Question

plz help to understand these

1) what is the difference between Resistance and resistivity?

2)what is variable resistance and why it is required?

3)what is rheostat?

Answer 1

1):

Resistance	Resistivity
Resistance is the obstruction offered in the flow of current by the wire.	It is the tendency of a substance to offer obstruction in the flow of current per unit length and per unit area.
It depends on material of the wire temperature of wire area of cross-section length of wire	It depends material of the wire. (It does not depend on length and area of cross-section as both of them are taken as one unit given in defination.)

2)

a variable resistor is able to have its electrical resistance adjusted. These devices are used when working with electrical circuitry because they help tocontrol voltage and/or currents. They specifically work with voltage and currents thatare a part of the circuit.

3)

A rheostat is a variable resistor which is used to control current. They are able to vary the resistance in a circuit without interruption. ... It uses only two connections, even when 3 terminals (as in a potentiometer) are present.