# Using Potentiometer to find balancing emf.

• harjyot
In summary, when the potentiometer is balanced, the high resistance does not affect the null point and can be replaced with a short circuit without changing anything.
harjyot
According to my book, if we connect a high resistance in series to the secondary cell (whose emf is to be balanced) , connect this whole apparatus to a potentiometer with an auxiliary Emf and find the null point . It's written that even after removing the Hugh resistance the null point comes down to be the same. How's that ? Doesn't the High resistance In fact contribute to increase the effective balancing length? Or do we assume that the potential gradient of the potentiometer far exceeds the potential drop created by the resistance?

I would have been nice to have a circuit showing what you mean. My guess is that when in balance there is no voltage drop across the "high resistance". So no current flowing through it which means it can be replaced with a short circuit without anything changing.

harjyot said:
According to my book, if we connect a high resistance in series to the secondary cell (whose emf is to be balanced) , connect this whole apparatus to a potentiometer with an auxiliary Emf and find the null point . It's written that even after removing the Hugh resistance the null point comes down to be the same. How's that ? Doesn't the High resistance In fact contribute to increase the effective balancing length? Or do we assume that the potential gradient of the potentiometer far exceeds the potential drop created by the resistance?

When the potentiometer is balanced, there is no current through the series 'protection' resistor so there is no voltage drop across it and the reference cell voltage also appears on the slider of the pot.

## 1. How does a potentiometer work?

A potentiometer is an electrical component that is used to measure or control voltage. It consists of a resistive element, usually a long wire or strip, with three terminals. By connecting the two outer terminals to a voltage source and the third terminal to a voltmeter, the voltage drop across the resistive element can be measured.

## 2. What is balancing emf?

Balancing emf is the voltage at which the resistive element of a potentiometer is perfectly balanced. In other words, the voltage drop across the resistive element is equal to the voltage being measured. This point is used to determine the unknown voltage by adjusting the position of the sliding contact on the potentiometer.

## 3. How is a potentiometer used to find balancing emf?

To find balancing emf, the potentiometer is first connected to a known voltage source and a voltmeter. The sliding contact is then moved along the resistive element until the voltmeter reads zero. This indicates that the voltage drop across the resistive element is equal to the known voltage, and the balancing emf can be calculated by measuring the distance from the sliding contact to the end of the resistive element.

## 4. What are the advantages of using a potentiometer to find balancing emf?

One advantage of using a potentiometer is that it provides a more precise measurement compared to other methods. It also allows for a wide range of voltages to be measured with a single instrument. Additionally, potentiometers are relatively inexpensive and easy to use.

## 5. Are there any limitations when using a potentiometer to find balancing emf?

Yes, there are some limitations. Potentiometers are sensitive to external factors such as temperature and humidity, which can affect the accuracy of the measurement. They also require a known voltage source to be connected, which may not always be available. Additionally, the resistive element of a potentiometer can wear out over time, leading to less accurate readings.

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