Physics 2002 JAMB Past Questions - Question 42: The carbon-granule microphone works on the principle of change in

Correct Answer

C

Explanation

A carbon-granule microphone, also known as a carbon microphone or a carbon button microphone, works on the principle of a change in electrical resistance caused by the compression of carbon granules between two electrodes.

Here's how it works:

1. Carbon Granules: Inside the carbon microphone, there are tiny carbon granules that are loosely packed between two electrodes. The granules are typically made of carbon powder.

2. Diaphragm: The front of the microphone has a diaphragm, which is a thin, flexible membrane. Sound waves in the surrounding environment cause this diaphragm to vibrate.

3. Compression of Carbon Granules: When sound waves hit the diaphragm, it vibrates. As it vibrates, it exerts pressure on the carbon granules behind it. This pressure causes the granules to compress or vary in density.

4. Change in Electrical Resistance: The variation in the density of the carbon granules changes their electrical resistance. When the granules are more tightly packed due to compression, their electrical resistance decreases. Conversely, when the granules are less compressed, their resistance increases.

5. Electrical Circuit: The two electrodes, one in front of the carbon granules and one behind, are connected to an electrical circuit. As the carbon granules change their resistance, it affects the electrical current passing through the microphone.

6. Electrical Signal: The variations in electrical resistance result in an electrical signal that mimics the incoming sound waves. This signal can then be amplified and used for recording or transmitting audio.

Carbon microphones were one of the earliest types of microphones used in telephony and early broadcasting. They were simple but effective in converting sound into electrical signals. However, they have largely been replaced by more modern and higher-quality microphone technologies, such as condenser and dynamic microphones, for professional audio applications.