chapter 3 electromagnetism

Longman Project! Overhead Transparencies Physics Form

5

Pearson Malaysia Sdn.Bhd. 2007

CHAPTER

333

44

Electromagnetism

3.1 Analysing the Magnetic Effect of a Currentcarrying Conductor

Magnetic Effect of a Currentcarrying Conductor

(a) Electric bell

(b) Magnetic relay

switch

current

electromagnet

pulled byelectromagnet

spring

contact point

contact screwarmature

hammer

gong

+

battery

output

input

contact switch

fulcrum

armature

electromagnet

pulled by electromagnet

+


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CHAPTER

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Electromagnetism

3.1 Analysing the Magnetic Effect of a Current-carrying Conductor

Magnetic Field

S N

N N S S

N S

S

Nbehaveslikea bigmagnet

earth's magnetic field


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CHAPTER

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Electromagnetism


Magnetic Field By Current-carrying Conductors

(a) Straight wire

(b) Coil

(c) Solenoid

I Icurrent

+ +

X X

+

X

+I I I I

+

Electric current is coming out

direction of magnetic field is anti-clockwise

SN

I

+

Umagnetic field

Battery

current


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CHAPTER

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Electromagnetism


Maxwells Right Hand Rule

I

Direction ofmagnetic field

Direction ofcurrent

I

Direction ofcurrent

I I


N

X

X Electric current is going in

direction of magnetic field is clockwise

UN

I

S

+

Battery

current



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CHAPTER

333

48

Electromagnetism

3.2 Understanding the Force on a Current-carrying Conductor ina Magnetic Field

Force on a Current-carrying Conductor in a Magnetic Field

Flemings left hand rule

Force in a lastic (catapult) field

Generating force in a magnetic field

uniform fieldfrom magnet

concentric fieldby electric current

stretching of magneticfield to produce a force

ForceXX+ =

south polemagnadur magnet

metal rod taped

+

wooden block

north pole

light conductor

MI

I

I

F

M

F

I

F (force)

I (current)M (magnetic field)

permanent magnet

wire coil

carbonbrush

Direction of turning

commutator

rheostat

battery

SN

+

Direction of turning

B

permanent magnet

wirecoil

rotating slip-rings

A.C.

carbon brushes

NSA


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CHAPTER

333

49

Electromagnetism

3.2 Understanding the Force on a Current-carrying Conductor ina Magnetic Field

Principle of Motor

A.C. MOTOR

D.C. MOTOR

FARADAYS LAW


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CHAPTER

333

50

Electromagnetism

3.3 Analysing Electromagnetic Induction

Electromagnetic Induction

Cutting the magnetic flux produces electric current

Flemings right hand rule

magnadur magnet

metal rod

GI

Movement of rod

wire

galvanometerInduced current

S N

M

I

FMagnetic field

Motion

Electric current


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CHAPTER

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Electromagnetism


Electromagnetic Induction

N

solenoidpush in

magnet

GI Induced

current

galvanometer

N S

Inducedcurrent

galvanometer

S

pull out

magnet

GI

N S

LENZS LAW

Same magnetic pole produced generatesa repulsive force

Opposite magnetic pole produced generates anattractive force


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CHAPTER

333

52

Electromagnetism


Current Generator

A.C. GENERATOR

Induced e.m.f.

Number ofrevolution

O 34

14

12

1

Turning

B

strongmagnet

slip-rings

Load

carbon brushes

N

SA

Q

P

wirecoil


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CHAPTER

333

53

Electromagnetism


Current Generator

D.C. GENERATOR

S

BN

QP

I

AN

strongmagnet

carbonbrush

Turning

commutator+

wirecoil

directcurrent

Induced e.m.f.

Number ofrevolution O 1

434

12

1

Load-

+


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CHAPTER

333

54

Electromagnetism

3.4 Analysing Transformers3.5 Understanding the Generation and

Transmission of Electricity

Transformer

Symbol

Vp primary voltageVs secondary voltageNp number of turns in

primary coilNs number of turns in

secondary coilIp primary currentIs secondary current

Principle of transformer

1 Voltage V Number of turns N

= =

2 With no power loss P = IpVp = IsVs

3 Efficiency = 100%

= 100%VsIsVpIp

power outputpower input

IpIs

NsNp

VsVp

laminated soft-iron

secondarycoil

primarycoil

Np Ns

A.C. input A.C. output

Vp Vs

IpIs200

800

primary secondary

Structure


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CHAPTER

333

55

Electromagnetism



Type of transformer

Vs > VpNs > Np

VsVp NsNp

Vs < VpNs < Np

VsVp NsNp

step-down transformer

11 kV 480 V 240 VLocal stations

11 kV

11 kV

240 V Houses

33 kV

25 kV

11 kVstep-downtransformer

step-uptransformer

powerstation

132 kV

33 kV

power cableat 33 kV

132 kV

Step-up transformer Step-down transformer

National grid transmission system


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CHAPTER

333

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Electromagnetism



Moving Coil Galvanometer (for D.C. only)

N S

Radial field Advantages

Sensitive Linear scale Can be adapted to become an

ammeter or a voltmeter

AI I

B

R

rIo Io

(I- Io)

I- Io I- Ioshunt

shunt

R = =VGIor

As an ammeter

A BRIo Io

Io Io

VR VG

R = V-VGV-Ior=

V

multiplier

r

As a voltmeter

r = internal resistance of galvanometerIo = maximum current for full-scale deflectionVG = maximum p.d. across galvanometer

pointer

rectangular coil

semicircular magnet

linear scalespring

springsoft-iron core

I

D.C.

SN

S


5


CHAPTER

333

57

Electromagnetism



Instruments for Measuring Electric Current (for D.C. and A.C.)

pointernon-linear scale

silk thread

zero adjustor

adjusting screwplatinumwire

shunt

A B

+ - II

pointer

permanentiron plate

terminal T1 terminal T2

bearing

bearing

solenoid

movable iron plate

fine spring

non-linear scale

shaft

Hot-wire meter

Moving-iron meter

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chapter 3 electromagnetism

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