A proton is moved along a magnetic field line.The magnetic force on the particle is

Options

A. along its velocity
B. opposite to its velocity
C. perpendicular to its velocity
D. zero

Explanation

To solve the question regarding the magnetic force on a proton moving along a magnetic field line, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Situation**:
- A proton is moving along a magnetic field line. This means that the direction of the proton's velocity (v) is parallel to the direction of the magnetic field (B).

2. **Recall the Formula for Magnetic Force**:
- The magnetic force (F) on a charged particle is given by the equation:
\[ F = q(\mathbf{v} \times \mathbf{B}) \]
- Here, \( q \) is the charge of the particle, \( \mathbf{v} \) is the velocity vector, and \( \mathbf{B} \) is the magnetic field vector.

3. **Determine the Angle Between v and B**:
- Since the proton is moving along the magnetic field line, the angle \( \theta \) between the velocity vector \( \mathbf{v} \) and the magnetic field vector \( \mathbf{B} \) is 0 degrees.

4. **Apply the Sine Function**:
- The force can also be expressed as:
\[ F = qvB \sin(\theta) \]
- Since \( \theta = 0 \) degrees, we have:
\[ \sin(0) = 0 \]

5. **Calculate the Magnetic Force**:
- Substituting \( \sin(0) \) into the equation gives:
\[ F = qvB \cdot 0 = 0 \]
- Therefore, the magnetic force acting on the proton is 0.

6. **Conclusion**:
- Since the proton is moving parallel to the magnetic field, the magnetic force on the proton is zero.

### Final Answer:
The magnetic force on the proton is **0**.

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