When a charged particle enters a uniform magnetic field its kinetic energy

Options

A. Remains constant
B. Increases
C. Decreases
D. Becomes zero

Answer

**Step-by-Step Solution:**

1. **Understanding the Scenario**: When a charged particle, such as an electron, enters a uniform magnetic field, it experiences a magnetic force. This force acts perpendicular to the direction of the particle's velocity.

2. **Effect of Magnetic Force**: The magnetic force does not do work on the charged particle because it is always perpendicular to the velocity of the particle. Work is defined as the force applied in the direction of displacement, and since the magnetic force is perpendicular, it does not change the kinetic energy of the particle.

3. **Kinetic Energy Formula**: The kinetic energy (KE) of a particle is given by the formula:
\[ KE = \frac{1}{2} mv^2 \]
where \( m \) is the mass of the particle and \( v \) is its speed.

4. **Speed vs. Velocity**: While the direction of the particle's velocity changes due to the magnetic force, the magnitude (speed) of the velocity remains constant. Since the speed does not change, the kinetic energy also remains constant.

5. **Conclusion**: Therefore, when a charged particle enters a uniform magnetic field, its kinetic energy remains constant.

**Final Answer**: The kinetic energy of the charged particle remains constant when it enters a uniform magnetic field.

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