Charged Particles

Overview

This lesson extends the motor-effect idea one more step. Instead of a wire carrying current, you now look at a moving beam of charged particles and work out how a magnetic field changes its direction.

What You Need to Know

• A moving charged particle is affected by a magnetic field.
• The force acts at right angles to both the magnetic field and the direction of motion.
• Because the force is sideways, the particle’s path changes direction rather than simply speeding up or slowing down.
• The same direction ideas used for a current-carrying conductor can be used to predict particle deflection.
• Reversing the magnetic field reverses the direction of the force.
• Reversing the direction of motion also reverses the deflection.

How to Work Through It

1. Start by revisiting the force on a current-carrying conductor so the link to earlier work is clear.
2. Replace the conductor with a moving beam of charge and identify the direction of motion on the diagram.
3. Practise deflection questions where either the field or the particle direction is reversed.
4. Finish by comparing several diagrams and justifying the direction of the force in each case.

Check Your Understanding

• Why does a charged particle need to be moving before a magnetic field can deflect it?
• In which direction does the magnetic force act compared with the field and the motion?
• What happens to the deflection if the magnetic field direction is reversed?

Common Mistakes

• Forgetting to identify the direction of motion before trying to apply the rule.
• Mixing up current direction with particle motion without checking the diagram carefully.
• Assuming the particle moves along the field line. The magnetic force acts sideways, not along the field.

Next Steps

• Use the lesson slides to practise several deflection diagrams until the pattern is secure.
• Bring together the whole topic before the next review lesson so the links between field, force, current, and induction stay clear.