2 Electromagnetic Induction Both Michael Faraday (England) and Joseph Henry (U.S.) discovered that electric current could be produced in a wire by simply moving a magnet in or out of a wire coilThe production of voltage depends only on the relative motion of the conductor with respect to the magnetic fieldThe amount of voltage depends on how quickly the magnetic field lines are traversed by the wireElectromagnetic Induction – the phenomenon of inducing a voltage in a conductor by changing the magnetic field near the conductor
4 Faraday’s LawThe induced voltage in a coil is proportional to the product of the number of loops and the rate at which the magnetic field changes within those loops.The amount of current produced by electromagnetic induction depends not only on the induced voltage but also on the resistance of the coil and the circuit to which it is connected
6 Generators and Alternating Current If one end of a magnet is plunged in and out of a coil of wire, the induced voltage alternates in directionThe frequency of the induced alternating voltage equals the frequency of the changing magnetic field within the loopGenerator – a machine that produces electric current by rotating a coil within a stationary magnetic fieldMost commercial generators are run by moving steam
8 TransformersWhen you have a pair of coils next to each other, you will have current passing through both when the power source is connectedWe refer to the coil connected to the power source as the primary (input) and the other as the secondary (output)The magnetic field builds up around the primary and extends into the secondaryWhen an iron core inside the coils, the magnetic field will be intensifiedTransformer – a device for increasing or decreasing voltage through electromagnetic inductionPrimary voltage/# of primary turns =secondary voltage/#secondary turnsPower into primary = power out of secondary(voltage x current) primary = (voltage x current) secondary
11 Induction of Electric and Magnetic Fields Faraday’s Law states:An electric field is created in any region of space in which a magnetic field is changing with time. The magnitude of the created electric field is proportional to the rate at which the magnetic field changes. The direction of the created electric field is at right angles to the changing magnetic field.The companion law is from James Maxwell, it states:A magnetic field is created in any region of space in which an electric field is changing with time. The magnitude of the created magnetic field is proportional to the rate at which the electric field changes. The direction of the created magnetic field is at right angles to the changing electric field.
12 Electromagnetic Waves An electromagnetic wave is composed of vibrating electric and magnetic fields that regenerate each otherThe vibrating fields emanate from the vibrating chargeAt any point on the wave, the electric field is perpendicular to the magnetic field, and both are perpendicular to the direction of motion of the waveElectromagnetic waves always move at the speed of light (3.0 x 108 m/s), no matter what the frequency or wavelength or intensity of radiation