logarithmic measure of the mean square acoustic pressure.

X-rays and gamma rays are photons, i.e. high energy light-waves. When emitted by a source, for example, radium or cobalt, located outside the body, they easily pass through the body, hence they are usually called penetrating radiation. Because X-rays are penetrating, they can be used in diagnostic medicine to image human bones or human organs made opaque by a dye.

The ”Greenhouse effect’ is mainly due to increase in atmospheric carbon dioxide.

One parsec is the distance to an object whose parallax angle is one arcsecond. The radius of the Earth’s orbit equals one astronomical unit (AU), so an object that is one parsec distant is 206,265 AU (or 3.26 light-years) away.