Electromagnetic Induction Chapter 37

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 coil The production of voltage depends only on the relative motion of the conductor with respect to the magnetic field The amount of voltage depends on how quickly the magnetic field lines are traversed by the wire Electromagnetic Induction – the phenomenon of inducing a voltage in a conductor by changing the magnetic field near the conductor

Electromagnetic Induction

Faraday’s Law The 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

Faraday’s Law

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 direction The frequency of the induced alternating voltage equals the frequency of the changing magnetic field within the loop Generator – a machine that produces electric current by rotating a coil within a stationary magnetic field Most commercial generators are run by moving steam

Generators and Alternating Current

Transformers When you have a pair of coils next to each other, you will have current passing through both when the power source is connected We 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 secondary When an iron core inside the coils, the magnetic field will be intensified Transformer – a device for increasing or decreasing voltage through electromagnetic induction Primary voltage/# of primary turns = secondary voltage/#secondary turns Power into primary = power out of secondary (voltage x current) primary = (voltage x current) secondary

Transformers

Power Transmission

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.

Electromagnetic Waves An electromagnetic wave is composed of vibrating electric and magnetic fields that regenerate each other The vibrating fields emanate from the vibrating charge At 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 wave Electromagnetic 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

Electromagnetic Waves

Homework Assignment Read Chapter 37 (pg. 577-591) Do Chapter 37 #23-42 (pg. 593-594) Do Appendix F, Chapter 37 #1-5 (pg. 691)