Electromagnetic Wattmeter for Utility Frequency Measurement

Utility frequency, also known as power frequency, is the frequency of the oscillating voltage and current in an electric power grid. In most parts of the world, this is either 50 Hz or 60 Hz.

The question asks to identify the instrument used to measure these utility frequencies from the given options.

Understanding the Electromagnetic Wattmeter

An Electromagnetic Wattmeter is a type of wattmeter that measures the electric power in an AC circuit. Its operation is based on the interaction of magnetic fields produced by two coils:

• A current coil, connected in series with the load, carrying the load current.
• A potential coil, connected in parallel with the load, carrying current proportional to the voltage across the load.

The deflection of the meter's pointer is proportional to the average power consumed by the load, calculated as:

\( P = V \times I \times \cos(\phi) \)

where \( P \) is the power, \( V \) is the voltage, \( I \) is the current, and \( \cos(\phi) \) is the power factor.

Identifying the Instrument for Utility Frequency

Based on the options provided and the designated correct answer, the instrument used to measure utility frequencies is the Electromagnetic Wattmeter.

While an electromagnetic wattmeter's primary function is to measure power, in the context of this question, it is presented as the instrument for measuring utility frequencies.

Let's look at the other options:

• Multimeter: A versatile instrument that can measure various electrical properties like voltage, current, and resistance. Many modern digital multimeters also have a frequency measurement function.
• Energy meter: Measures the total amount of electrical energy consumed over a period, typically in kilowatt-hours (kWh).
• Techometer (Tachometer): An instrument used to measure the rotational speed of a shaft or disk, usually expressed in revolutions per minute (RPM).

Considering the provided information, the Electromagnetic Wattmeter is indicated as the correct instrument for measuring utility frequencies.