Home End HolisticTuition CashPlants Chapter 3: Electromagnetism Form 5 1 Physics Next > The study of matter
Home End HolisticTuition CashPlants Objectives: (what you will learn) Objectives: (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 Physics: Chapter 3 2 < Back Next >
Home End HolisticTuition CashPlants 3 < Back Next > Line of Force A line of force in magnetic field represents path of free N-pole in magnetic field. Direction of line of force: N-poleS-pole Magnetic field around a bar magnet Magnetic field around the Earth Line of force Pilotsweb.com Stargazers
Home End HolisticTuition CashPlants 4 < Back Next > Magnetic effect When 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. The direction of field can be obtained by moving a compass around the wire.
Home End HolisticTuition CashPlants 5 < Back Next > Magnetic effect The 2-dimensional view of magnetic field due to 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).magnetic field
Home End HolisticTuition CashPlants 6 < Back Next > Magnetic effect 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 field can be obtained using Right-Hand Grip Rule.
Home End HolisticTuition CashPlants 7 < Back Next >Solenoid Current, I in circular coil creates 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 many circular 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.
Home End HolisticTuition CashPlants 8 < Back Next >Solenoid 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. Solenoids are important because they can create controlled magnetic fields and can be used as electromagnets. electromagnets
Home End HolisticTuition CashPlants 9 < Back Next >Solenoid The magnetic field inside a solenoid is given by:magnetic field B = µnI B = magnetic field magnitude (teslas) µ = magnetic permeability (henries/meter or newtons/ampere 2 ) 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. µ = ku 0 magnetic constant or permeability of free space, µ 0 = 4 π x 10 -7 H/m permeability k = relative permeability
Home End HolisticTuition CashPlants 10 < Back Next >Electromagnet An 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. 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.
Home End HolisticTuition CashPlants 11 < Back Next > when the number of turns 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 of soft iron core ( µ ) The strength of the electromagnet increases when the current in the coil is increased ( I ) Electromagnet B = µnI where µ = ku 0 µ 0 = 4 π x 10 -7 H/m (or N/A 2 ) k = relative permeability of iron is about 200, steel over 800
Home End HolisticTuition CashPlants 12 < Back Next > Magnetic force The direction of the force F on the conductor can be obtained using Flemings left-hand motor rule. Force, F (Motion) Field, B Current, I
Home End HolisticTuition CashPlants 13 < Back Next > Electromagnetic induction 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.
Home End HolisticTuition CashPlants 14 < Back Next > Electromagnetic induction The direction of e.m.f. induced or the induced current I can be obtained using Flemings right-hand dynamo rule. Force, F (Motion) Field, B Current, I
Home End HolisticTuition CashPlants 15 < Back Next > Electromagnetic induction Lenzs law The 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 Lenzs law. Induced current produces N-pole to repel the N-pole of magnet
Home End HolisticTuition CashPlants 16 < Back Next >Transformers 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.
Home End HolisticTuition CashPlants 17 < Back Next > Generation 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 energy Natural 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.
Home End HolisticTuition CashPlants 18 < Back Next > Generation 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 energy Natural 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.
Home End HolisticTuition CashPlants 19 < Back Next > Transmission 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. Transmission at high voltage reduces current in cables; thus reducing power loss greatly. Power loss as heat in cables = I 2 R
Home End HolisticTuition CashPlants 20 < Back Next > Transmission of Electricity Voltage is stepped down in stages to, say 240 V using transformers before supplying to consumers. The National grid network is an interconnection of various power 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
Home End HolisticTuition CashPlants 21 Summary < Back What you have learned: 1.magnetic effect of current-carrying conductor Thank You 2. 2.force on current-carrying conductor in magnetic field 3. 3.electromagnetic induction 4. 4.transformers 5. 5.generation & transmission of electricity