A magnetic field cannot exert any force on a

Options

A. moving magnet
B. moving charge
C. stationary magnet
D. stationary charge

Explanation

### Step-by-Step Solution:

1. **Understanding the Concept**: A magnetic field exerts a force on charged particles that are in motion. The force experienced by a charged particle in a magnetic field is given by the equation:
\[ \vec{F} = Q (\vec{V} \times \vec{B}) \]
where \( \vec{F} \) is the magnetic force, \( Q \) is the charge, \( \vec{V} \) is the velocity of the charge, and \( \vec{B} \) is the magnetic field.

2. **Analyzing the Situation**: For a magnetic field to exert a force, the charged particle must be moving. If the particle is stationary, its velocity \( \vec{V} \) is zero.

3. **Applying the Formula**: If we substitute \( \vec{V} = 0 \) into the force equation, we get:
\[ \vec{F} = Q (0 \times \vec{B}) = 0 \]
This shows that the force \( \vec{F} \) is zero when the charged particle is stationary.

4. **Conclusion**: Therefore, a magnetic field cannot exert any force on a stationary charge. The same reasoning applies to stationary magnets, as they do not have a velocity in the magnetic field.

5. **Final Answer**: A magnetic field cannot exert any force on a **stationary charge**.