If the emf of the driving cell be decreased. What will be effect on the position of zero deflection in a potentiometer.?

When the electromotive force (emf) of the driving cell in a potentiometer is decreased, it has a direct impact on the position of zero deflection. To understand this, let’s break down the concepts involved and how they relate to the operation of a potentiometer.

Understanding Potentiometer Basics

A potentiometer is an instrument used to measure the potential difference (voltage) across two points in a circuit. It operates on the principle of balancing the voltage across a known length of wire with the voltage of an unknown source. The key component here is the driving cell, which provides a constant emf to create a potential gradient along the wire.

Effect of Decreasing the EMF

When the emf of the driving cell is decreased, the overall potential difference across the potentiometer wire also decreases. This change affects the potential gradient along the wire, which is defined as the voltage per unit length. A lower emf means that for the same length of wire, there is less voltage available.

Position of Zero Deflection

The zero deflection point in a potentiometer is where the potential difference across the wire equals the potential difference of the unknown voltage being measured. If the emf of the driving cell is reduced, the potential gradient decreases, meaning that the same voltage will now occupy a longer length of wire. As a result, the position where the unknown voltage balances with the potential difference along the wire will shift.

• If the unknown voltage remains constant, the zero deflection point will move towards the end of the wire.
• This shift occurs because the lower emf means that it takes a longer length of wire to achieve the same voltage drop that was previously achieved with a higher emf.

Illustrative Example

Imagine a potentiometer wire that is 10 meters long, with a driving cell providing 10 volts. This gives a potential gradient of 1 volt per meter. If you have an unknown voltage of 5 volts, the zero deflection point would be at 5 meters along the wire. Now, if the emf of the driving cell is decreased to 5 volts, the potential gradient becomes 0.5 volts per meter. To find the new zero deflection point for the same 5-volt unknown, you would need to travel 10 meters along the wire (5 volts / 0.5 volts per meter), which means the zero deflection point would now be at the end of the wire.

Conclusion

In summary, decreasing the emf of the driving cell in a potentiometer results in a shift of the zero deflection point towards the end of the wire. This shift occurs because the potential gradient is reduced, requiring a longer length of wire to balance the same voltage. Understanding this relationship is crucial for accurately using a potentiometer in various electrical measurements.