2. Magnetic Fields
Bar Magnet N S

3. Bar Magnets Field acts as a North Pole would move,
i.e. From North to South.
Vyrfd
Field lines are complete circles.

4. Earth’s Magnetic Field
The magnetic north pole is in the southern hemisphere
Denu

5. Our magnetic field is changing

6. History of Earth’s Fields

7. South Atlantic Anomaly

8. South Atlantic Anomaly

12. Magnet Field and Current
(Conventional
Current)
Right Hand Grip Rule
Fefd

14. Flemings Left Hand Rule

15. F = B Il Bil. Length of conductor in field. Force
Magnetic Field Strength
Current
Also known as Magnetic Flux Density.

16. WHICH WAY WILL IT GO? N S

17. WHICH WAY WILL IT GO? S N

18. WHICH WAY WILL IT GO? N S

19. WHICH WAY WILL IT GO? S N

20. WHICH WAY WILL IT GO? S N

21. WHICH WAY WILL IT GO? S N

22. WHICH WAY WILL IT GO? N S

23. WHICH WAY WILL IT GO? N S

24. WHICH WAY WILL IT GO? S N

25. WHICH WAY WILL IT GO?
N S

26. WHICH WAY WILL IT GO?
N S

27. WHICH WAY WILL IT GO?
S N

28. Mass Spectrometer

29. Magnetic Flux The magnetic flux density (B) x the area swept out (A)
= magnetic flux (theta)
Units Webber
Dt bring

30. Electromagnetic Induction
A moving charge in a magnetic field experiences a force (to make it move).
Therefore moving a conductor in a field will cause a current to flow.
This is electromagnetic induction.
Or a varying magnetic field over a conductor will also cause a current.

31. Electromagnetic Induction
Flux cutting.
The conductor has to cut field lines for an emf to be induced.
Discussion: How is the ‘electricity’ made?
The demonstrations have shown that ‘making’ electricity involves magnetic fields, but what is really going on? Your students already know that charges moving across a magnetic field experience a force (the BIL force). Now, the metal of a conductor contains mobile charges, the conduction electrons. What happens to these if the conductor is moved across a magnetic field?
Consider a conducting rod PQ moving at a steady speed v perpendicular to a field with a flux density B. An electron (negative charge e) in the rod will experience a force (= Bev) (Fleming's left hand rule) that will push it towards the end Q. The same is true for other electrons in the rod, so the end Q will become negatively charged, leaving P with a positive charge. As a result, an electric field E builds up until the force on electrons in the rod due to this electric field (= Ee) balances the force due to the magnetic field.
Ee = Bev so E =Bv
For a rod of length L, E = V/L and so V/L = Bv
Hence the induced EMF E = BLv
Clearly what we have here is an induced EMF (no complete circuit so no current flows) and already we can see that more rapid movement gives a greater induced EMF.
Now consider what happens when the EMF drives a current in an external circuit. To do this, imagine that the rod moves along a pair of parallel conductors that are connected to an external circuit.

32. Magnetic Flux Linkage Through a coil of N turns n theta = n BA
N theta = NBAcos theta
when the magnetic field is along the normal (perpendicular) of the coil face the N theapta = NBA
When the coil is turned 180 then N theta = -NBA
When the magnetic field is parallel to the coil flux linkage = 0

33. Faraday's Law
The induced emf in a conductor is equal to the rate of change of flux linkage through the circuit.
Write this out as an equation.
Derive the equation from V= W/Q