Potentiometer vs Voltmeter: Working Principle, Accuracy, and Uses
Understanding the Difference Between Potentiometer And Voltmeter is crucial for students to analyze how instruments measure electric potential in circuits. This distinction is important for practical experiments and competitive exams like JEE, where precise knowledge of electrical measuring devices is frequently examined.
Understanding the Potentiometer in Electrical Circuits
A potentiometer is a device used to compare or measure the potential difference between two points in an electrical circuit with high accuracy. It uses a long, uniform wire and a sliding contact or jockey.
The potentiometer works by adjusting the sliding contact until no current flows through a galvanometer, indicating equal potential.
$V = k \cdot l$, where $k$ is potential gradient and $l$ is the null point length
Applications such as calibration and precise voltage measurements make potentiometers essential for laboratory work. For more on measuring electric quantities, refer to Difference Between Electric Potential in circuits.
Mathematical Meaning of Voltmeter
A voltmeter is an instrument designed to measure the voltage or potential difference between two points in a circuit directly. It typically has a high internal resistance to minimize circuit disturbance.
Voltmeters are attached in parallel across components and provide instant voltage readings, usually in volts, through an analog or digital display.
Modern voltmeters are widely used for monitoring or troubleshooting circuits. Their high impedance prevents them from affecting measurements, unlike devices with lower resistance. To understand more about different measuring techniques, see Difference Between Correlation And Covariance.
Comparative View of Potentiometer and Voltmeter
| Potentiometer | Voltmeter |
|---|---|
| Measures potential difference by comparison method | Measures potential difference directly |
| Based on null deflection (zero current) principle | Based on deflection principle (current flows) |
| Shows continuous range of values | Shows only discrete readings |
| Provides absolute potential measurement | Provides approximate potential difference |
| Does not draw current from the circuit under ideal conditions | Draws small current from the circuit |
| Can measure emf of cells accurately | Cannot measure emf without current drawn |
| Accuracy depends on wire length and uniformity | Accuracy depends on high resistance and calibration |
| No moving parts in simple forms | May have moving pointer (analog) or digital display |
| Used for calibration of other instruments | Used for routine voltage measurement |
| Not suitable for high-speed measurements | Provides fast voltage readings |
| Needs manual balancing | Provides automated readings |
| Long wire required for operation | Compact, easy to use in circuits |
| Sensitivity can be very high | Limited by internal resistance |
| Cannot be used directly in electrical power circuits | Used widely in power and electronic circuits |
| Used in laboratory and comparative experiments | Used in practical, field, and troubleshooting work |
| No scale is attached for reading | Calibrated scale or digital output present |
| Primarily measures small potential differences | Can measure large potential differences |
| Useful for calibration of standard cells | Not used for standard cell comparison |
| Low loading error during measurement | May introduce loading error due to current |
| Can be used to measure internal resistance of cells | Not suitable for internal resistance measurements |
Core Distinctions Between Potentiometer and Voltmeter
- Potentiometer uses comparison, voltmeter measures directly
- Potentiometer needs manual balancing; voltmeter is automatic
- Potentiometer ideal for sensitive measurements; voltmeter for speed
- Potentiometer causes no current flow; voltmeter draws some current
- Potentiometer not suitable for continuous measurements, voltmeter is
- Potentiometer mainly for calibration, voltmeter for quick checks
Worked Examples to Clarify Concepts
If a potentiometer wire of length 100 cm measures a null point at 40 cm when connected to a cell, the potential difference is proportional to that length.
Using a voltmeter, if a 6V battery is connected across its terminals, the voltmeter reads 6V immediately on the scale, showing direct measurement.
Where Potentiometer and Voltmeter Are Used
- Potentiometer calibrates standard cells and measures emf
- Voltmeter monitors voltage in electric circuits and devices
- Potentiometer used in precision laboratory experiments
- Voltmeter used in household appliances and troubleshooting
- Potentiometer determines internal resistance of cells
- Voltmeter checks battery output and circuit health
Summary in One Line
In simple words, potentiometer measures potential difference by comparison and without drawing current, whereas voltmeter measures potential difference directly but involves a small current in the circuit.
FAQs on Difference Between Potentiometer and Voltmeter
1. What is the main difference between a potentiometer and a voltmeter?
The primary difference between a potentiometer and a voltmeter is that a potentiometer measures potential difference more accurately by balancing the unknown voltage, while a voltmeter measures potential difference directly across two points.
Key points:
- Potentiometer uses the null deflection method for higher accuracy.
- Voltmeter draws some current and may affect circuit readings.
- Potentiometer is ideal for calibrating instruments; voltmeter is suitable for quick voltage checks.
2. Why is a potentiometer considered more accurate than a voltmeter?
A potentiometer is more accurate because it does not draw current from the circuit when measuring voltage, unlike a voltmeter.
Reasons:
- Utilizes the null method to achieve zero current flow during measurement.
- Eliminates loading effect caused by voltmeter resistance.
- Suitable for precise comparison and calibration of EMF and voltages.
3. What are the advantages of using a potentiometer over a voltmeter?
A potentiometer offers several advantages over a voltmeter for measuring potential difference.
Advantages:
- Provides highly accurate readings using the null method.
- Can compare and calibrate cells and other instruments.
- Does not draw current from the source under measurement.
- Minimizes errors due to internal resistance.
4. In what situations is a voltmeter preferred over a potentiometer?
A voltmeter is preferred when quick and direct voltage measurements are needed.
Situations:
- Daily laboratory use for rapid voltage checks.
- Field measurements where precision is less critical.
- When simplicity and speed are important.
5. Can a potentiometer measure both emf and potential difference?
Yes, a potentiometer can measure both emf and potential difference accurately by using the comparison method.
Measurement uses:
- Directly measures cell emf by balancing against standard voltage.
- Measures voltage drop across components in a circuit.
- Compares unknown EMF with a reference cell.
6. Why does a voltmeter give less accurate readings compared to a potentiometer?
A voltmeter is usually less accurate because it has a finite internal resistance and draws some current from the circuit.
Key reasons:
- The current drawn can alter the potential difference being measured.
- Loading effect reduces measurement precision.
- Best used where high accuracy is not required.
7. What is the working principle of a potentiometer?
A potentiometer operates on the principle of balancing a known voltage against an unknown one without drawing any current from the source under test.
Working principle:
- Voltage is balanced by adjusting the length of the wire until a null point is reached.
- No current flows at the null point, ensuring high accuracy.
- Used for accurate voltage and emf measurements.
8. What are the limitations of using a potentiometer?
Potentiometers have some limitations despite their high accuracy.
Limitations include:
- Not suitable for measuring rapidly changing voltages.
- Bulky and less portable compared to voltmeters.
- Measurement process is time-consuming.
- Requires a stable reference voltage for accuracy.
9. How does internal resistance affect the readings of a voltmeter and a potentiometer?
Internal resistance affects both instruments differently:
- Voltmeter: Lower internal resistance causes more current draw, impacting accuracy.
- Potentiometer: Since no current flows during measurement, internal resistance does not affect accuracy.
10. List two main differences between potentiometer and voltmeter.
The main two differences are:
- Potentiometer measures voltage using the null method and is highly accurate. Voltmeter measures voltage directly and is less accurate due to current draw.
- Potentiometer requires more setup time; voltmeter is quick and easy to use.
11. What is meant by the null method in potentiometer measurements?
The null method refers to a measurement technique where the circuit is adjusted until the galvanometer shows zero deflection, indicating no current flows through it.
This ensures highly accurate determination of unknown potential difference or EMF without drawing current from the circuit being measured.
12. How is standardisation of a potentiometer achieved?
Standardisation of a potentiometer is accomplished by adjusting it so that a known standard cell voltage balances a precise length of potentiometer wire.
Once standardised, it allows accurate comparison of unknown voltages and EMFs, as required in CBSE and other board practicals.
