## A student studies that speed of light in air is 300000 kms

A student studies that speed of light in air is 300000 kms/ sec where that of speed in aglass slab is about 197000 kms/ sec. What causes the difference in speed of light in these two media?

**Answer:**

density of the medium…….

Important Points:

**Speed**: Speed is defined as the rate of change of position of an object in any direction.

CGS system | cm.s^{-1} |

SI system | ms^{-1} |

The mathematical representation of speed is:

Speed=Distance / Time

## Types of Speed

There are four types of speed and they are:

- Uniform speed
- Variable speed
- Average speed
- Instantaneous speed

**Uniform speed:** A object is said to be in uniform speed when the object covers equal distance in equal time intervals.

**Variable speed:** A object is said to be in variable speed when the object covers a different distance at equal intervals of times.

**Average speed:** Average speed is defined as the uniform speed which is given by the ratio of total distance travelled by an object to the total time taken by the object.

**Instantaneous speed:** When an object is moving with variable speed, then the speed of that object at any instant of time is known as instantaneous speed.