What is a voltmeter?

Short Answer

A voltmeter is an electrical instrument used to measure the potential difference or voltage between two points in a circuit. It shows the voltage in volts (V). To measure voltage correctly, a voltmeter is always connected in parallel with the component across which the voltage is to be measured.

A good voltmeter has very high resistance so that it does not draw extra current from the circuit. Voltmeters are commonly used in laboratories, homes, and industries to check the voltage of batteries, power supplies, and electrical devices.

Detailed Explanation

Voltmeter

A voltmeter is one of the most important measuring instruments used in electricity and electronics. It is designed to measure the electric potential difference, commonly known as voltage, between two points in a circuit. Voltage tells us how much electrical energy is available to push charges through a conductor. Without knowing voltage, it is difficult to understand the behavior of circuits or the performance of electrical devices.

A voltmeter displays its reading either on a scale with a pointer (analog voltmeter) or on a digital screen (digital voltmeter). The value shown is always in volts (V), which is the SI unit of potential difference.

Connection of a voltmeter

One of the most important rules for using a voltmeter is:

A voltmeter must always be connected in parallel with the component.

This parallel connection ensures that the voltmeter measures the exact potential difference across the device. If it were connected in series, it would block the current flow because voltmeters have very high resistance. Connecting it that way could damage the instrument as well as the circuit.

When connected in parallel, both the voltmeter and the component share the same two points, which is necessary for measuring voltage.

Resistance of a voltmeter

A good voltmeter has very high resistance. The purpose of high resistance is to reduce the current flowing through the voltmeter. If the voltmeter had low resistance, a large amount of current would pass through it, disturbing the circuit and giving incorrect readings.

High resistance ensures:

  • The voltmeter draws negligible current
  • The circuit’s actual behavior remains unchanged
  • The reading of voltage stays accurate

This is why voltmeters are designed differently from ammeters, which have very low resistance.

Working principle of a voltmeter

The basic working of a voltmeter is based on the moving coil mechanism for analog meters. When voltage is applied across the terminals of the voltmeter, a small current flows through its internal resistance and coil. This creates a magnetic field, which interacts with the permanent magnet, causing the coil and pointer to move. The pointer then shows the voltage value on the scale.

Digital voltmeters use electronic circuits, sensors, and microprocessors to measure voltage more accurately and display the value on a digital screen.

Types of voltmeters

While the question only asks what a voltmeter is, knowing the types helps understand the concept better:

  1. Analog voltmeter – Uses a pointer and scale to show voltage.
  2. Digital voltmeter – Displays voltage numerically on a screen.
  3. DC voltmeter – Measures voltage in direct current circuits.
  4. AC voltmeter – Measures voltage in alternating current circuits.

Digital voltmeters are more common today due to their accuracy and ease of reading.

Uses and applications of voltmeters

Voltmeters are used in many areas of daily life and industry, including:

  • Checking the voltage of batteries
  • Measuring voltage across bulbs, resistors, and other components in experiments
  • Testing electrical appliances
  • Monitoring power supply and distribution systems
  • Troubleshooting faults in circuits
  • Measuring AC voltage in homes and industries

Without voltmeters, it would be very difficult to work safely with electrical systems.

Features of an ideal voltmeter

An ideal voltmeter should have:

  • Infinite resistance (practically very high)
  • High accuracy and reliability
  • Quick response
  • Easy-to-read scale or display
  • Ability to measure over a wide voltage range

Although perfect voltmeters do not exist, modern instruments are designed to come very close to ideal behavior.

Difference between ammeter and voltmeter

A brief understanding helps:

  • Ammeter measures current and has low resistance; connected in series.
  • Voltmeter measures voltage and has high resistance; connected in parallel.

Both instruments together help understand the complete behavior of a circuit.

Conclusion

A voltmeter is an electrical measuring device used to measure the potential difference between two points of a circuit. It must be connected in parallel and has very high resistance to ensure accurate measurement. Voltmeters are essential tools in laboratories, homes, and industries for checking voltage levels, ensuring safety, and analyzing circuit performance. Whether analog or digital, a voltmeter plays a key role in understanding and working with electricity.