Electromagnetic Induction

When a magnet and a wire move relative to each other, a voltage is induced Amount of voltage produced depends on: –Speed: High speeds produce high voltages –Magnetism: Strong magnets produce high voltages –Shape of Wire: Many coils in the wire produce high voltages

Electromagnetic Induction

Note: It is more difficult to push the magnet into a coil with more loops because the high current generates a stronger magnetic field which acts against the magnet.

Electromagnetic Induction Electromagnetic Induction: Inducing voltage by changing the magnetic field around a conductor –ANY change in magnetic field will induce a voltage –i.e.) Traffic control signals

Faraday’s Law The induced voltage in a coil is proportional to the number of loops multiplied by the magnetic field changes within those loops.

Faraday’s Law When a magnet moves past different materials, the voltage induced is the same for each case The most current will be produced in the material where the electrons are bound most loosely –i.e.) The magnet will produce a larger current when moving past copper than rubber

Bell Ringer To produce a current in a coil of wire with a magnet, what must occur? What type of current will this produce?

Generators and AC As a wire moves back and forth past a magnet, the resulting current changes direction (AC) Recall: A motor converts electrical energy (from the battery) into mechanical energy (rotation of the armature) A generator converts mechanical energy into electrical energy

Generators and AC

Turbine: When the armature of a generator is connected to a wheel which captures wind, water, or steam in order to turn and produce electrical energy

Bell Ringer Explain what the difference is between a generator and a motor in terms of energy.

Transformers Consider two coils side by side: –Primary Coil: Connected to a voltage source –Secondary Coil: Connected to a galvanometer

Transformers When the voltage source is turned on: –Current briefly surges through the secondary coil When the voltage source is turned off: –Current briefly surges through the secondary coil in the opposite direction The magnetic field building around the primary extends to the secondary –Changes in magnetic field intensity induce voltage in the secondary

Transformers Placing a core within the coils will intensify the magnetic field The secondary will intercept more of the field change

Transformers Instead of switching a DC voltage source off and on, the device is connected to an AC voltage source The rate at which the magnetic field changes = frequency of the AC current This device is known as a transformer

Transformers Used to step voltages up or down –i.e. Used in AC adaptors

Transformers Voltage is stepped up: –When the number of coils (turns) in the secondary > number of turns in primary Voltage is stepped down: –When the number of coils (turns) in the secondary < number of turns in primary Since voltages can be stepped up and down so easily, electrical power is primarily in the form of AC

Induction of Electric and Magnetic Fields According to Faraday: –Electric fields are created in any region of space where a magnetic field is changing with time. According to Maxwell: –A magnetic field is created in any region of space where an electric field is changing with time. These laws are inverses of each other and lead to the concept of electromagnetic waves

Electromagnetic Waves Composed of vibrating electric and magnetic fields the regenerate each other –Waves move outward from a vibrating charge –E.F. is always perpendicular to the M.F. and both are perpendicular to the direction of the moving wave

Electromagnetic Waves

All electromagnetic waves move at the speed of light –Discovered by Maxwell Changing electric fields constantly induce changing magnetic fields and vice versa –If the waves traveled at less than the speed of light, they would rapidly die out

Electromagnetic Waves Maxwell found that light is simply an electromagnetic wave vibrating at a specific frequency 4.3 x to 7 x vibrations per second This frequency stimulates the retinas in our eyes and allows us to see these waves