What is Relative error?

Relative error and

If f=x^2 , What is the relative error in f?

An ammeter is connected to measure the current intensity in a circuit with a resistance R. What relative error will be made if connection of the ammeter does not change the current intensity in the circuit? The voltage across the ends of the circuit is kept constant.

The voltage across a resistance R is determined using a voltmeter connected to its ends. What relative error will be made if the readings of the voltmeter are taken as the voltage applied before it was switched on ? The current intensity in the circuit is constant.

Show that the relative error in the volue of a sphere due to an error in measurement of radius is thhree times the relative error in radius.

Show that the relative error in the volume of a sphere, due to an error in measuring the diameter, is three times the relative error in the diameter.