Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Power engineering wikipedia , lookup
Electromagnetic compatibility wikipedia , lookup
Wireless power transfer wikipedia , lookup
Transformer wikipedia , lookup
Induction motor wikipedia , lookup
History of electric power transmission wikipedia , lookup
Electrification wikipedia , lookup
History of electromagnetic theory wikipedia , lookup
Electric machine wikipedia , lookup
Skin effect wikipedia , lookup
Alternating current wikipedia , lookup
HolisticTuition Home Form 5 Physics Next > The study of matter 1 End CashPlants Chapter 3: Electromagnetism HolisticTuition Physics: Chapter 3 Home Objectives: (what you will learn) < Back Next > 2 End CashPlants 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 HolisticTuition Home 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-pole S-pole Line of force < Back Next > Pilotsweb.com Stargazers 3 End CashPlants Magnetic field around a bar magnet Magnetic field around the Earth HolisticTuition Home 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. < Back Next > 4 End CashPlants The direction of field can be obtained by moving a compass around the wire. HolisticTuition Home 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 < Back Next > 5 End CashPlants Current down: Current going into paper As distance from wire increases, magnetic field gets weaker (as shown by increasing distance between lines). HolisticTuition Home < Back Next > 6 End CashPlants Magnetic effect Without compass, the direction of magnetic field can be obtained using Right-Hand Grip Rule. 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. HolisticTuition Home Solenoid Current, I in circular coil creates magnetic field where it is strongest along the axis. < Back Next > 7 End CashPlants 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. The direction of the field, B is determined using right-hand grip rule (R.H.). HolisticTuition Home Solenoid Solenoids are important because they can create controlled magnetic fields and can be used as electromagnets. < Back Next > 8 End CashPlants 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. This slide for extra information only. HolisticTuition Home Solenoid The magnetic field inside a solenoid is given by: B = µnI B = magnetic field magnitude (teslas) µ = magnetic permeability (henries/meter or newtons/ampere2) n = turns density (number of turns/meter) I = current (amperes) < Back Next > 9 End CashPlants n=N/h N = number of turns h = length of solenoid (meters) µ = ku0 magnetic constant or permeability of free space, µ0 = 4π x 10-7 H/m k = relative permeability HolisticTuition Home < Back Next > 10 End CashPlants 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. HolisticTuition Home Electromagnet 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) < Back • when the current in the coil is increased (I) Next > B = µnI where µ = ku0 µ0 = 4π x 10-7 H/m (or N/A2) k = relative permeability of iron is about 200, steel over 800 11 End CashPlants Electromagnets are used in electric bells, circuit breakers, electromagnetic relays, telephone earpieces, etc. HolisticTuition Home The direction of the force F on the conductor can be obtained using Fleming’s left-hand motor rule. < Back Next > 12 Magnetic force End CashPlants Field, B Current, I Force, F (Motion) HolisticTuition Home Electromagnetic 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 induction < Back Next > 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. 13 End CashPlants 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. HolisticTuition Home The direction of e.m.f. induced or the induced current I can be obtained using Fleming’s right-hand dynamo rule. < Back Next > 14 Electromagnetic induction End CashPlants Force, F (Motion) Field, B Current, I HolisticTuition Home Electromagnetic induction Lenz’s law The direction of the induced current produces an effect that opposes the change in the magnetic flux. < Back Next > 15 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. End CashPlants Induced current produces N-pole to repel the N-pole of magnet HolisticTuition Home Transformers Transformer is an application of electromagnetic induction. It consists of a primary coil and a secondary coil wound on a soft iron core. < Back Next > 16 End CashPlants 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. HolisticTuition Home Generation of Electricity Many sources of energy are used to generate electricity, each with their own advantages and disadvantages. < Back Next > 17 End CashPlants 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. HolisticTuition Home Generation of Electricity Many sources of energy are used to generate electricity, each with their own advantages and disadvantages. < Back Next > 18 End CashPlants 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. HolisticTuition Home 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. < Back Next > Transmission at high voltage reduces current in cables; thus reducing power loss greatly. 19 End CashPlants Power loss as heat in cables = I2R HolisticTuition Home Transmission of Electricity Voltage is stepped down in stages to, say 240 V using transformers before supplying to consumers. < Back Next > The National grid network is an interconnection of various power stations in the country. 20 End CashPlants 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 HolisticTuition Summary Home What you have learned: < Back 21 End CashPlants 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 Thank You