Potentiometer

Potentiometer: Definition, Principle, Construction and Uses

Definition

Potentiometer is an accurate device that is used to measure or compare the potentials without drawing any current from the circuit.

Principle

When steady current flows through the wire of uniform cross-section area then the potential difference across any length of wire is directly proportional to its length i.e.,

, when I = constant

Construction

A potentiometer consists of a resistor in form of a wire of length L on which a terminal c can slide. Let, R is the resistance of a wire. As the sliding contact moves from A to B, the resistance between A and C changes from O to R.

Potentiometer

Potentiometer as Potential divider

Let suppose E be the emf of the cell. The current flowing through it is

Potentiometer-eqation

If R be the resistance between A and C then the potential drop between these points will be

eqation-2

Putting the value of I from the equation, we get

eqation-3

As E and R are constant for a given circuit, therefore the potential drop can be varied by changing the value of r. This arrangement is known as a potential divider.

Measurement of emf

A potentiometer can be used for measuring the unknown emf of a cell. It consists of a resistance wire R of a uniform cross-sectional area. let say E x is the unknown emf of the cell. It should be kept in mind that the positive terminal of the cell and that of the potential divider are connected to the same point A.

When the terminal C and negative terminal of E x are at the same potential, then no current will flow through the galvanometer. Under this condition, the emf E x of the cell is equal to the potential difference between A and C i.e., eqation-4

In the case of a wire of uniform cross-sectional area, the resistance is directly proportional to length i.e.,   Now the equation will become

equation-5

Where l is the length of wire between A and C and L is the total length of wire.

Comparing emf of two cells

The method which is used to measure the emf of a cell can also be used to compare E1 and E2 of two cells. Let l1 and l2 are the balancing lengths for EMFs of two cells E1 and E2 respectively. Li and l2 are calculated separately for each cell.

Further Reading:  Bohr’s Model of Hydrogen Atom

equation-6

Dividing both:                      equation-7

The ratio of the EMFs is equal to the ratio of their balancing length.

Uses of Potentiometer

It can be used

  1. For determination of emf of the cell.
  2. For comparing EMFs of two cells.
  3. As a continuously potential divider.
  4. For measuring the internal resistance of the cell.

MCQs about Potentiometer

FAQs Related to Potentiometer Tutorial:

  1. What is a potentiometer?
    • A potentiometer is an accurate device used for measuring or comparing potentials without drawing any current from the circuit.
  2. What is the principle behind a potentiometer?
    • The principle involves the direct proportionality between the potential difference across a length of wire and its length when a steady current flows through it.
  3. How is a potentiometer constructed?
    • It consists of a resistor in the form of a wire with a sliding terminal (slider). As the slider moves along the wire, the resistance between two points changes.
  4. How is a potentiometer used as a potential divider?
    • By varying the position of the slider, the potential drop across a portion of the wire can be adjusted, effectively dividing the total potential difference.
  5. What is the purpose of using a potentiometer for measuring EMF?
    • A potentiometer can measure the unknown EMF of a cell by balancing its potential difference against a known reference voltage.
  6. How can a potentiometer compare the EMF of two cells?
    • The method used for measuring the EMF of a single cell can also be applied to compare the EMFs of two cells by observing the balancing lengths on the potentiometer wire.
  7. What are the practical uses of a potentiometer?
    • Potentiometers are used for determining the EMF of a cell, comparing EMFs of two cells, serving as a continuously variable potential divider, and measuring the internal resistance of a cell.
  8. Can a potentiometer draw current from the circuit during measurement?
    • No, a potentiometer does not draw any current from the circuit during measurement, ensuring accurate potential readings.
  9. What factors influence the accuracy of measurements with a potentiometer?
    • Factors such as the uniformity of the wire’s cross-sectional area and the precision of the slider’s movement can affect the accuracy of measurements with a potentiometer.
    1. How does a potentiometer measure EMF without drawing current from the circuit?
    • A potentiometer balances the potential difference produced by the EMF of a cell against a known reference voltage, without allowing any current to flow through the circuit, ensuring accurate measurement.
    1. What is the significance of the sliding terminal (slider) in a potentiometer?
    • The sliding terminal allows for the adjustment of the position along the wire, effectively changing the portion of the wire over which the potential difference is measured.
    1. What role does the uniform cross-sectional area of the wire play in potentiometer measurements?
    • The uniform cross-sectional area ensures uniform resistance along the length of the wire, enabling accurate measurements of potential differences.
    1. Why is it important to connect the positive terminal of the cell to the same point as the potential divider in EMF measurements?
    • Connecting the positive terminal of the cell and the potential divider to the same point ensures that their potentials are equal, facilitating accurate balancing and measurement.
    1. Can a potentiometer be used to measure the internal resistance of a cell?
    • Yes, a potentiometer can measure the internal resistance of a cell by comparing its EMF with and without an external load, allowing for the calculation of the internal resistance.
    1. How does a potentiometer help in comparing the EMFs of two cells?
    • By measuring the balancing lengths of the potentiometer wire for each cell separately, the EMFs of the two cells can be compared directly using the ratio of their balancing lengths.
Further Reading:  Geiger Muller Counter [Principle, Working, & Uses]

Summary:

Understanding Potentiometers: A Comprehensive Overview

Potentiometers, also known as pots, are indispensable tools in electrical measurements due to their precision and versatility. This summary provides an insightful glimpse into their definition, principle of operation, construction details, and practical applications.

Definition and Principle: Unveiling the Core Concepts

At its essence, a potentiometer serves as an accurate device for gauging or comparing electrical potentials without disrupting the circuit by drawing current. This functionality stems from the fundamental principle that the potential difference across a segment of wire is directly proportional to its length when a constant current flows through it.

Construction: Delving into the Inner Workings

A potentiometer typically comprises a resistor wire of uniform cross-section, upon which a sliding terminal can traverse. This arrangement enables the adjustment of resistance between designated points, facilitating precise control over potential drop, thus earning its designation as a potential divider.

Potentiometer as a Potential Divider: Unlocking its Functionalities

By harnessing its potential divider configuration, a potentiometer empowers engineers and scientists to manipulate potential drop within a circuit. This flexibility proves invaluable in various applications, such as measuring EMFs of cells and comparing EMFs of different cells through balancing lengths.

Practical Applications: Unleashing Potentiometer’s Versatility

The utility of potentiometers extends across a spectrum of tasks, including determining cell EMFs, comparing EMFs of diverse cells, and even assessing internal cell resistance. Its continuous potential divider functionality further broadens its scope in electrical measurements.

Further Reading:  An intro about Ohm’S LAW

Conclusion: Embracing the Power of Potentiometers

In conclusion, potentiometers emerge as indispensable tools in the realm of electrical engineering, offering precise measurements and versatile functionalities. Their ability to accurately gauge and manipulate electrical potentials without disrupting circuits underscores their significance in various applications. Whether in laboratories, workshops, or industrial settings, potentiometers remain steadfast allies for engineers and scientists alike.