Question

If the length of a potentiometer wire is increased, the value of the previously obtained balance point will be:
A) Increase
B) Decrease
C) Remains unchanged
D) Becomes 2 times

Answer 1

Hint
You need to see how the potential gradient relates to the length of the wire. We will then use this information to find the effect on the balance point from the potential gradient.

Complete step by step answer
A potentiometer is a three-terminal resistor that uses a sliding or rotating contact to form an adjustable voltage divider. It is used to control the voltage output for a given circuit. In a potentiometer, potential gradient is defined as:
${\text{PG}}\,{\text{ = }}\,\dfrac{{{\text{change}}\,{\text{in}}\,{\text{potential}}}}{{{\text{length}}\,{\text{of}}\,{\text{the}}\,{\text{wire}}}}$

From this we conclude that the potential gradient is inversely proportional to the length of wire. So if we increase this length, potential gradients will decrease. Balance point is the point on the wire where the potential is 0. This is done by the cancelling the potential in the wire with the potential at the tip of the contact. Now, as we already know that if a potential gradient of a potentiometer decreases, means there is a lower drop of potential for the same length of wire, so its balance point will shift forward to compensate for the lowering of potential.

So, the option with the correct answer is option A.

Note
Potential gradient of a potentiometer only depends on the total voltage across the wire and the length of the wire. It is however independent of the density of wire provided, the same potential difference is applied.