If a charged particle enters a magnetic field, then it will:

Options

A. always experience a force by the magnetic field
B. never experiences any force
C. experience a force, if it is moving at right angles to the field
D. experience a force, if it is moving parallel to the field

Answer

To solve the question "If a charged particle enters a magnetic field, then it will:", we need to analyze the behavior of charged particles in a magnetic field based on their velocity relative to the magnetic field direction.

### Step-by-Step Solution:

1. **Understanding the Lorentz Force**:
The force experienced by a charged particle moving in a magnetic field is given by the Lorentz force equation:
\[ \mathbf{F} = q (\mathbf{v} \times \mathbf{B}) \]
where \( q \) is the charge of the particle, \( \mathbf{v} \) is the velocity vector of the particle, and \( \mathbf{B} \) is the magnetic field vector.

2. **Analyzing the Angle Between Velocity and Magnetic Field**:
The angle \( \theta \) between the velocity vector \( \mathbf{v} \) and the magnetic field vector \( \mathbf{B} \) plays a crucial role in determining the force:
- If \( \theta = 90^\circ \) (i.e., the particle enters perpendicular to the magnetic field), the sine of the angle is 1, and the force is maximized:
\[ F = qvB \sin(90^\circ) = qvB \]
- If \( \theta = 0^\circ \) (i.e., the particle moves parallel to the magnetic field), the sine of the angle is 0, and the force is zero:
\[ F = qvB \sin(0^\circ) = 0 \]
- If \( \theta = 180^\circ \) (i.e., the particle moves opposite to the magnetic field), the force is also zero:
\[ F = qvB \sin(180^\circ) = 0 \]

3. **Conclusion Based on the Angle**:
- A charged particle will **always experience a force** if it is moving perpendicular to the magnetic field.
- A charged particle will **never experience a force** if it is moving parallel or anti-parallel to the magnetic field.
- For angles between 0 and 90 degrees, the particle will experience a force that is less than the maximum force.

4. **Evaluating the Options**:
- **Option 1**: "Always experience a force by the magnetic field." - **Incorrect** (as it can be zero).
- **Option 2**: "Never experience any force." - **Incorrect** (as it can experience force when perpendicular).
- **Option 3**: "Experience a force if it is moving at right angles to the field." - **Correct**.
- **Option 4**: "Experience a force if it is moving parallel to the field." - **Incorrect** (as the force is zero).

### Final Answer:
The correct answer is **Option 3: Experience a force if it is moving at right angles to the field.**