An electric charge e moves with a constant speed v parallel to the lines of force of a uniform magnetic field , B the force experienced by the charge is

Options

A. `(ev)/(B)`
B. `(e)/(B v)`
C. e Bv
D. zero

Answer

To solve the problem, we need to analyze the situation where an electric charge \( e \) is moving with a constant speed \( v \) parallel to the lines of force of a uniform magnetic field \( B \).

### Step-by-Step Solution:

1. **Understanding the Situation**:
- We have a charge \( e \) moving with speed \( v \).
- The magnetic field \( B \) is uniform and the charge is moving parallel to the field lines.

2. **Magnetic Force Formula**:
- The magnetic force \( F \) experienced by a charge moving in a magnetic field is given by the formula:
\[ F = q(\mathbf{v} \times \mathbf{B}) \]
- Here, \( q \) is the charge, \( \mathbf{v} \) is the velocity vector, and \( \mathbf{B} \) is the magnetic field vector.

3. **Identifying the Angle**:
- The angle \( \theta \) between the velocity vector \( \mathbf{v} \) and the magnetic field vector \( \mathbf{B} \) is crucial in determining the force.
- Since the charge is moving parallel to the magnetic field lines, the angle \( \theta \) is \( 0^\circ \).

4. **Calculating the Cross Product**:
- The sine of the angle \( \theta \) is used in the cross product:
\[ F = e v B \sin(\theta) \]
- Substituting \( \theta = 0^\circ \):
\[ F = e v B \sin(0^\circ) \]

5. **Evaluating the Sine Function**:
- We know that \( \sin(0^\circ) = 0 \).
- Therefore:
\[ F = e v B \cdot 0 = 0 \]

6. **Conclusion**:
- The magnetic force experienced by the charge \( e \) moving parallel to the magnetic field \( B \) is:
\[ F = 0 \]

### Final Answer:
The force experienced by the charge is **zero**.