A moving coil voltmeter measures

Explanation:

Moving Coil Voltmeter

Definition: A moving coil voltmeter is an instrument used to measure the voltage (potential difference) in an electrical circuit. It operates on the principle that a current-carrying conductor placed in a magnetic field experiences a torque, causing the conductor to move. This movement is translated into a readable voltage measurement on a calibrated scale.

Working Principle: The moving coil voltmeter works based on the interaction between the magnetic field of a permanent magnet and the current passing through a rectangular coil. The coil is wound on a lightweight aluminum or copper frame and is suspended in the magnetic field of a permanent magnet. When a current flows through the coil, it experiences a torque due to the Lorentz force, causing it to rotate. This rotation is proportional to the voltage applied across the meter, and the pointer attached to the coil moves over a calibrated scale to indicate the voltage value.

Correct Option Analysis:

The correct option is:

Option 2: Only d.c. voltage

A moving coil voltmeter is designed to measure only direct current (d.c.) voltage. This is because the moving coil mechanism relies on the direction of current flow to generate a consistent torque. In the case of alternating current (a.c.), the current direction changes periodically, causing the torque to reverse as well. This results in the pointer oscillating around the zero mark rather than providing a stable reading. Therefore, a moving coil voltmeter is inherently suitable for measuring d.c. voltage only.

Advantages of Using a Moving Coil Voltmeter for D.C. Voltage:

• High sensitivity and accuracy due to the precision of the moving coil mechanism.
• Linear scale, making it easier to read and interpret the voltage measurement.
• Low power consumption as the instrument requires minimal current to operate.

Disadvantages:

• Cannot measure a.c. voltage without the addition of a rectifier circuit.
• Fragile components, such as the moving coil and suspension system, require careful handling.
• Limited range of voltage measurement, typically requiring external shunts or multipliers for higher voltages.

Applications:

• Used in laboratories and industries to measure d.c. voltage in electronic circuits.
• Common in battery testing and d.c. power supply measurements.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Only a.c. voltage

This option is incorrect. A moving coil voltmeter cannot measure a.c. voltage directly due to the alternating nature of the current, which causes the pointer to oscillate instead of providing a steady reading. However, with the addition of a rectifier circuit, the moving coil voltmeter can be adapted to measure a.c. voltage by converting it into d.c. voltage first. Without such modifications, the moving coil voltmeter is not suitable for a.c. voltage measurement.

Option 3: Both a.c. and d.c. voltage

This option is incorrect as well. While a moving coil voltmeter can measure d.c. voltage directly, it cannot measure a.c. voltage without additional components like a rectifier. Therefore, it is not capable of measuring both a.c. and d.c. voltage in its basic form.

Option 4: Nothing

This option is incorrect. A moving coil voltmeter is a precise and reliable instrument for measuring d.c. voltage. As explained earlier, it operates effectively within its designed scope, which is limited to d.c. voltage measurement.

Option 5:

The question provides no content for option 5, making it irrelevant to the analysis. It has no bearing on the discussion of the moving coil voltmeter's functionality.

Conclusion:

The moving coil voltmeter is a highly sensitive and accurate instrument designed specifically for measuring d.c. voltage. Its operation is based on the interaction between a magnetic field and current in a coil, which results in a proportional deflection of the pointer. While it cannot measure a.c. voltage directly due to the oscillatory nature of alternating current, it remains an indispensable tool for d.c. voltage measurements in various applications, such as laboratories and industries. The correct answer is option 2, as the instrument is inherently suited for measuring only d.c. voltage.