## Light Year

Light year by definition: It is the distance that light covers in one year when it travels.

The speed of light is approx. 186,282 miles per second. So it is 670615200 mile per hour and 16094764800 miles per day and at last 5874589152000 miles per year.

## List of Contents – Physics and Mechanics

1. Light
2. Light Year
3. Atmospheric air pressure
4. Why temperature drops as altitude increase?
5. Why 273 Kelvin is used for temperature conversion?

## Atmospheric air pressure

Atmospheric pressure is simply the weight of air molecules present above the measuring point. Air molecules have mass. Bar is one of the units of pressure. Pressure is actually the force acting per unit area. Here is the conversion.

1 N/m2 = 1 Pascal
100,000 Pascal = 1 bar

Light is a electromagnetic radiation. It travels in wave form with infinite number of energy pockets called “photons”. As we all know, a wave form has amplitude, frequency and wave length as its main parameters.

The speed of all electromagnetic radiation or EM waves in vacuum is 299,792,458 meters per second. So no matter what the parameters are, if waves start from a point at a time, they will reach the other point at the same time.

## What is Kelvin and Why 273 Kelvin is used for temperature conversion

Celsius, Fahrenheit and Kelvin are the units for measuring temperature. A temperature value can be expressed in any one or all of the above units independently. The values can be converted from one unit to other unit still keeping the meaning same.

We use the number 273 (273.15 exactly) to convert from Celsius to Kelvin and vice versa.