Potentiometer Working - Definition, Types, Application, FAQs

A potentiometer is an instrument used to measure the EMF, resistance, and voltage. It works based on the principle of balancing potential differences without drawing electric current. A potentiometer gives highly accurate measurements. In this article, we are going to discuss what is potentiometer class 12, the working principle of potentiometer, potentiometer working, the internal resistance of a cell, types of potentiometer, and application of potentiometer.

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This Story also Contains

1. What is a Potentiometer Class 12?
2. Working Principle Of Potentiometer and Potentiometer Working
3. Internal Resistance of the Cell
4. Types of Potentiometer Based on Adjustment Mechanism
5. Types of Rotating Potentiometers
6. Types of Linear Potentiometer
7. Application of Potentiometer

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What is a Potentiometer Class 12?

In physics, a potentiometer is an instrument that is made up of three terminal resistors that have sliding or rotating contact that forms a voltage divider and this voltage driver is also adjustable. The potentiometer is used as the rheostat (also known as variable resistor) when it has two terminals that contain one end and a wiper. In short, these potentiometers are also called “pots”. The potentiometer diagram is given below.

Working Principle Of Potentiometer and Potentiometer Working

The potentiometer contains a long resistive wire L, and an EMF battery V. This voltage V is also called driver cell voltage. Consider a primary circuit that is connected to the emf cell. The other end of the circuit is connected to the G, galvanometer. This circuit is considered to be a secondary circuit.

The potentiometer working is based on the potential across the wire and the length of the wire which has a uniform area cross-section and constant current flow that shares a proportionality relation. In short, the principle behind the potentiometer working can be explained as the potential across the wire is directly proportional to the length of the wire. This can be expressed as

$$V=I R$$

Where I denotes the current flow, R denotes the total resistance of the circuit, V denotes the voltage

$$R=\frac{\rho L}{A}$$

$$V=I \frac{\rho L}{A}$$

Where,

• $\rho$ denotes the resistivity of the material
• $A$ is used to denote the area cross-section

When $\rho$ and area are constant, then $I$ current also becomes constant for the rheostat.

$$
K V=K L E
$$

And

$$\frac{L \rho x}{A}=K x$$

Where,

• $x$ refers to the length of the potentiometer wire
• $E$ refers to the low EMF of a cell
• $K$ is a constant

When the potential difference between the ends is zero, the galvanometer G shows null detection. This denotes that the flow of current in the circuit is also zero. Here, the x is considered to be the length of the null point. Now, unknown EMF is found from the following formula,

$$
E=K x=\frac{L \rho x}{A}
$$

As the EMF has two cells, consider $L_1$ to be the length of the null point of EMF cell $E_1$ and $L_2$ to be the length of the null point of EMF cell

$$
\frac{E_1}{E_2}=\frac{L_1}{L_2}
$$

Internal Resistance of the Cell

A cell having unknown resistance (r) is connected in series with a resistance box and key $K_2$. The wires are connected in parallel with the cell and resistance box. A galvanometer is connected. Open circuit EMF of the cell is measured when the $K_2$ is opened as there is no current in the circuit.

$$
E=k \cdot L_1
$$

When $K_2$ is closed, the current flows through the resistance box and internal resistance, hence terminal voltage is

$$
V=k \cdot L_2
$$

We know that $E=V+I r$

Substitute $I=\frac{V}{R}$, we get

$$
E=V+\frac{V}{R} \cdot r
$$

Solving for r,

$$
r=R \cdot\left(\frac{E}{V}-1\right)
$$

Substituting $\frac{E}{V}=\frac{L_1}{L_2}$ in the equation,

The internal resistance of the cell, $$
r=R \cdot\left(\frac{L_1}{L_2}-1\right)
$$

Types of Potentiometer Based on Adjustment Mechanism

Let us see the different types of potentiometers and also discuss them in detail.

• Slider potentiometer (also known as slide potentiometer):
  This type of potentiometer is adjustable by sliding the wiper in the right or left direction.
• Thumbwheel potentiometer(also known as thumb potentiometer):
  This type of potentiometer is adjustable with a small thumbwheel.
• Trimmer potentiometer (also known as trim potentiometer):
  This type of potentiometer is adjustable by the fine-tuning of some electric signals.

Types of potentiometers based on operation are linear potentiometers and rotating potentiometers.

Types of Rotating Potentiometers

• Concentric potentiometer
• Single turn potentiometer
• Servo potentiometer

Concentric potentiometer

Two different potentiometers are adjustable individually by the concentric shafts. These types of potentiometers are used as control volume in the radios of old cars.

Single-turn potentiometer

This type of potentiometer is adjustable up to 270 degrees with the help of a single rotation. These types of potentiometers are used to control the resolution in a single rotation.

Servo potentiometer

The Servo potentiometer can be adjusted by servo motors automatically. These types of potentiometers are used in the volume control of remote control audio equipment.

Types of Linear Potentiometer

• Multi-turn slide Potentiometer
• Slide Potentiometer
• Dual slide Potentiometer

Multi-turn slide Potentiometer

In the construction of a multi-turn slide Potentiometer, a spindle is used.

Slide Potentiometer

In the construction of the slide Potentiometer, the high-quality fader is used. This potentiometer is used to measure distance.

Dual slide potentiometer

Dual slide Potentiometers are used to control single and dual sliders which are connected in parallel.

Application of Potentiometer

• Linear and rotary Potentiometer is used in controlling the audio equipment to adjust the volume of the audio signals.

• The potentiometer in televisions is used to control the brightness of the picture, colour, and so on.

• The potentiometers are also used in motion control in position feedback devices like servo motors.

• The potentiometers used in transducers are used to design the displacement transducers.

• The potentiometers are used as control volume in the radios of old cars.

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