In a uniform magnetic field, the field lines are :

Options

A. curved
B. parallel and equidistant straight lines
C. parallel, but non-equispaced straight lines
D. nothing can be said.

Explanation

To solve the question regarding the characteristics of field lines in a uniform magnetic field, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Uniform Magnetic Field**:
- A uniform magnetic field is one where the magnetic field strength is the same in magnitude and direction at all points in the region.
- This means that the magnetic field lines will have specific characteristics.

2. **Identifying the Properties of Field Lines**:
- **Straight Lines**: In a uniform magnetic field, the field lines are straight. This indicates that the magnetic field does not vary in direction or strength.
- **Equidistant**: The distance between the magnetic field lines is constant. This means that the spacing between the lines is equal throughout the field.
- **Parallel**: The field lines are parallel to each other. This implies that they do not intersect or cross each other, indicating that the magnetic field is uniform.

3. **Evaluating the Options**:
- **Option A**: Curved lines - This is incorrect as uniform magnetic field lines are straight.
- **Option B**: Parallel, equidistant, and straight lines - This option correctly describes the properties of uniform magnetic field lines.
- **Option C**: Parallel but non-equidistant straight lines - This is incorrect since the lines must be equidistant in a uniform magnetic field.
- **Option D**: Nothing can be said - This is also incorrect as we can clearly define the properties of the field lines.

4. **Conclusion**:
- Based on the evaluation of the options, the correct answer is **Option B**: "Parallel, equidistant, and straight lines".

### Final Answer:
The correct answer is **Option B**: Parallel, equidistant, and straight lines.

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