A: The magnetic field always accelerates a moving charge if the moving charge cuts the field lines.
R: When a moving charge cuts the magnetic field lines, the magnetic force on the charge is always non zero.

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 question, we need to analyze both the assertion (A) and the reason (R) provided:

**Assertion (A):** The magnetic field always accelerates a moving charge if the moving charge cuts the field lines.

**Reason (R):** When a moving charge cuts the magnetic field lines, the magnetic force on the charge is always non-zero.

### Step-by-Step Solution:

1. **Understanding the Assertion (A):**
- A magnetic field exerts a force on a moving charge. According to the Lorentz force law, the magnetic force (\(F\)) on a charge (\(q\)) moving with velocity (\(v\)) in a magnetic field (\(B\)) is given by:
\[ F = q(v \times B) \]
- If a charge is moving and cutting through magnetic field lines, it experiences a magnetic force that can change its direction of motion. However, this force does not change the magnitude of the velocity, only its direction.

2. **Analyzing the Motion of the Charge:**
- When a charged particle moves in a magnetic field, it typically undergoes circular motion due to the centripetal force provided by the magnetic force. This means that while the direction of the velocity changes, the speed (magnitude of velocity) can remain constant.
- Therefore, the statement that the magnetic field "always accelerates" the charge is misleading. Acceleration refers to a change in velocity, which can be due to a change in speed or direction. In this case, while the direction changes, the speed may not necessarily increase.

3. **Understanding the Reason (R):**
- The reason states that when a moving charge cuts the magnetic field lines, the magnetic force on the charge is always non-zero. This is true as long as the charge is moving at an angle to the magnetic field lines.
- The magnetic force is indeed non-zero when the charge is in motion and cutting through the magnetic field lines, confirming that there is a force acting on it.

4. **Conclusion:**
- Both statements A and R are true. However, the assertion (A) is not entirely accurate because it implies that the magnetic field always increases the speed of the charge, which is not the case. The reason (R) correctly explains that a force is acting on the charge, but it does not justify the assertion that the charge is always accelerated in terms of speed.

5. **Final Evaluation:**
- Since both A and R are true, but R does not correctly explain A, we conclude:
- A is true.
- R is true.
- R is not the correct explanation of A.

### Answer:
Both A and R are true, but R is not the correct explanation of A.