Presentation on theme: "Chapter 3: Electromagnetism"— Presentation transcript:
1Chapter 3: Electromagnetism Form 5PhysicsNext >The study of matterChapter 3: Electromagnetism1
2Physics: Chapter 3Objectives: (what 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< BackNext >2
3Line of ForceA line of force in magnetic field represents path of free N-pole in magnetic field. Direction of line of force: N-pole S-poleLine of forceMagnetic field around the Earth< BackNext >Magnetic field around a bar magnetMagnetism and the Magnetic CompassA MAGNET IN SPACEPilotsweb.comStargazers3
4Magnetic effectWhen current flows in a conductor, a magnetic field is produced around it. Magnetic field can be observed by sprinkling iron filings around wire on a piece of cardboard.< BackNext >The direction of field can be obtained by moving a compass around the wire.4
5Magnetic effectThe 2-dimensional view of magnetic field due to current in straight wire is easier to draw.Current up: Current coming out of paperCurrent down: Current going into paper< BackNext >As distance from wire increases, magnetic field gets weaker (as shown by increasing distance between lines).5
6Magnetic effectWithout compass, the direction of magnetic field can be obtained using Right-Hand Grip Rule.< BackNext >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.6
7SolenoidCurrent, I in circular coil creates magnetic field where it is strongest along the axis.Solenoid is formed from many circular coils of wire uniformly wound in the shape of a cylinder through which electric current flows.< BackNext >Magnetic field pattern produced by a current in a solenoid is almost identical to that of a bar magnet.The direction of the field, B is determined using right-hand grip rule (R.H.).7
8SolenoidSolenoids are important because they can create controlled magnetic fields and can be used as electromagnets.< BackNext >To find the N-pole of solenoid, grip it with right hand, the fingers curl in the direction of current, and the thumb points in the direction of N-pole.8
9Solenoid 9 The magnetic field inside a solenoid is given by: B = µnI This slide for extra information only.SolenoidThe magnetic field inside a solenoid is given by:B = µnIB = magnetic field magnitude (teslas)µ = magnetic permeability (henries/meter or newtons/ampere2)n = turns density (number of turns/meter)I = current (amperes)n = N / hN = number of turnsh = length of solenoid (meters)< BackNext >µ = ku0magnetic constant or permeability of free space, µ0 = 4π x 10-7 H/mk = relative permeability9
10ElectromagnetAn electromagnet is made by winding a coil of wire around a soft iron core, which loses its magnetism when the current is switched off, unlike steel which is magnetized permanently.< BackNext >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.10
11Electromagnet 11 The strength of the electromagnet increases significantly with the use of soft iron core (µ)when the number of turns per unit length of the coil is increased (n)< BackNext >when the current in the coil is increased (I)B = µnIwhere µ = ku0µ0 = 4π x 10-7 H/m (or N/A2)k = relative permeability of iron is about 200, steel over 80011Electromagnets are used in electric bells, circuit breakers, electromagnetic relays, telephone earpieces, etc.
12Magnetic forceForce, F(Motion)Field, BCurrent, IThe direction of the force F on the conductor can be obtained using Fleming’s left-hand motor rule.< BackNext >12
13Electromagnetic induction Electromagnetic induction is the production of induced e.m.f. in conductor when there is relative motion between conductor and magnetic field.Faraday’s law of electromagnetic inductionThe e.m.f. induced in a conductor is directly proportional to the rate of change of magnetic flux through the conductor.< BackNext >An e.m.f. is induced if wire cuts across magnetic field.13No e.m.f. is induced if the wire moved parallel to magnetic field; the magnetic lines of forces are not cut by the wire.
14Electromagnetic induction Force, F(Motion)Field, BCurrent, IThe direction of e.m.f. induced or the induced current I can be obtained using Fleming’s right-hand dynamo rule.< BackNext >14
15Electromagnetic induction Lenz’s lawThe direction of the induced current produces an effect that opposes the change in the magnetic flux.An e.m.f. is induced in a solenoid when a magnet is moved into or out of solenoid. The direction of induced current is obtained using Lenz’s law.< BackNext >15Induced current produces N-pole to repel the N-pole of magnet
16TransformersTransformer is an application of electromagnetic induction.It consists of a primary coil and a secondary coil wound on a soft iron core.< BackNext >16Transformer is used to step-up or step-down the voltage of an a.c. supply, depending on where the a.c. source is applied.
17Generation of Electricity Many sources of energy are used to generate electricity, each with their own advantages and disadvantages.Examples:HydroPotential energy of water in a dam converted to kinetic energyNatural gas, diesel, coalUsed as fuel to heat water in boilers to produce steamBiomassWaste material used as fuel, or decomposition of waste for methane gas for use as fuel.Nuclear energyNuclear fission of uranium releases heat used to heat water.SunlightSolar cells convert sunlight into electricity.WindStrong wind rotates windmill-like blades to rotate turbines.< BackNext >17
18Generation of Electricity Many sources of energy are used to generate electricity, each with their own advantages and disadvantages.Examples:HydroPotential energy of water in a dam converted to kinetic energyNatural gas, diesel, coalUsed as fuel to heat water in boilers to produce steamBiomassWaste material used as fuel, or decomposition of waste for methane gas for use as fuel.Nuclear energyNuclear fission of uranium releases heat used to heat water.SunlightSolar cells convert sunlight into electricity.WindStrong wind rotates windmill-like blades to rotate turbines.< BackNext >18
19Transmission of Electricity Alternating voltage is generated at power station as its voltage can be transformed with transformers.A step-up transformer changes voltage to 320 kV or 500 kV.< BackNext >Transmission at high voltage reduces current in cables; thus reducing power loss greatly.Power loss as heat in cables = I2R19
20Transmission of Electricity Voltage is stepped down in stages to, say 240 V using transformers before supplying to consumers.< BackNext >The National grid network is an interconnection of various power stations in the country.It ensures:minimal disruption to power supply through fast backupsefficient power generation by matching demand with supplythat power stations can shut down for regular maintenance20
21Summary 21 What you have learned: Thank You magnetic effect of current-carrying conductor2. force on current-carrying conductor in magnetic field< Back3. electromagnetic induction4. transformers5. generation & transmission of electricity21Thank You