Question

A carbon microphone is best used in a
A. dynamo
B. telephone
C. transformer
D. none of these

Answer 1

Hint: A microphone is a transducer device that converts physical sound vibration signals into electrical signals. In any kind of microphone a diaphragm vibrates and according to those vibrations electrical signals are produced.

Complete step-by-step answer:
For this question it is important to know something about all the devices in the options.
The first option is dynamo. A dynamo is also called a generator of electricity. It has nothing to do with sound therefore, we can discard this option.
Next we consider transformers. A transformer is a device that converts high current low voltage AC into low current High Voltage AC. So, it basically deals with electrical signal transfers but also has nothing to do with sound.
Only Telephone is a device that requires external sound to be converted into electrical (digital) signals and transfer these signals to remote locations. Therefore, a carbon microphone must be used in a telephone. Therefore, the correct answer is option (B).

So, the correct answer is “Option B”.

Additional Information: Carbon microphone was invented in 1870's by David Edward Hughes. It was one of the earliest microphones to be used. It consists of carbon granules packed inside two metal plates. As sound is produced, these plates get compressed or relaxed accordingly. In a carbon microphone the resistance of the carbon molecules inside the plates decreases when they are compressed so as the potential difference is applied, the current in the circuit will increase upon compression.

Note: It is better to know that a microphone translates physical signals of sound vibrations into electrical signals. Such types of devices fall in the category of transducers. Transducers are basically devices that translate between a physical signal and an electrical signal where physical signals can also be in the form of pressure, temperature, etc.