Electromagnets are used in

Options

A. electric bells only
B. telephones only
C. dynamos only
D. all the above

Answer

**Step-by-Step Solution:**

1. **Understanding Electromagnets:**
Electromagnets are magnets created by electric current. When current flows through a wire, it generates a magnetic field around it. This principle is utilized in various devices.

2. **Identifying Uses of Electromagnets:**
We need to identify the devices that utilize electromagnets. The options provided are:
- Electric bell
- Telephone
- Dynamo

3. **Electric Bell:**
In an electric bell, there is a hammer (or striker) that strikes a gong. The mechanism works as follows:
- When the bell is switched on, current flows through the electromagnet, creating a magnetic field.
- The electromagnet attracts the hammer towards itself, striking the gong.
- When the hammer strikes the gong, it breaks the circuit, stopping the current flow and the electromagnet turns off.
- The hammer then returns to its original position, allowing the circuit to close again, and the process repeats.

4. **Telephone:**
In a telephone, electromagnets are used to convert electrical signals into sound:
- The earpiece contains an electromagnet and a diaphragm.
- When current flows through the electromagnet, it attracts the diaphragm, causing it to vibrate.
- These vibrations produce sound waves that we can hear.

5. **Dynamo:**
A dynamo generates electricity using electromagnetic induction:
- It consists of an armature and a stator with magnets.
- When the armature rotates within the magnetic field created by the electromagnets, it induces an electric current.
- This principle is fundamental in converting mechanical energy into electrical energy.

6. **Conclusion:**
All three devices—electric bell, telephone, and dynamo—utilize electromagnets for their operation. Therefore, the answer is that electromagnets are used in all of the options provided.