Electromagnetic Induction Electromagnetic Induction When a magnet and

Electromagnetic Induction

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

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

Generators and AC

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

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 1014 to 7 x 1014 vibrations per second • This frequency stimulates the retinas in our eyes and allows us to see these waves