What is a toroid ?

Options

A. Ring Shaped Solenoid
B. Charged particle.
C. Spherical coil
D. None of A and B

Explanation

### Step-by-Step Solution:

1. **Definition of a Toroid**: A toroid is a three-dimensional geometric shape that resembles a doughnut or a ring. It is formed by bending a solenoid into a circular shape.

2. **Structure of a Toroid**: A toroid consists of a coil of wire that is wound in a circular manner around a central axis. The wire is usually insulated to prevent short-circuiting.

3. **Magnetic Field in a Toroid**: When an electric current passes through the wire of the toroid, it generates a magnetic field. The magnetic field lines inside the toroid are concentrated and circular, resembling those of a solenoid, but they are confined within the toroidal shape.

4. **Comparison with Other Options**:
- A **ring-shaped solenoid** is essentially the same as a toroid, as it describes the same structure.
- A **charged particle** does not describe a toroid.
- A **spherical coil** is different from a toroid, as it does not have the same ring-like structure.

5. **Conclusion**: Therefore, the correct answer to the question "What is a toroid?" is that it is a ring-shaped solenoid.