Production of magnetic field can be done by:

Options

A. Changing electric field
B. Moving charge only
C. Both (a) and (b)
D. Changing polarity of the wire in electric field

Explanation

To solve the question regarding the production of a magnetic field, we can break down the concepts involved step by step.

### Step-by-Step Solution:

1. **Understanding Magnetic Fields**: A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials.

2. **Production by Moving Charges**: One fundamental way to produce a magnetic field is through moving electric charges. When charges move, they create a magnetic field around them. This is described by Ampère's law, which states that the magnetic field in space around an electric current is proportional to the electric current.

3. **Electric Current**: An electric current consists of a flow of electric charge, typically electrons in a conductor. When a current flows through a wire, it generates a magnetic field in the surrounding space.

4. **Right-Hand Rule**: The direction of the magnetic field produced by a current-carrying conductor can be determined using the right-hand rule. If you point the thumb of your right hand in the direction of the current, your fingers will curl in the direction of the magnetic field lines.

5. **Magnetic Field from Electric Fields**: Additionally, a changing electric field can also produce a magnetic field. This is a key principle in electromagnetism, described by Maxwell's equations. A time-varying electric field induces a magnetic field.

6. **Conclusion**: Therefore, the production of a magnetic field can be achieved by:
- Moving charges (electric current)
- Changing electric fields

### Final Answer:
The production of a magnetic field can be done by moving charges (electric current) and changing electric fields.

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