Presentation on theme: "Chapter 9: MAGNETISM AND ELECTROMAGNETIC INDUCTION"— Presentation transcript:
1Chapter 9: MAGNETISM AND ELECTROMAGNETIC INDUCTION
2This lecture will help you understand: Magnetic PolesMagnetic FieldsMagnetic DomainsElectric Currents and Magnetic FieldsMagnetic Forces on Moving ChargesElectromagnetic InductionGenerators and Alternating CurrentPower ProductionThe Transformer—Boosting or Lowering VoltageField Induction
3Magnetic Poles Magnetic poles are in all magnets: you can’t have one pole without the otherno single pole known to existExample:simple bar magnet—poles at the two endshorseshoe magnet: bent U shape—poles at ends
4Magnetic Poles Magnetic force force of attraction or repulsion between a pair of magnets depends on which end of the magnet is held near the otherbehavior similar to electrical forcesstrength of interaction depends on the distance between the two magnets
5Magnetic Poles Magnetic poles give rise to magnetic force two types interacting with each othernorth pole (north-seeking pole)south pole (south-seeking pole)Rule for magnetic forces between magnetic poles:Like poles repel; opposite poles attract
6Magnets CHECK YOUR NEIGHBOR A weak and strong magnet repel each other. The greater repelling force is by theA. stronger magnet.weaker magnet.Both the same.None of the above.C. Both the same.
7Magnets CHECK YOUR ANSWER A weak and strong magnet repel each other. The greater repelling force is by theA. stronger magnet.weaker magnet.Both the same.None of the above.Explanation:Remember Newton’s third law!C. both the same.
8Magnetic Fields Magnetic fields: occupy the space around a magnet produced by moving electric chargesField shape revealed by magnetic field lines that spread from one pole, curve around magnet, and return to other poleLines closer together field strength is greater
9Magnetic Fields Magnetic fields produced by two kinds of electron motionelectron spinmain contributor to magnetismpair of electrons spinning in same direction creates a stronger magnetpair of electrons spinning in opposite direction cancels magnetic field of the otherelectron revolution
10Magnetic Domains Magnetic domains • clustered regions of aligned atoms oriented in random fashion — magnetic fields produced by each can cancel the fields of other.When oriented in one direction, then the substance containing them is a magnet• Magnet strength depends on number of magnetic domains that are aligned.
12Electric Currents and Magnetic Fields Connection between electricity and magnetismMagnetic field forms a pattern of concentric circles around a current-carrying wirewhen current reverses direction,the direction of the field linesreverse
14Electric Currents and Magnetic Fields Magnetic field intensityincreases as the number of loops increase in a current-carrying coil
15Electric Currents and Magnetic Fields CHECK YOUR NEIGHBORAn electromagnet can be made stronger byA. increasing the number of turns of wire.increasing the current in the coil.Both A and B.None of the above.C. Both A and B.
16Electric Currents and Magnetic Fields CHECK YOUR ANSWERAn electromagnet can be made stronger byA. increasing the number of turns of wire.increasing the current in the coil.Both A and B.None of the above.C. Both A and B.
17Magnetic Forces on Moving Charges Charged particles moving in a magnetic field experience a deflecting force—greatest when moving at right angles to magnetic field lines.
19Magnetic Force and Levitation When an upward magnetic force is greater than gravity, then an object can levitate.A magnetically levitated vehicle is shown in the figure to the right – a magplane.No friction, no vibrations
20Magnetic Force in Space Earth’s magnetic field deflects many charged particles that make up cosmic radiation.
21Magnetic Force CHECK YOUR NEIGHBOR The magnetic force on a moving charged particle can change the particle’sA. speed.direction.Both A and B.Neither A nor B.B. direction.
22Magnetic Force CHECK YOUR ANSWER The magnetic force on a moving charged particle can change the particle’sA. speed.direction.both A and B.neither A nor B.Explanation:Only an electric force can change the speed of a charged particle. Since the magnetic force acts at right angles to velocity, it can only change the direction of a moving charged particle.B. direction.
23Magnetic Force on Moving Charges Electric metersdetect electric currentExamples:magnetic compasscompass in a coil of wires
24Magnetic Force on Moving Charges Galvanometercurrent-indicating device named after Luigi Galvanicalled ammeter when calibrated to measure current (amperes)called voltmeter when calibrated to measure electric potential (volts)
25Magnetic Force on Moving Charges Electric motordifferent from galvanometer in that each time the coil makes a half rotation, the direction of the current changes in cyclic fashion to produce continuous rotation
26Motor and Generator CHECK YOUR ANSWER A motor and a generator areA. similar devices.very different devices with different applications.forms of transformers.energy sources.A. similar devices.
27Motor and Generator CHECK YOUR ANSWER A motor and a generator areA. similar devices.very different devices with different applications.forms of transformers.energy sources.A. similar devices.
28Electromagnetic Induction discovered by Faraday and Henryvoltage is induced with change of magnetic field strength in a coil of wire
29Electromagnetic Induction Electromagnetic induction (continued)induced voltage can be increased byincreasing the number of loops of wire in a coilincreasing the speed of the magnet entering and leaving the coilslow motion produces hardly any voltagerapid motion produces greater voltage
30Electromagnetic Induction Induction occurs whether the magnetic field moves past the wire or the wire moves through the magnetic field.
31Electromagnetic Induction More loops; more induction
32Electromagnetic Induction Faraday’s lawthe induced voltage in a coil is proportional to the number of loops, multiplied by the rate at which the magnetic field changes within those loopsamount of current produced by electromagnetic induction is dependent onresistance of the coilcircuit that it connectsinduced voltage
33Electromagnetic Induction More difficult to push the magnet into a coil with many loops because the magnetic field of each current loop resists the motion of the magnet.
34Electromagnetic Induction CHECK YOUR ANSWERThe resistance you feel when pushing a piece of iron into a coil involvesA. repulsion by the magnetic field you produce.energy transfer between the iron and coil.Newton’s third law.resistance to domain alignment in the iron.A. repulsion by the magnetic field you produce.
35Electromagnetic Induction CHECK YOUR ANSWERThe resistance you feel when pushing a piece of iron into a coil involvesA. repulsion by the magnetic field you produce.energy transfer between the iron and coil.Newton’s third law.resistance to domain alignment in the iron.A. repulsion by the magnetic field you produce.
36Generators and Alternating Current opposite of a motorconverts mechanical energy into electrical energy via coil motionproduces alternating voltage and current
37Generators and Alternating Current The frequency of alternating voltage induced in a loop is equal to the frequency of the changing magnetic field within the loop.
38Power ProductionUsing Faraday and Henry’s discovery of electromagnetic induction, Nikola Tesla and George Westinghouse showed that electricity could be generated in sufficient quantities to light cities.
39The Transformer—Boosting or Lowering Voltage input coil of wire —primary powered by AC voltage sourceoutput coil of wire —secondary connected to external circuit
40The Transformer Transformer (continued) both wound on a common iron corethen magnetic field of primary passes through secondaryuses ac in one coil to induce ac in second coil
42Transformers Everywhere This common transformer lowers 120V to 6V or 9V. It also converts AC to DC by means of a diode inside.A common neighborhood transformer that typically steps 2400V down to 240V.
43Transformer Power CHECK YOUR ANSWER A step-up transformer in an electrical circuit can step upA. voltage.energy.Both A and B.Neither A nor B.A. voltage.
44Transformer Power CHECK YOUR NEIGHBOR A step-up transformer in an electrical circuit can step upA. voltage.energy.Both A and B.Neither A nor B.Explanation:Stepping up energy is a conservation of energy no-no!A. voltage.
45Electric PowerElectric power is equal to the product of the voltage and current.
46Electric Grid uses Transformers Voltage generated in power stations is stepped up with transformers prior to being transferred across the country by overhead cables.Then other transformers reduce the voltage before supplying it to homes, offices, and factories.
47Transformer PowerNeglecting heat losses, power into a transformer = power out of transformer.
48Electric Field Induction Basic to electromagnetic induction is that electric and magnetic fields can induce each other.An electric field is induced in any region of spacein which a magnetic field is changing with time.orA magnetic field is induced in any region of spacein which an electric field is changing with time.
49Electric and Magnetic Field Induction CHECK YOUR NEIGHBORThe mutual induction of electric and magnetic fields can produceA. light.energy.sound.None of the above.A. light.
50Electric and Magnetic Field Induction CHECK YOUR ANSWERThe mutual induction of electric and magnetic fields can produceA. light.energy.sound.None of the above.A. light.
51Field InductionLight is produced by the mutual induction of electric and magnetic fieldsspeed of light is the speed of emanation of these fieldstoo slow, the regenerating fields die outtoo fast, fields build up in a crescendo of ever-increasing energyat speed c, just right! And, there is light!