F5C3 Electromagnetism

8/4/2019 F5C3 Electromagnetism

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Chapter 3:Chapter 3:

ElectromagnetismElectromagnetism

Form 5Form 5

1

PhysicsPhysics

Next >

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

2

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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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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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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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F5C3 Electromagnetism