1. We know spinning electrons make a magnetic field…
…so do FLOWING electrons!
Hans Christian Oersted 1820 accidently discovered this link between magnetism and electricity.
DEMO – compass and current-carrying wire

2. Magnetic Field and Right Hand Rule

4. A loop of wire results in a stronger field inside loop…
Right hand rule still holds

5. A coiled wire strengthens magnetic field even more
Field strengthened along axis.
Looks just like magnetic field around bar magnet!
“Solenoid”

6. Electromagnets
If you wrap a wire around a non-magnetized piece of iron, then send current through the wire, you can create a magnet that turns on and off!
(The iron becomes a magnet when the electric current is on.)

7. Electromagnets

8. What if we send current through a wire that is already in a magnetic field?
The magnetic fields interact
There will be a FORCE on the wire PERPENDICULAR to the magnetic field

9. Extension of Right Hand Rule
Thumb points in direction of current (or positively charged particles)
Fingers point in direction of magnetic field (N to S)
Palm is direction of force

10. Left Hand for Negative!
For negatively charged particles, like electrons, use your LEFT HAND.

11. Force on Charged Particles
Any flowing charges in a magnetic field will have a force on them
Oscilloscope has a beam of electrons that hit screen – see as dot
Can deflect beam by using magnets
This is the idea behind Cathode Ray tubes on old TV screens

13. Particle Acclerators
Extremely large-scale machines that accelerate elementary particles (like electrons or protons) to extremely high energies (close to the speed of light)
Strong magnets direct and accelerate these charged particles to a target

15. Particle Accelerators
The target (which can be atoms or other elementary particles), is usually located inside a magnetic field in which charged particles are bent.
The bending radius and mass of particle can be used to calculate the particle’s momentum

17. Magnetic Force Equations
The equation for the Force on a charged particle is given by:
Fmag = qBv
Where q = charge (in Coulombs)
B = magnetic field (in Teslas)
v = velocity (in m/s)
then Fmag will be in Newtons

18. Magnetic Force Equations
The equation for the Force on a current-carrying wire in a magnetic field:
Fmag = B I l
Where B = magnetic field (in Teslas))
I = current (in Amps)
l = length of wire in field (m)

19. Loudspeakers Sound signal converted to electrical signal by microphone
Electrical signal is amplified and sent to speaker

20. How a speaker works
Varying electric current causes varying magnetic force on coil
Alternating force on coil  vibrations on cone
Air vibrates
 sound

21. Motor Effect
We’ve seen that when a current passes through a wire that cuts across a magnetic field, a force occurs on the wire.
This is called the MOTOR EFFECT – when an electric current produces motion

22. Simple Electric Motors

24. Natural question that followed…
We know a current carrying wire can induce a magnetic field…
Can you induce a current by using a magnetic field?

25. Generator Effect
When the motion of a wire in a magnetic field induces an electric current, this is called the GENERATOR EFFECT
DEMO – magnet, wire and ammeter

26. Electromagnetic Induction
Inducing a current in a circuit by changing the magnetic field that passes through the circuit
No battery or power source needed!

27. Electromagnetic Induction

28. Generators

29. Recap: Motors
Motors are machines that convert electrical energy into mechanical energy
Current is supplied to loop by voltage source
Magnetic Force on current loop causes it to rotate

30. Recap: Generators
Generators are devices that convert mechanical energy into electrical energy
Turbines (connected to wire loop) are turned in some way in magnetic field
By moving water in hydroelectric plant
By rising steam (water heated up) in coal, natural gas, nuclear plant

31. Bar Magnet Into Coil of Wire
Induced current produces it’s own magnetic field in OPPOSITE direction of the increasing magnetic field.
We don’t get something for nothing by increasing the number of loops. It gets more difficult to push the magnet into coil with more loops.

32. Lenz’s Law
Magnet falling through tube induces a current in the tube. This current creates its own magnetic field, and thus a force that opposes its falling
Lenz’s Law: “An induced current is always in such a direction as to oppose the motion or change causing it”

33. Explaining Lenz’s Law

34. Another way of inducing voltage
When switch on primary is closed, current flows through primary
 A brief surge of current flow through secondary
When switch is opened, another brief surge, but in opposite direction
A change in magnetic field of primary induces voltage in secondary

35. Improving on the design..
Placing an iron core inside coils intensifies magnetic field
Using AC current eliminates need to turn on and off

36. Improving even more… Even more efficient with an iron loop
Changing the number of turns in the coil allows you to change the voltage on the secondary

37. Transformer
A device for increasing or decreasing voltage through electromagnetic induction
Works by inducing a changing magnetic field in one coil which induces an AC current in a nearby secondary coil
Voltages can be STEPPED UP or STEPPED DOWN with a transformer

38. Transformer Equations
Primary Voltage = Secondary Voltage
# of Primary turns # of Secondary turns
You DON’T get something for nothing!
ELECTRIC POWER IN = ELECTRIC POWER OUT
(voltage x current)primary = (voltage x current)sec.

39. Np = Vp
Ns Vs

40. Transmitting Electrical Power
Most electrical power is transmitted in AC not DC because it’s relatively easy to step up and step down voltages with transformers.

41. Transmitting Electrical Power
Over great distances, power is transmitted at high voltages and low currents (more efficient, less heat lost)
120,000 V from power plants to cities
2400 V in cities
120 V to house

42. Another extension of electromagnetism
If I shake a stick back and forth in water, I get waves on water surface
If I shake a charged rod back and forth, we get something called
ELECTROMAGNETIC WAVES

43. Electromagnetic Waves
A moving electric charge is known as electric current
Surrounding this moving charge is a changing magnetic field
This changing magnetic field creates a changing electric field
These regenerate each other
No medium is required

45. Electromagnetic Waves
James Clerk Maxwell first saw this connection between electrical and magnetic fields
He developed a series of equations that showed that electricity, magnetism, and even light were manifestations of the same phenomenon:
The electromagnetic field

46. Electromagnetic Waves
All EM waves consist of oscillating electric and magnetic fields, which radiate outwards at the speed of light
There exist a wide range of frequencies and wavelengths of these EM waves
We call this the ELECTROMAGNETIC SPECTRUM
Visible light is simply EM waves in the range of frequencies our eyes can sense!

47. Electromagnetic Waves
Radio waves
Microwaves
Infrared Waves
Visible Light
Ultraviolet Waves
X-Rays
Gamma Rays
All of these waves travel at
c = x 108 m/s
300,000,000 m/s