f5c3 electromagnetism
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Chapter 3:Chapter 3:
ElectromagnetismElectromagnetism
Form 5Form 5
1
PhysicsPhysics
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The study of matterThe study of matter
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Objectives:Objectives:((what you will learnwhat you will learn))
1) magnetic effect of current-carrying conductor
2) force on current-carrying conductor in
magnetic field
3) electromagnetic induction
4) transformers
5) generation & transmission of electricity
Physics: Chapter 3Physics: Chapter 3
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Line of ForceLine of Force
Aline of force in magnetic field represents path offree N-pole in magnetic field.
Direction of line of force: N-pole S-pole
Magnetic field around a bar magnet Magnetic field around the Earth
Line of force
Pilotsweb.com
Stargazers
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MagneticeffectMagneticeffect
When current flows in a conductor, a magneticfield is produced around it.
Magnetic field can be observed by sprinkling iron
filings around wire on a piece of cardboard.
The direction
of field can be
obtained bymoving a
compass
around the
wire.
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MagneticeffectMagneticeffect
The 2-dimensional view of magnetic field dueto current in straight wire is easier to draw.
Current up: Current coming out of paper
Current down: Current going into paper
As distance from wire
increases, magnetic field gets
weaker(as shown by increasing
distance between lines).
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MagneticeffectMagneticeffect
Right-Hand Grip Rule
Grip wire with the right hand and with the thumb
pointing in the direction of current. The other fingers
point in the direction of magnetic field.
Without
compass, the
direction of
magnetic fieldcan be
obtained using
Right-Hand
Grip Rule.
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SolenoidSolenoidCurrent,Iin circular coilcreates magnetic field where
it is strongest along the axis.
The direction of
the field, B is
determined using
right-hand grip
rule (R.H.).
Solenoid is formed from manycircular coils of wire uniformly
wound in the shape of a cylinder
through which electric current
flows.
Magnetic field pattern produced
by a current in a solenoid is
almost identical to that of a bar
magnet.
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SolenoidSolenoid
To find the N-pole of
solenoid, grip it withright hand, the fingers
curl in the direction of
current, and the
thumb points in the
direction of N-pole.
Solenoids are
important
because they
can create
controlled
magnetic fields
and can be usedas
electromagnets.
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SolenoidSolenoidThe magnetic field inside a solenoid is given by:
B = nI
B = magnetic field magnitude (teslas)
= magnetic permeability (henries/meter or newtons/ampere2)
n = turns density (number of turns/meter)
I= current (amperes)
n =N/ h
N= number of turns
h = length of solenoid (meters)
This slide for extra information only.
=ku0magnetic constant or
permeability of free space,
0 = 4x 10-7 H/m
k=
relative permeability
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ElectromagnetElectromagnetAn
electromagnet
is made by
winding a coil of
wire around a
soft iron core,
which loses itsmagnetism when
the current is
switched off,
unlike steel
which ismagnetized
permanently.
In electromechanical devices, direct current is used
to create strong magnetic field for drawing iron core
or plunger into it, such as in switches and relays.
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when the number ofturns per unit length of the
coil is increased (n)
Electromagnets are used in electric bells, circuit breakers,
electromagnetic relays, telephone earpieces, etc.
significantly with the use ofsoft iron core ()
The strength of the electromagnet increases
when the current in the coil is increased (I)
ElectromagnetElectromagnet
B = nI
where =ku00 = 4x 10
-7 H/m (or N/A2)
k= relative permeability of iron is about 200, steel over 800
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Magnetic forceMagnetic force
The direction of the force
Fon the conductor can
be obtained using
Flemings left-handmotorrule.
Force,F(Motion)
Field, B
Current, I
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ElectromagneticinductionElectromagneticinduction
Electromagnetic induction is the production of
induced e.m.f. in conductor when there is relative
motion between conductor and magnetic field.
Faradays law of electromagnetic induction
The e.m.f. induced in a conductor is directly
proportional to the rate of change of magnetic flux
through the conductor.
An e.m.f. is induced if wire cuts across magnetic field.
No e.m.f. is induced if the wire moved parallel to magnetic
field; the magnetic lines of forces are not cut by the wire.
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ElectromagneticinductionElectromagneticinduction
The direction of e.m.f.
induced or the induced
current Ican be obtained
using Flemings right-handdynamo rule.
Force,F
(Motion)
Field, B
Current, I
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TransformersTransformers
Transformer is an application of electromagnetic induction.It consists of a primary coil and a secondary coil wound on a
soft iron core.
Transformer is used to step-up or step-down the voltage of an
a.c. supply, depending on where the a.c. source is applied.
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Generation of ElectricityGeneration of Electricity
Many sources of energy are used to generate electricity, each
with their own advantages and disadvantages.
Examples:
Hydro
Potential energy of water in a dam converted to kinetic energyNatural gas, diesel, coal
Used as fuel to heat water in boilers to produce steam
Biomass
Waste material used as fuel, or decomposition of waste for
methane gas for use as fuel.
Nuclear energy
Nuclear fission of uranium releases heat used to heat water.
Sunlight
Solar cells convert sunlight into electricity.
Wind
Strong wind rotates windmill-like blades to rotate turbines.
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Generation of ElectricityGeneration of Electricity
Many sources of energy are used to generate electricity, each
with their own advantages and disadvantages.
Examples:
Hydro
Potential energy of water in a dam converted to kinetic energyNatural gas, diesel, coal
Used as fuel to heat water in boilers to produce steam
Biomass
Waste material used as fuel, or decomposition of waste for
methane gas for use as fuel.
Nuclear energy
Nuclear fission of uranium releases heat used to heat water.
Sunlight
Solar cells convert sunlight into electricity.
Wind
Strong wind rotates windmill-like blades to rotate turbines.
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Transmission of ElectricityTransmission of Electricity
Alternating voltage is generated at power station as itsvoltage can be transformed with transformers.
A step-up transformer changes voltage to 320 kV or 500 kV.
Transmission at high voltage reduces current in cables; thus
reducing power loss greatly.
Powerloss as heat in cables =I2R
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Transmission of ElectricityTransmission of Electricity
Voltage is stepped down in stages to, say 240 V usingtransformers before supplying to consumers.
TheN
ationalgri
dnetwork is an interconnection of variouspower stations in the country.
It ensures:
minimal disruption to power supply through fast backups
efficient power generation by matching demand with supply
that power stations can shut down for regular maintenance
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SummarySummary
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hat you have learned:What you have learned:
1. magnetic effect of current-carrying conductor
Thank YouThank You
2.2. force on current-carrying conductor inmagnetic field
3.3. electromagnetic induction
4.4. transformers5.5. generation & transmission of electricity
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