State the principle used by a ballet dancer to increase his/her angular speed.

State the principle which Is used to find out current through galvanometer.

A company manufacturing PVC pipes claims in an advertisement that the volume of water flowing out through the pipe in a given time is as per the equation V=KA^2ut where A is the area of cross section of the pipe, u is the speed of flow, t is the time and K is a dimensionless constant. Name the principle that can be used to check the dimensional correctness of this equation.

A boy is riding a bicycle with Its dynamo on when he Increases the speed the brightness of the bulb connected to the dynamo increases.State the law used to explain the above phenomenon.