2 Magnetism The Greeks discovered a mineral that had a peculiar property It attracted metals, they found it in a place called Magnesia so they called it magnetic!Magnetism – refers to properties and interactions of magnetsCan be made of iron, cobalt, or nickel
3 Magnetic ForceNot only do magnets attract metal objects, they also exert a force on each otherMagnetic force – the attraction or repulsion felt between magnets
4 Magnetic FieldA magnet is surrounded by a magnetic field which exerts the magnetic forceObjects made of iron or another magnet are within the field it will reactThe field can be shown with lines of force or magnetic field lines
5 Magnetic PolesMagnetic Pole – area of a magnet where the magnetic force exerted is the strongestNorth and South polesNorth pole will point “North” like a compassField lines always connect from north pole to south pole
8 Earth’s Magnetic Poles Earth’s magnetic poles are opposite of what you would think!The N end of a compass needle points north…which means…The north pole of Earth is the south pole of Earth’s magnet!
9 Magnetic DomainMagnetic Domain – groups of atoms aligned with magnetic polesIn a magnet, all magnetic domains are aligned
10 Isolated poles?! Can we break a magnet in two? Sure we can! But what happens to the poles?There will still be a north and south pole!
11 Electricity and Magnetism Sometimes it helps to be lucky…In 1820 a Danish physics teacher was demonstrating electric circuitsHe had left a compass nearby the circuit and noticed as electricity was flowing, the compass was deflectedHe hypothesized that an electric current must produce a magnetic field
12 Right Hand RuleMoving charges flowing through a wire create a magnetic fieldThe field forms a circular pattern around the wireDirection of field depends on the currentThe strength of the field depends on the strength of the current
13 Right Hand RuleThe right hand rule helps determine the direction of the magnetic fieldCurrent = IMagnetic field = B
14 ElectromagnetsElectromagnet – a temporary magnet made by placing a piece of iron inside a current-carrying coil of wireTemporary because they only work while current is flowing
15 Magnets Make Music Speakers work because of electromagnets! Information is read from a CDThat information varies electrical current through a coiled wireThe electromagnet that is created is attracted or repelled by a fixed magnet within the speakerThe causes vibration which creates sound!
16 GalvanometerGalvanometer – a device that uses an electromagnet to measure electric currentOften used for gauges in a carThe greater the current the stronger the electromagnetThe needle will push against a spring to align with the poles of a permanent magnet
17 Electric MotorsElectric motor – device that converts electrical energy into mechanical energyElectric motor contains an electromagnet that can rotate freely inside a permanent magnetWhen current flows the electromagnet produces a magnetic field
18 Electric MotorsBy flipping the flow of the current the poles of the electromagnet are switched and the coil can continue to rotateIn some motors a communicator flips the flow of the currentThe greater the electric current the faster it will spin
19 Question…So we’ve seen that using an electric current and a magnet we can create a running motorWhat if we turned the current off and turned the wire coils ourselves?
20 Electromagnetic Induction Electromagnetic induction – producing an electric current by moving a loop of wire through a magnetic field
21 GeneratorGenerator – produces electric current by rotating a coil of wire in a magnetic field
22 Switching Direction This results in AC electric current! As the coil turns inside of a fixed magnet, the current will switch directionThis results in AC electric current!
23 Power PlantsIn order to generate power for you home and for cities power companies use massive generatorsTurbine – a large wheel pushed by water, wind, or steam
24 Direct vs. Alternating Current Two forms of electric currentDirect current (DC) – flows only in one direction in a wireBatteriesAlternating Current (AC) – flows in 2 directions and alternates direction in a regular wayOutlets in your home60 Hz in N. America
25 Transformers No…not Optimus Prime Transformer – a device that increases or decreases voltage of an alternating current
27 Transformers Step-up transformer Step-down transformer Secondary coil has more turnsThis increases the voltageEx. Primary coil is 60V if the secondary has 2 times the turns the secondary voltage will be 120V60V x 2 = 120VStep-down transformerSecondary coil has fewer turnsThis decreases the voltageEx. Primary coil is 120V and secondary has half as many turns the secondary voltage will be 60V120V x ½ = 60V