Physics

The Hooke’s law is valid only when the stress is proportional to the strain, that is only in the proportionality limit.

Number of lattices in the orthorhombic system is 7.

In the late of 17th century British scientist Isaac Newton studied cooling of bodies. Experiments showed that the cooling rate is approximately proportional to the difference of temperatures between the heated body and the environment. This fact can be written as the differential relation : dQ dt A T T S= abg, where A is the surface area of the body through which the heat is transferred, T is the temperature of the body, TS is the temperature of the surrounding environment, á is the heat transfer coefficient depending on the geometry of the body, state of the surface, heat transfer mode, and other factors. Surface area or volume ratio is an important influence on temperature control. For same volume sphere has minimum surface area, while circular plate has maximum surface area. So sphere cools slowest and plate cools fastest.

Light year is the unit of Astronomical distance.

The lux (symbol: lx) is the SI unit of illuminance and luminous emittance. It is used in photometry as a measure of the intensity of light, with wavelengths weighted according to the luminosity function, a standardized model of human brightness perception.

They usually appear as swift-moving black clouds, often approaching from the northwest southwest, south or west at speeds of 25-35 knots. You can determine the distance of an approaching thunderstorm by counting the number of seconds between the lightning flash and the thunder clap, and dividing by five.

In a optical fibre cable, the signal is propagated along the inner core.

X-rays – smaller than 10 nano metre. Gamma- rays – 0.0005 to 0.1 nano metre. Alpha-rays – 125 nano metre.

In physics, power is the rate of doing work. It is the amount of energy consumed per unit time. The unit of power is the joule per second (J/s), known as the watt.

The primary reason that power is transmitted at high voltages is to increase efficiency. As electricity is transmitted over long distances, there are inherent energy losses along the way.