What is Voltmeter?
In physics, there are different types of measuring equipment for electrical purposes. For measuring electrical current, voltage, and other parameters, the instruments are different. A voltmeter is one of the measurement equipment for electrical parameters. The voltmeter is used to measure the electrical potential difference between two points of an electrical circuit. To measure the potential difference, the voltmeter is connected in parallel with the electrical circuit. The voltmeter takes a small amount of current to form the power source to function. The amount of that current is too less and it doesn't affect the circuit current. In this article, we are discussing voltmeter definition, function, unit, and other information.
Voltmeter Function
The voltmeter is a vital instrument used to measure voltage. It is used to measure both direct and alternating electric current. A voltmeter is a current-controlled device, which means it needs a current to function. The voltmeter is connected with the electrical circuit in parallel. A voltmeter has high resistance so that it consumes less current to function. That is why the Current consumption by the voltmeter doesn’t affect the circuit current. In the parallel connection, the high resistance of the voltmeter gives almost the same impedance as the impedance of the load resistance. The voltage in the parallel circuit and the voltage between the voltmeter and the load become the same. Thus, the voltmeter measures the voltage of the electrical circuit. This is the working principle of a voltmeter.
Unit of Voltmeter
The voltmeter is the major instrument to measure the voltage of an electrical circuit. Therefore, the unit of the voltmeter is the unit of the voltage measured in the voltmeter. The units of voltmeter are millivolt, kilovolt and volt. These three are the most used units. 1 volt = 0.001 millivolts and 1 volt = 1,000 Kilovolts.
Classification of Voltmeter
Now, we are going to discuss different types of voltmeters. Voltmeters are classified depending on three factors, which are output, construction, and measurement. Voltmeters are of two types based on output - analog and digital voltmeters. Analog voltmeters display voltage with moving needles. Digital voltmeters show the voltage in a digital display with an accurate value.
Voltmeters are of five types based on construction - rectifier type voltmeter, MI voltmeter, electrodynamic voltmeter, PMMC, induction type voltmeter. Rectifier type voltmeter measures the voltage using a permanent magnet moving coil and rectifying elements. Moving iron (MI) voltmeter measures the voltage using the magnetic field created by moving iron. The electrodynamic voltmeter is constructed with a series connection of the windings, which gives the most accurate voltage values. PMMC voltmeters are constructed using permanent magnets. Induction type voltmeter Functions on the two-pole method or shaded pole method.
The voltmeters are classified into two types depending on the measurement, which are DC voltmeter and AC voltmeter. A DC voltmeter is used to measure the voltage of a DC power source. AC voltmeter is used to measure the voltage of an AC power source. These are the different types of voltmeters to measure the voltage of an electrical circuit.
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How to Measure Voltage Using a Voltmeter?
To measure the voltage of an electrical circuit, some particular steps should be followed. The essential steps are mentioned below.
Turn on the dial of the power source. If the circuit voltage is unknown, set the range to the highest value and set the dial on the source voltage.
Insert the black wire into the COM jack and the red wire into the voltage jack.
Remove the lead in reverse order, which means first red and then black.
Connect the test leads (first black and then red) to the circuit.
Read the voltage in the display. Remove the test leads in reverse order.
All the steps should be completed carefully. Otherwise, the measurement can be wrong or you can be injured.
Solved Examples
1. What is the Main Function of the Voltmeter?
Solution: Voltmeter is converted from a galvanometer. The main function of a voltmeter is to measure the voltage of an electrical circuit.
2. What is the Unit of a Voltmeter?
Solution: the main units of the voltmeter are volt, millivolt, and kilovolt.
3. Why is the Voltmeter Connected in Parallel?
Solution: Voltmeter has high resistance and it consumes less current to function. The current consumed by the voltmeter doesn’t affect the circuit. That is why the voltmeter is connected in parallel with the circuit.
4. What is the Main Difference Between DC and AC Voltmeters?
Solution: DC voltmeter is to measure DC voltage. AC voltmeter measures AC voltage.
FAQs on Voltmeter
1. What is a voltmeter and how does it function in a physics experiment?
A voltmeter is an instrument used to measure the electric potential difference (voltage) between two points in an electrical circuit. It functions by connecting in parallel to the portion of the circuit where voltage is measured, ensuring minimal disturbance to the circuit due to its high resistance design.
2. Which unit does a voltmeter use to display readings, and what do its prefixes mean?
The standard unit for voltage measured by a voltmeter is the volt (V). Common prefixes include millivolt (mV) for one-thousandth of a volt and kilovolt (kV) for one thousand volts, aligning with SI units used in physics.
3. Why must a voltmeter be connected in parallel in an electric circuit?
A voltmeter is always connected in parallel to the component whose voltage is to be measured. This ensures it measures the true potential difference across the component without significantly changing the current, as its high resistance draws minimal current.
4. What is the main difference between a DC voltmeter and an AC voltmeter?
A DC voltmeter measures potential difference in direct current (DC) circuits, while an AC voltmeter is designed for alternating current (AC) circuits. Internal circuit adaptations allow the instrument to handle the unique characteristics of each current type.
5. What are the types of voltmeters according to their output and construction?
Based on output, voltmeters are classified as analog (needle display) and digital (numeric display). In construction, they include:
- Rectifier type voltmeter
- Moving iron (MI) voltmeter
- Electrodynamic voltmeter
- Permanent magnet moving coil (PMMC)
- Induction type voltmeter
6. How does the high resistance of a voltmeter benefit its operation in circuits?
The high resistance present in a voltmeter minimizes the amount of current drawn from the circuit. This ensures the circuit's original current remains unchanged, allowing for accurate measurement of potential difference without affecting circuit performance.
7. If a voltmeter is accidentally connected in series, what would happen and why?
If a voltmeter is connected in series instead of parallel, its high resistance would greatly reduce or even stop the circuit current. This would prevent correct functioning of the circuit and result in improper voltage readings.
8. Why is it important to select the correct range on a voltmeter before measurement in practical exams?
Selecting the proper voltage range prevents overloading the voltmeter and ensures accurate readings. If the range is set too low, the instrument may be damaged; if set too high, the reading may lack precision. Start with the highest range if the voltage is unknown.
9. Explain, with examples, real-life applications where a voltmeter is essential.
Voltmeters are crucial for checking domestic power outlets, troubleshooting automotive electrical systems, verifying battery voltages, and monitoring voltages in laboratory experiments—ensuring appliances work safely and systems operate correctly.
10. What is the schematic symbol for a voltmeter and how is it represented in circuit diagrams?
The schematic symbol for a voltmeter is a circle with the letter V inside, connected in parallel across circuit elements. This clear graphical representation is a standard notation in circuit diagrams according to CBSE/NCERT conventions.
11. How does improper use of a voltmeter lead to errors in physics lab experiments?
Common errors include connecting the voltmeter in series, using an incorrect range, or loose connections. Each can lead to inaccurate readings, potential damage to the instrument, or unsafe lab conditions. Proper method, as per CBSE practical guidelines, should always be followed.
12. Compare analog and digital voltmeters in terms of accuracy and usage.
Analog voltmeters use a needle to display values and are more sensitive to parallax errors, whereas digital voltmeters offer precise numeric displays and are less prone to human reading errors, making them ideal for modern physics practicals.
13. In competitive exams, what conceptual traps occur when distinguishing between a voltmeter and an ammeter?
The main trap is confusing connection methods: voltmeters must be in parallel (measure voltage), while ammeters are in series (measure current). Incorrect connections lead to device malfunction or reading errors, a common practical and theory misconception.
14. How can the principles of voltmeter operation help in understanding electrical safety at home?
Understanding that a voltmeter measures potential difference without altering currents teaches the importance of correct wiring, insulation, and device specifications—key aspects for safely operating electrical appliances in household circuits as taught in CBSE/NCERT Physics.
