Question

Which of the following is not a part of carbon microphone?

• A. AC source
• B. Step-up transformer
• C. Grid Diaphragm
• D. Chamber containing carbon particles

Hint:

Carbon microphones are famous for their high output and ruggedness, which is why they were used as the standard transmitters in telephone handsets for nearly a century. However, they suffer from a high background hiss caused by current flowing through the carbon granules.

Answer 1

The Correct Option is A

Step 1: Understanding Carbon Microphone Operation:
A carbon microphone operates on the principle of variable resistance. It consists of a cup containing fine carbon granules placed behind a flexible metal diaphragm.

Step 2: Identifying the Parts of the System:

• Chamber with Carbon Particles (D) and Diaphragm (C): When sound waves strike the diaphragm, it vibrates, compressing and releasing the carbon granules. This varies the contact resistance between the granules.
• DC Battery Source (Not AC): To convert this resistance variation into an electrical signal, a Direct Current (DC) source (battery) must be connected in series with the carbon chamber.
• Step-up Transformer (B): The fluctuating DC current is passed through the primary winding of a step-up transformer, which induces a higher AC audio voltage in its secondary winding for output.

Step 3: Conclusion:
Because a carbon microphone requires a DC supply to function and does not use an AC source, option (A) is the correct answer.