A: The work done by magnetic field on a moving charge is zero.
R: The magnetic force acting on a moving charge has no component in the direction of velocity.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark 2.
C. If assertion is true statement but Reason is false, then mark (3)
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To solve the assertion and reason question, we will analyze both statements step by step.

### Step 1: Understanding the Assertion
The assertion states that "the work done by a magnetic field on a moving charge is zero."

**Explanation**:
- Work done (W) is defined as the dot product of force (F) and displacement (S):
\[ W = \mathbf{F} \cdot \mathbf{S} \]
- If the force is perpendicular to the displacement, the work done is zero because the cosine of 90 degrees is zero.

### Step 2: Understanding the Reason
The reason states that "the magnetic force acting on a moving charge has no component in the direction of velocity."

**Explanation**:
- The magnetic force (\( \mathbf{F} \)) on a moving charge is given by:
\[ \mathbf{F} = q(\mathbf{v} \times \mathbf{B}) \]
where \( q \) is the charge, \( \mathbf{v} \) is the velocity, and \( \mathbf{B} \) is the magnetic field.
- The cross product indicates that the magnetic force is always perpendicular to both the velocity and the magnetic field. Therefore, it has no component in the direction of the velocity.

### Step 3: Conclusion
Since the magnetic force is perpendicular to the velocity of the charge, the work done by the magnetic field on the moving charge is indeed zero. Therefore, both the assertion and the reason are true, and the reason correctly explains the assertion.

### Final Answer
Both the assertion (A) and the reason (R) are true, and the reason correctly explains the assertion.

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