1. Key Areas covered A moving charge produces a magnetic field
The determination of the direction of the force on a charged particle moving in a magnetic field for negative and positive charges (right-hand rule for negative charges).
Basic operation of particle accelerators in terms of acceleration, deflection and collision of charged particles.

2. What we will do today:
Describe how the force on an electric charge behaves when fired into an electric field at right angles.
Describe the direction of magnetic fields on both positively and negatively charged particles
Describe the basic operation of particle accelerators in terms of acceleration, deflection and collision of charged particles.

3. Deflection of Charged Particles

4. When a charge is placed in an electric field it experience a force*
*similar to a mass experiencing a force in a gravitational field
When an electric field is applied to a conductor (with free moving electrons), the free electric charges in the conductor move i.e. current flows
Work is done to moving the charge within the field

5. Revised Higher 2013 E

6. CfE Specimen Paper E

7. Interaction between electricity and magnetism
The discovery of the interaction between electricity and magnetism, and the resultant ability to produce movement, has to rank as one of the most important developments in physics in terms of the impact on everyday lives.
When a charged particle moves a magnetic field is generated. A current carrying wire will have a magnetic field around it.

8. How can we show this?
A magnetic field exists around a current-carrying conductor. This can be shown using compasses on a board, thick wire and a d.c. supply.

9. When the switch is open (no current) all the compasses point North.

10. What happens when the switch is closed?
The needles on the compass move in a circular direction.
This shows the direction of the magnetic field.

11. What happens when we change the direction of electron flow?
When we reverse the direction of the supply, the magnetic field also reverses in direction.

12. How can we tell the direction of the magnetic field?
It is possible to remember the direction of the magnetic field round a current-carrying wire for electron flow using the left-hand grip rule.
The thumb represents the direction of electron flow.
The (hands to the) fingers represent the magnetic field direction.

13. What will happen when a moving electric charge is brought into a static magnetic field?
The moving electric charge is surrounded by an (electro) magnetic field.
This interacts with the static magnetic field which causes the charge to experience a force.
Simple rules can be used to determine the direction of force on a charged particle in a magnetic field.

14. What happens to electrons (-ve charges)?
We use the right-hand motor rule.
The current, field and motion of force are all perpendicular to one another.
Current – Central finger
Field – Fore finger
Motion of force - ThuMb

15. What happens to protons (+ve charges)?
We use the left-hand motor rule.
(Same representation as previous)

16. Revised 2014 E

17. Revised 2013

18. Revised 2013

19. Do we have evidence of this?
The Sun produces a solar wind (a flow of charged particles) which can cause significant damage to life and electrical equipment.
The power of the solar wind can fluctuate over time.
Fortunately for us, Earth has a strong magnetic field (North and South poles) that interact with these charged particles.
The force produced by the magnetic field on the particles deflect them to the poles.
This is why Aurora (Northern and Southern lights) are produced.

20. Northern Lights links
BBC Nature - The greatest light show on Earth - info and video on Northern lights
The Northern Lights - Wonders of the Solar System - BBC - YouTube

21. How do we use this in practice? Particle Accelerators
The movement of charged particles in an electric field is a key component in particle accelerators.
Accelerators were invented to provide energetic particles to investigate the structure of the atomic nucleus.
Since then, they have been used to investigate many aspects of particle physics.
Particle accelerators speed up and increase the energy of a beam of particles by:
generating electric fields that accelerate the particles
magnetic fields that deflect (steer and focus) them.
A.C. is used to help change the direction of the force and in turn can change the direction of the acceleration.

22. Revised 2014 Qu 26

23. Past Paper Questions

24. Revised 2013 (1/2)

25. Revised 2013 (2/2)

27. Revised 2012 Qu: 26

28. Revised 2012 Qu: 26

29. Revised specimen paper (1/2)

30. Revised specimen paper (2/2)

32. Revised specimen paper

33. Possible answer The field is magnetic
When charged particles interact with a magnetic field they experience a force.
The direction of force is perpendicular to the flow of charges.
The direction can either be up or down depending on the charge.
As the solar wind is made up of both positive and negative charges this means there will be forces going both up and down.
This is why we have ‘Aurora’ in both the South and North Poles.