The correct answer is (b), telephone.
A carbon microphone is a type of microphone that uses a carbon element to convert sound waves into electrical signals. It is most commonly used in telephones, but it can also be used in other applications such as hearing aids and public address systems.
A carbon microphone works by applying pressure to a carbon element. This pressure causes the carbon granules to move closer together, which increases the resistance of the element. The electrical signal produced by the microphone is proportional to the amount of pressure applied to the carbon element.
The carbon microphone was invented in 1876 by Thomas Edison. It was the first practical microphone and it played a major role in the development of the telephone.
(a) A dynamo is a machine that converts mechanical energy into electrical energy. It is used to generate electricity in power plants.
(c) A transformer is a device that transfers electrical energy from one circuit to another. It does this by using electromagnetic induction to create a magnetic field that induces a voltage in the secondary circuit.
(d) None of these is the correct answer.