1

John Parkinson John Parkinson ©©

2

THE AURORA

The Aurora Borealis, the Northern Lights and the Aurora Australis, the Southern lights are phenomena

resulting from the interaction between Solar Wind and the Earth’s magnetic field.

3

N S

Lines of magnetic flux, Φ

Magnetic flux density, B, measures the strength of the magnetic field.

B = number of lines of flux per square metre

AB

UNITS are Webers per square metre Wb m-2 or TESLAS (T)

B IS A VECTOR QUANTITY

4

N S

Lines of magnetic flux, Φ

AB

A

Total magnetic flux through area A is given by:

Φ = B A webers, when the area is perpendicular to the field

Aθ

Φ = B A sinθ

5

geographic north

geographic north

magnetic north

s

N

6

1820Professor Oersted was demonstrating an experiment for students when he accidentally discovered that a compass needle moved when it was close to a wire connected to a battery.

Professor Hans Christian Oersted

7

B

I

8

I

B

9

RIGHT HAND GRIP RULE:

I

10

current outwards current inwards

r

B

r

IB

20

-

11

length l

IN turns

In the middle

l

NIB 0

at the end l

NIB

20

12

N S

Interaction between a magnet and the field due to a current

N S

13

N S

F

14

FLEMING’S LEFT HAND MOTOR RULE

FOREFINGER = FIELD

THUMB = MOTION

SECOND FINGER = CURRENT

15

FLEMING’S LEFT HAND MOTOR RULE

FOREFINGER = FIELD

THUMB = MOTION

SECOND FINGER = CURRENT

16

N S

I

B

F

F = B I lWhere l = length of conductor in the field

17

S N

HAIR SPRINGS CONTROL MOVEMENT AND ALLOW CURRENT TO ENTER AND LEAVE THE COIL

RADIAL SOFT IRON POLE PIECES

COIL

PERMANENT MAGNET

MOVING COIL

METER

SOFT IRON CYLINDER

18

S N+

+

19

N

A

B

D

C

I

S

brushes

EVERY TIME THE COIL PASSES THROUGH THE VERTICAL POSITION, THE COMMUTATOR REVERSES THE CURENT IN THE COIL, IN ORDER TO

SUSTAIN THE ROTATION

DC MOTORC

A

B

SN

D

I

Split ring commutator

20

LOUDSPEAKER

N

S

N

Solenoid on paper cone is forced to vibrate - left hand rule

magnet

S

N

N N

N

magnet

AC signalcoil

21

22

Force experienced by a charged particle (charge Q) moving with a velocity, v in a magnetic field of Flux density, B

+Q

B

I

A

B

l

Particle travels l metres from A to B in t seconds

F

F = B I l

t

QI

t

BQlF

but vt

l

F = B Q v

23

+ I

FF THE FORCE IS ALWAYS

PERPENDICULAR TO THE MOTION

THE PARTICLE MUST MOVE

ALONG AN ARC OF A CIRCLE

r

mvBQv

2

BQ

mvrarcofradius ,

+

24

Frequency of Rotation, f

x x x x x x x x x x x xx x x x x x x x x x x xx x x x x x x x x x x x

x x x x x x x x x x x x x x x x x x x x x x x x

B inwards

+

r

mvBQv

2

rfT

rv

22

r

mvBQ

r

frmBQ

2

m

BQf

2

The frequency is independent of the radius and the velocity

This is the principle of the CYCLOTRON

25

High frequency square wave to accelerate charge across the gap

CYCLOTRON

+High frequency square wavem

BQf

2