Electromagnetism. We found out earlier that electric charges produce electric force fields

 So what is a magnetic field?

Magnetic Field

 So how are magnetic fields produced?

This experiment shows that the moving electrons in the wire also produce a…… Magnetic Field

 So electric charges always produce an electric field.  If the electric charges are moving, they also produce a magnetic field

Wire with electrons flowing OUT Produces circular magnetic field

  GRIP RULE   Fingers curl in direction of thing going round a circle   Thumb points in the direction of thing going straight

Left Hand Grip Rule for Wires Electron flow Magnetic field

What direction do the electrons flow?

Magnetic field Electron flow GRIP RULE Fingers curl in direction of thing going round a circle Thumb points in the direction of thing going straight Left Hand Grip Rule for Coils

What direction is the field in the coil? Which end is North??

Electrons Moving in Fields 200 Volts

 link to cathode ray tube link to cathode ray tube link to cathode ray tube

Magnetic Force on Electrons

electron flow SLAP Magnetic force on electron (out of page) Magnetic field

electron flow magnetic field FORCE

Find the direction of the Magnetic Force xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxx xxxxxxxxxxxxxxxxxxxxx

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxx xxxxxxxxxxxxxxxxxxxxx

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxx xxxxxxxxxxxxxxxxxxxxx ELECTRON COMING OUT

Trajectory of a Moving Electron Electrons cutting across a magnetic field bend in a circle

 LINK TO CHARGE IN A MAGNETIC FIELD LINK TO CHARGE IN A MAGNETIC FIELD LINK TO CHARGE IN A MAGNETIC FIELD

 The size of the magnetic force on a charge depends on:  The strength of the magnetic field.  The speed of the charge across the field  The amount of charge

B = T 3.0x10 6 ms -1 Find the size and direction of the Magnetic Force

B = T 3.0x10 6 ms -1 Find the size and direction of the Magnetic Force

B = T 3.0x10 6 ms -1 Find the size and direction of the Magnetic Force

 link to F=Bvq link to F=Bvq link to F=Bvq

Magnet on a TV

Aurora, Invercargill

Aurora, Antarctica

LHC Cern circumference = 27 km depth= 100 m

Proton Tube

Particle Detector

What keeps the protons going in a circle? If the protons go clockwise, what direction is the magnetic field??

Your Particle Accelerator

CRT. Electrons can be deflected using electric OR magnetic fields

Colour Monitor

 link to electrons in a TV link to electrons in a TV link to electrons in a TV  link to TV link to TV link to TV

Ex. Proton mass = 1.67 x kg. Proton charge = 1.6 x C Circumference = 27 km calculate the magnetic field strength required when the protons are travelling at 0.99c

Extension: there is a flaw in your calculation, what is it????

 Measuring the mass of an electron with a “magic eye tube”

No magnetic field

small magnetic field

large magnetic field

 By measuring the radius of the curve, we can calculate the magnetic field strength.

Force on a Current Carrying Wire Electron flow 1: electrons in roller are moving... 2: causing electrons to be pushed… 3: causing roller to be pushed…… This is called the motor effect current flow

electron motion (this is the moving wire) SLAP Magnetic force on electron (this is the current) Magnetic field

The size of the electromagnetic force depends on: 1. Strength of magnetic field 2. Current in wire 3. Length of wire

Applications  Thousands of devices use this force to do something useful, e.g.  The electric motor in……

The speakers in your phone or stereo

ELECTRIC MOTOR ELECTRIC CURRENT Magnet + Wire MOTION

current flow

 link to Fendt Electric Motor link to Fendt Electric Motor link to Fendt Electric Motor

Parts of a Motor

World’s Simplest Motor - + Mag Field e - flow

Loudspeaker

The Current into a Speaker is Alternating

NS AC from amplifier

NS NPUSH Electron flow S

NS AC from amplifier S PULL N

NS

 We have seen that…… ELECTRIC MOTOR ELECTRIC CURRENT Magnet + Wire MOTION Electromagnetic Induction

 Do you think that…… If you move a wire through a magnetic field you can produce electric current? ELECTRIC MOTOR ELECTRIC CURRENT Magnet + Wire MOTION

 Here’s a hint  Tyger Tyger, burning bright, In the forests of the night; What immortal hand or eye,  Could frame thy fearful symmetry

Remember this? xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxx xxxxxxxxxxxxxxxxxxxxx Electron motion Force

How about moving a wire full of electrons across a magnetic field? xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxx xxxxxxxxxxxxxxxxxxxxx Electron motion Force on electrons + _ Move the wire

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxx xxxxxxxxxxxxxxxxxxxxx Electron motion Force on electrons + _ There is a voltage induced across the wire

 This is called……… Electromagnetic Induction It is used to generate almost all the electricity you use.

It is also used in things like ……

Voltage Induced in Moving Wire 1: electrons in roller are moving 2: causing them to be pushed 3:The bottom end (X) becomes negative (Y becomes positive) X Y 4:There is an induced voltage

 The size of the induced voltage depends on: 1. Strength of magnetic field 2. Speed or wire across the magnetic field 3. Length of wire

 link to Fendt Generator link to Fendt Generator link to Fendt Generator

Motor Effect and Generator Effect Electron flow Force on roller 1: electrons in roller are moving 2: causing them to be pushed 3: electrons in roller are now flowing 4: causing them (and roller) to be pushed

diagram shows conventional current

Microphone NS AC to amplifier

Sound waves vibrate coil N S

This causes alternating current

 We have seen that…… ELECTRIC MOTOR ELECTRIC CURRENT Magnet + Wire MOTION Generator MOTION Magnet + Wire ELECTRIC CURRENT

SPEAKER ALTERNATING CURRENT Magnet + Wire SOUND MICROPHONE SOUND Magnet + Wire ALTERNATING CURRENT

 Extension  James Clerk Maxwell showed that……  a changing electric field created a changing magnetic field.  and a changing magnetic field created a changing electric field.

 he worked out these fields would travel through space at a speed of ……… 3.0 x 10 8 ms -1