Electricity & Megnetism

Difference between potentiometer and voltmeter in tabular form

Difference between potentiometer and voltmeterThe voltmeter is used to find the potential difference,it has high and finite resistance. While potentiometer has high and infinite resistance. More differences between potentiometer and voltmeter are given in the comparison table below.

Potentiometer Vs Voltmeter

VoltmeterPotentiometer
Its resistance is high and finiteIts resistance is high and  infinite
It draws some current from emf sourceIt does not draw any electric current from the source of  emf
 Potential difference measured by it is less

then the actual potential difference

Potential difference measured by it is equal to

actual potential difference

It has low sensitivityIt has high sensitivity
It is a versatile instrumentIt measures only emf or potential difference
It is based on the deflection methodIt is based on the zero deflection method

See also: Difference between galvanometer and ammeter

Potentiometer

The potentiometer is a device mainly used to measure the emf of a given cell and to compare emfs of cells. It is also used to measure the internal resistance of a given cell.

Circuit diagram of potentiometer

Potentiometer consists of a long resistive wire AB of length L (about 6m to 10

m long) made up of mangnine or constantan. A battery of known voltage e and internal resistance r called supplier battery or driver cell. Connection of these two forms a primary circuit.

One terminal of another cell (whose emf E is to be measured) is connected at one end of the main

circuit and the other terminal at any point on the resistive wire through a galvanometer G. This forms the secondary circuit.

Other details are as follows

J = Jockey

K = Key

R = Resistance of potentiometer wire,

r = Specific resistance of potentiometer wire.

Rh = Variable resistance which controls the current through the wire AB

(3) Points to be remember

(i) The specific resistance (r) of potentiometer wire must be high but its temperature coefficient of

resistance (a) must be low.

(ii) All higher potential points (terminals) of primary and secondary circuits must be connected

together at point A and all lower potential points must be connected to point B or jockey.

(iii) The value of the known potential difference must be greater than the value of the unknown potential

difference to be measured.

(iv) The potential gradient must remain constant. For this, the current in the primary circuit must

remain constant and the jockey must not be slided in contact with the wire.

(v) The diameter of the potentiometer wire must be uniform everywhere.

See also : Joules law

Sensitivity of potentiometer : A potentiometer is said to be

more sensitive if it measures a small potential difference more

accurately.

(i) The sensitivity of the potentiometer is assessed by its potential

gradient. The sensitivity is inversely proportional to the potential gradient.

(ii) In order to increase the sensitivity of potentiometer

(a) The resistance in the primary circuits will have to be decreased.

(b) The length of the potentiometer wire will have to be increased so that the length may be measured more

accurately.

Related topics :

Difference between ammeter and voltmeter

Difference between emf and potential difference

Difference between electric potential and potential difference

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