Potentiometer

The potentiometer is a basic component of many digital devices. It is a variable resistor that is measured in ohms. A voltage is applied to the wiper of a potentiometer, and the resistance of the circuit is determined by the length of the wire leading to the wiper. There are four types of potentiometers:  Rotary potentiometer, Linear potentiometer, Mechanical potentiometer, Digital potentiometer. The potentiometer measures resistance, but not in the same way as other resistors. The voltage applied to a potentiometer causes electrons to flow as they resist the flow of current. This resistance is often measured in ohms, and it is proportional to how far you turn the knob. In other words, the higher the ohms, the higher the resistance.

What is a potentiometer?

The potentiometer is essentially a wire across which a cell is connected. In the simulated design, the long wire is cut into several pieces, and they are placed next to each other and connected at the ends with a thick metal strip. The current flowing through the wire can be adjusted by connecting a variable resistance (rheostat) to the circuit. The user can change the resistance for measuring the potential difference. The voltage across any two points in a circuit is the energy transferred to bring the source’s charge to the load. A current will start flowing in a circuit if there is a potential difference across the circuit.

The potentiometer is a device used for measuring the voltage of an unknown source. It works by comparing this voltage to a known voltage. It is used to determine the electromotive force (emf) and internal resistance of the given cell and to compare the emf of different cells. The comparative method is used to analyse the results of different scenarios and is more accurate in a potentiometer due to its specific purpose of measuring electrical potential.

Working principle of potentiometer

The potentiometer is a device that works on the principle that the drop in voltage across any circuit element will be directly proportional to the length of the wire, provided the wire is of the uniform cross-sectional area, and the current flowing through the wire is uniform. 

Types of potentiometer

A potentiometer is basically of four types:

1. Rotary potentiometer
2. Linear potentiometer
3. Mechanical potentiometer
4. Digital potentiometer

5. Rotary potentiometer

A rotatory potentiometer is a three-terminal rotary encoder with two or four rotors that are capable of converting rotary motion into voltage outputs.

1. Linear potentiometer

The linear potentiometer is the most basic type of potentiometer. It’s made up of two resistors, usually in the 10k–100k range, that are connected to a single output. When you turn the knob, you’re changing the resistance of the two resistors, which changes the output voltage. 

1. Mechanical potentiometer

A mechanical potentiometer is a variable resistor with a wiper that can be adjusted to change the resistance of the circuit. The resistance of a potentiometer can be adjusted by turning a knob on the device, or by turning the wiper on or off. 

1. Digital potentiometer

Digital potentiometers (DP) offer a variety of benefits over traditional potentiometers, including reduced noise, improved resolution, and the ability to scale the potentiometer’s resolution to the resolution of the display or printer. 

Comparison of EMF of two cells 

A potentiometer consists of an electrical mechanism that is used to evaluate the amount of EMF between two cells. It is also used to calculate the internal resistance of the cell and the potential difference across a resistor. The EMFs of two cells can be compared by using the sum and difference method.

Sum method

When you have two electrical cells connected to each other in the way that a cell’s positive terminal is connected to the negative terminal of the other cell. The EMF of both the cells is added up and the EMF of the combination of both the cells is E1 + E2. This method of connecting two different electrical cells is called the sum method. 

Difference method

When two electrical cells are connected in an electrical circuit in such a way that their negative terminals, as well as positive terminals, are connected, then they oppose each other, and the effective EMF of the two cells is E1 – E2. This particular procedure is known as the difference method.

Potentiometer Sensitivity

The sensitivity of a potentiometer is the smallest variation in the potential that is calculated using a potentiometer. Its sensitivity usually depends upon the value of the potential gradient. When the value of the potential gradient is low, the potential difference calculated by a potentiometer is limited, and hence the sensitivity in the potentiometer is greater, meaning the smaller the potential difference, the more sensitive the potentiometer is. For a given amount of dissimilarity in the potential, the potential sensitivity can be multiplied in magnitude via the increased length of the potentiometer. The potentiometer sensitivity can also be higher for the following reasons: 

1. If the length of the potentiometer is increased.
2. If the flow of the current through a circuit decreases through the rheostat.

Measurement of Internal resistance of the cell

Internal resistance refers to the opposition to the flow of current offered by the cells and batteries themselves, which results in the generation of heat and heat buildup within the batteries themselves. The internal resistance of a battery is measured in Ohms.

The measurement of Internal resistance of the cell relationship between internal resistance and EMF of a cell is given by:

e = I (r + R)

Or  e = V + Ir

V is the potential difference (also known as the voltage) across the cell, which is the amount of energy the cell can provide when the current (I) is flowing through the circuit.

Conclusion

The potentiometer is a device that measures resistance. The resistance of a potentiometer is determined by the angle of a movable contact arm inside the potentiometer. The closer the arm is to the ends of the shaft, the higher the resistance. The closer the arm is to the middle of the shaft, the lower the resistance. It is of four types: Rotary potentiometer, Linear potentiometer, Mechanical potentiometer, Digital potentiometer. There are two methods for comparing the EMF of two cells: the sum method and the difference method. The sensitivity of a potentiometer is the smallest potential variation in the potential that is calculated with the help of a potentiometer.