Assertion : Magnetic field do not work on moving charge
Reason : Magnetic field do not provide acceleration to charge.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Answer

To analyze the given assertion and reason, let's break down the concepts step by step.

### Step 1: Understanding the Assertion
**Assertion**: Magnetic fields do not work on moving charges.

- When a charged particle moves through a magnetic field, it experiences a magnetic force 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.

- The key point is that this force is always perpendicular to the velocity of the charge. Since work done is defined as:
\[ W = \vec{F} \cdot \vec{d} \]
where \( \vec{d} \) is the displacement, and since \( \vec{F} \) is perpendicular to \( \vec{v} \), the work done by the magnetic field is zero. Therefore, the assertion is **correct**.

### Step 2: Understanding the Reason
**Reason**: Magnetic fields do not provide acceleration to charges.

- While the magnetic field does not do work on the charge, it can still exert a force that changes the direction of the charge's velocity. This change in direction constitutes acceleration.

- Acceleration is defined as the rate of change of velocity. Even if the magnitude of the velocity remains constant, a change in direction means there is acceleration:
\[ \text{Acceleration} = \frac{\Delta \vec{v}}{\Delta t} \]

- Therefore, the reason is **incorrect** because the magnetic field does indeed provide acceleration to the charge by changing its direction.

### Conclusion
- The assertion is **true**: Magnetic fields do not work on moving charges.
- The reason is **false**: Magnetic fields do provide acceleration to charges by changing their direction.

### Final Answer
Assertion is true, but the reason is false.