Question

Which of the following instruments is used to measure magnetic fields?
A) Thermometer
B) Pyrometer
C) Hygrometer
D) Flux meter

Answer 1

Hint: The measurement of magnetic fields is done using a coil that is present inside the measuring device. When the magnetic field interacts with the coil, it induces a voltage in the coil due to the changing flux experienced by the coil according to Faraday’s law of electromagnetic induction.

Complete answer:
Thermometers are used to measure temperatures of different bodies like we measure our body temperature when we have a fever. But they cannot measure magnetic fields
Pyrometer also is known as an Infrared thermometer/non-contact thermometer used to detect the temperature of an object’s surface temperature, which depends on the infrared/visible radiation emitted from the object. It has been widely used during the COVID-19 pandemic to measure the temperature of people in a non-contact manner. However, it cannot be used to measure the magnetic field.
A hygrometer is an instrument that is used to measure the amount of water vapour in the air, in soil or any kind of confined space. But it cannot be used to measure magnetic fields.
Flux meters use a coil which when interacts with a magnetic field produces an EMF due to the changing magnetic flux that is passing through the coil. Depending on the strength of the magnetic field, higher EMF will be induced and vice versa. So, we can measure the magnetic field using the flux meter.
Hence the correct answer is option (D).

Note:
Flux meters require a dynamic component for the measurement of the electric field. It is necessary for magnetic flux to cut the search coil to produce a voltage which is usually provided by changing the distance of the coil from the magnetic field, changing the number of turns of the coil or changing the area of the coils.