POTENTIOMETER
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Potentiometer is a device which has infinite resistance and it does not draw
any current from the circuit.
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The potential difference (voltage) per unit length of the wire
is called potential gradient.
Potentiometer principle:
The potential difference between two points
on the wire is directly proportional to the length of the wire of uniform cross
section and the temperature of the wire remains constant.
Explanation:
A potentiometer
consists of a long wire AB of length L having uniform cross section area A and
resistance R.
As shown
in the figure, a cell of emf E having internal resistance r is connected across
AB.
When the
circuit is switched on, current I pass through the wire.
Current through AB,
..............(1)
Potential
difference across AB is
VAB
= IR ……………(2)
Form equation (1) equation (2) becomes
…..(3)
The
potential difference per unit length of the wire is,
……(4)
is
known as potential gradient along AB and is denoted by K. It remains constant
if E is constant
Consider
a point C on the wire at distance l from the point A
The
potential difference between A and C is VAC
Therefore,
·
The
potentiometer is used
to compare
emf of cells and to find internal resistance of the cell. Also it is applied in
voltage divider, audio controls and sensors.
·
Disadvantages or demerits of
potentiometer:
1. Potentiometer is not portable
2. Direct measurement of potential
difference or emf is not possible.
·
Advantages of a Potentiometer Over a Voltmeter:
1. Potentiometer is more sensitive than a voltmeter.
2. Used to measure a potential difference as
well as emf of a cell.
3. More accurate than voltmeter.
4. Least count of a potentiometer is much
better compared to that of a voltmeter.
·
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