Electronics

Potentiometer Definition:

“A potentiometer is an electrical device that changes the resistance value to control the flow of current and also measures emf of a cell.”

A potentiometer, also known as ‘pot‘ is a passive and three-terminal device. Though pot and variable resistors (rheostats) seem to be the same device, they differ in their connections within a circuit. It is an electrical device rather an electronic device.

What does a potentiometer do?

A pot limits the current flow by providing resistance value. That means it can increase or decrease the current of a circuit. It also works as an adjustable voltage divider. Based on this functionality, a pot can measure the electrical emf also.

Examples: 1k resistor potentiometer, 10k potentiometer& 100k potentiometer

The ‘k’ represents kiloohms. The numeric value tells the value of resistance. 1k means that the pot will provide resistance up to 1000 ohm. 10k & 100k means it will provide ten times and 100 times more resistance than 1k, respectively. The lesser the resistance value, the more the current drawn by that pot. Similarly, a 500k pot means it has a resistance value between 0 to 500 kiloohm.

How does the potentiometer work?

Potentiometers have some basic working principles. A pot has two terminals as input (marked as red and green in the figure). The input voltage is applied – across the resistor. Then the output voltage is measured. It comes out as the difference between the fixed and moving contact. The wiper plays a vital role here. While optimizing the output voltage- as per the need, the wiper needs to be moved- along the resistive element. Moving the slider helps to balance the galvanometer in case of measuring the emf of a cell. Now it acts as a voltage divider as it continuously produces variable voltage. Based on this concept, a pot measures electrical emf.

How does a potentiometer work as a voltage divider?

When the pot’s slider is moved- to the right, that causes a fall in resistance, fall in resistance further causes a small voltage drop. After that, if the wiper is moved- to the left, the resistance value eventually gets increased. Noe, there is also a voltage drop, but this time it is more than the previous case. So we can conclude that the output voltage has a direct relationship with the position of the wiper. The voltage drop value is calculated -by subtracting from the source voltage.

Types of Potentiometers

Based on shape, there are mainly two types

They are –

• A. Linear pot.
• B. Rotary pot.

Linear potentiometer:

In this type of pot, the slider moves linearly. Some different types are –

Slider potentiometer or slide pot:

If the wiper moves, in left-right or up-down direction, to adjust the pot, then it is slide pot. Slide pots find its application in audio, where it is known as faders.

Dual slide pot:

If a single slider controls two pots at a time, then it is a dual-slide pot. It also finds application in audio controlling.

Motorized slide pot

If a servo motor controls a slide pot’s slider, the pot is called a motorized slide pot or motorized fader. It has applications in audio control, where automatic control is required.

B. Rotary Pot

In this type of pot, the slider moves circularly. Some different types are –

Single – turn pot:

In a rotary pot, if it takes a single turn to control the pot, this type of rotary pot is known as a single turn pot. It takes approximately 3π / 2 degrees.

Multi-turn pot:

This type of pot requires multiple rotations of the slider. It generally takes 5-6 turns. It provides high precision and controls, that is why it has application in calibration circuits.

Symbol of the potentiometer?

The symbol of a pot is a standard resistor symbol with an arrow. Note that a variable resistor or rheostat symbol is also a resistance symbol with an added arrow, but the arrow’s position differentiates the devices.  

Difference between rheostat and a potentiometer?

There is a misconception that a rheostat and a potentiometer are the same things, but there are some differences. Let us discuss some of them –

Subject of Comparison	Potentiometer	Rheostat
Number of Terminals	Three terminal device	Two terminal device
Connection in Circuit	Parallel connection	Series connection
Quantity Controlled	Controls Voltage	Controls Current
Application	Low power application	High power application
Number of Turns	Both single and multi-turn	Single turn
Resistive material	Materials like Graphite	Carbon disk, Constantan, Platinum, etc
Symbol

Frequently asked questions

1. What is the resistive element composed of a potentiometer?

The resistive element is the cause that a pot can offer resistance. Generally, Graphite is the material for making resistive elements. Sometimes they are also made of carbon materials, resistive wires, ceramic metal mixtures, etc.

2. What is a digital potentiometer?

A digital pot is a digital device. It performs the same task as an analog pot does. It has found application in microcontroller electronics.

3. What is a logarithmic potentiometer?

A logarithmic pot changes its resistance value logarithmically. It comes under the non-linear type.

4. What are the parts of a potentiometer?

A typical pot consists of – two fixed terminals and a moving terminal. It also has a resistive element. By using the two fixed terminals, potentiometers take the input. The other part is a wiper or slider.

5. Does a potentiometer reduce voltage?

No, a pot doesn’t change the voltage of the circuit. It only controls resistance.

6. What is a potentiometer knob?

A pot knob is a holder for the slider of a rotary pot. By rotating the knob, the resistance changes.

7. How to compare – the emf of two cells using a pot?

EMF or electromotive-force is a parameter of measuring energy. It is the reason behind the flow of current in a circuit. The potential difference between two points is referred- to as electromotive-force. Its unit is volt.

The mathematical formula is – e = E / Q, where q is the charge, and E is the energy. By using a pot, we can find the emf of a cell. We need to find out the balancing length, where the galvanometer deflection is nearer to null. The potential fall along the length l is the measure of the emf. E is proportional to l.

We can write,

E ∝ l

From (ii) and (iii) we can write –

E₁ / l₁ = E₂ /l₂ = k

or, E₁ / l₁ = E₂ / l₂

8. A cell with internal resistance 1 ohm and emf 5 volts balances on a potentiometer wire at a length of 1.25 meters. The driving cell has an emf of 50 volts. If a 1-ohm wire connects the balance point and the battery, then the balance point will shift.

(Assuming that balancing length is measured from the higher potential side of pot wire.)

• A. 1.25 meters towards the right
• B. 1.25 meters towards the left
• C. 2.5 meters towards the left
• D. None of the above

At first, the balanced length is 1.25 m. Let’s consider it as l₁.

Now a wire of 1-ohm resistance connects the balance point and the cell.

We know that E = k * l

Here, l = l₁ and E = 5v

k * l₁ = 5                – (i)

Now the current through resistance is = (5/2) A = 2.5 A

By adding up the resistance of 1 ohm, the equivalent resistance comes as = 1+1 = 2 ohm.

Hence the E value for the later case becomes 2.5 v.

k * l₂ = 2.5             – (ii)

We know that –     

E₁/E₂ = l₂/l₁

from equations (i) and (ii), we find out –

5/2.5 = l₂/l₁

putting l₁ in the equation,

l₂ = 0.5 * l₁

     or, l₂ = 0.5 * 1.25

     or, l₂ = 0.625 m

So, the balance point shifts 0.625m towards the left.

The correct answer is the option – D. None of the above.

9. A potentiometer is better than a voltmeter for measuring emf of a cell. Why?

When we balance a cell against a pot wire, There is no current through the cell. The emf is measured then. Now, when we use a voltmeter to measure the emf for the cell, there is a small current which flows through the cell. Thus, we get only the terminal potential.

10. How can you increase the accuracy of the potentiometer?

The accuracy of a pot can be increased by maximizing the length of the wire up to a certain limit.

A circuit is a closed path that may contain several different electrical circuit elements, and a circuit can be series, parallel, or a combination of both series and parallel.

This article will discuss the series circuit function, definition, advantages, and disadvantages, etc.

Series Circuit Definition

A circuit can be a series, parallel, or combination of both series or parallel circuits. 

A series circuit combination is when every electric current element is connected from one terminal to another component’s terminal in such a way that there is only one way for the current to flow.

Series Circuit Function

There is the following essential function of a series circuit:

• In series, circuit current through each circuit element is identical regardless of the resistance or impedance of the components connected in the circuit.
• The voltage drop across each circuit element can vary with the value of resistance, impedance, or electrical characteristics of each circuit element.
• The total voltage drop in the overall series circuit is equal to the summation of the voltage drop across the individual component of the series circuit combination.
• When more than one resistor, capacitor, inductor, or voltage source are linked in a series combination that can be replaced by one equivalent value of resistor, inductor, capacitor or voltage source, respectively.
• The total power dissipated in the series circuit combination is amounting to the summation of individual power dissipated by each circuit element in the series circuit.
• The series circuit is also known as the voltage divider circuit. The potential drop across any circuit element is the function of the total voltage applied across the overall series circuit.

 Voltage in a Series Circuit

In a series circuit combination, the overall circuit voltage is split between the different series circuit elements.

If there is ‘n’ number of components is connected in a series circuit and V₁, V₂, V₃ …..V_n is the individual voltage across each element of the series circuit, then the total voltage (V) across the series circuit can be defined as:

V =V₁ + V₂+ V₃ …..+ V_n

The overall voltage in a series circuit is the summation of individual voltage across each electrical circuit element. The voltage across each electric component depends upon the electrical property of the respective element.

Current in a Series Circuit

The overall current of a series circuit has the same magnitude as the current across each circuit component.

If there is ‘n’ number of electrical components and I₁, I₂, I₃ … I_n, is the current through each component then the total current (I):

I = I₁ = I₂ = I₃ …= I_n 

The series circuit has a constant current magnitude in each part of the circuit; that is, the magnitude of the current is identical in every aspect of a series circuit.

 Series Circuit Working

There is only one path in which the electric current can flow through in a series circuit as all the electrical components in the series circuit are linked in a single path.

In a series circuit, the magnitude of the current is the same throughout the circuit. In contrast, the overall series circuit voltage gets divided between the several components of the circuit respectively.

In a series circuit, as the current passes through different components connected in a single path, each component has an identical current magnitude through it, which is also equal to the overall current in the circuit. In contrast, the voltage gets divided across each component in the series combination. A potential drop happens when the electrical potential energy gets converted into another form of energy by any electrical component. Hence, the potential drop depends on the energy conversion property of each element.

 Series Circuit Configuration

Any series circuit can be a combination of essential elements such as diode, capacitor, resistor, inductor, etc.

Let’s take a circuit of series configuration as given below

There is a series combination of one resistor, one inductor, a capacitor, and one diode is connected in a series combination with a voltage source in the above circuit.

Series Circuit Formula

the series circuit combination of more than one resistor, capacitor, and the inductor can be replaced by one equivalent value of the resistor, capacitor, inductor, respectively.

For Series Resistance

To calculate the total for overall resistance in a series circuit combination of n number of resistors, use the formula:

R_e = R₁+ R₂ + R₃ ……+R_n

Where R_e is the equivalent or total resistance of the series combination and R₁, R₂, R₃ … R_n are the resistance of individual resistors connected in series circuit combination of ‘n’ numbers of resistors.

For Series Capacitors

To calculate the total or overall capacitance of a series circuit combination consists of n number of capacitor use of formula:

where C_e is the equivalent of the total capacitance of the series circuit combination and C₁, C₂, C₃ … C_n  are the capacitance of individual capacitors connected in a series circuit combination of ‘n’ number of capacitor.

For Series Inductor

Use this formula to calculate the total or overall inductance of a series circuit combination consisting of n number of inductors:

L_e = L₁ + L₂+ L₃ …..+ L_n

Where Le is the equivalent of the total inductance of the series circuit combination and L₁, L₂, L₃ … L_n are the inductance of individual inductors connected in the series circuit.

Series Circuit Advantages 

Different advantages of the series circuit over parallel circuit are as follows:

• In a series circuit, each circuit element has the identical current magnitude passing through it.
• Voltage sources of any magnitude can be linked together in a series combination.
• Overall voltage can be increased in series circuit easily.
• In this series circuit, switching on or off of all the appliances together or devices can be done with only one switch.
• Series circuit combination does not get overheated easily.
• Series circuit has a straightforward design.

Series Circuit Disadvantages

As advantages of the series circuit discussed above, let’s now discuss the drawbacks of any series circuit as follows:

• Any fault or break in any component in the series circuit will affect the overall circuit.
• Faulty components or parts cannot be identified  easily as they are connected in series with each other.
• The current sources with different magnitudes cannot be connected in series with each other.
• All components connected in series have a single switch to turn on or turn off; they cannot be operated separately.
• The voltage drop(or potential drop) across each series circuit component may different from each other.

FAQ:

What is the purpose of a Series Circuit?

A series circuit can combine different circuit elements in a single path or branch of the circuitry.

A series circuit can be used where only one path is required between two points. The current through any series circuit is controlled as the magnitude of current remains the same throughout.

Is Current the same in Series?

Series circuit is known as voltage divider circuit as the voltage gets splited into all of its circuit components.

As there is only one path for the electric current to flow through, so the magnitude of the current remains the same throughout the circuit.

What is the Series Circuit in Electricity?

Series circuit is a type of closed path circuit, which can be a combination of several different electric components.

The series circuit can be defined as when the terminal of one circuit element is connected to the other terminal of the following circuit element in such a way that there is only one path for current to flow through.