Potentiometer—

A potentiometer is a device used to measure the potential difference between two points or the unknown emf.

Principle-

When a uniform current flows through a uniform wire the potential drop across any length is directly proportional to the length of the wire.

Construction-

A potentiometer consists of a long wire of uniform cross section which is fixed on a wooden board in the pieces of 1m each with the help of copper or brass strips. The two ends of the wire is connected to a battery and a rheostat. Since, the cross section of the wire is uniform, the potential is uniformly drop throughout the wire.

Potential Gradient—

Potential drop per unit length of a wire is called potential gradient.