ch37_ccjp

=Chapter 37=

Electromagnetic Induction
An electric current can be created by moving a magnet through a wire coil because voltage is induced by the motion between the wire and the magnetic field. The amount of voltage induced depends on how fast the magnetic field lines are transversed by the wire. The greater number of loops a wire has, the greater the induced voltage and the greater the current. The force that is placed on the magnet times the distance the magnet is moved equals input work. Electromagnetic induction: phenomenon of inducing voltage in a conductor by changing the magnetic field near the conductor.

Faraday's Law
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.

Generators and Alternating Currents
As the magnetic field strength inside the coil is increased, the induced voltage in the coil is directed in one way. Generator: rotating coil in a stationary magnetic field, converts mechanical energy to electric energy. Motor: transforms electric energy into mechanical energy. As the loop in the generator rotates, there is a change in the amount of magnetic field lines. Voltage induced by a generator alternates and the current that is produced is an alternating current (ac). To define the current, it is the number of cycles or changes per second (Hz). Turbine: made up of coils wrapped around an iron core to make an armature. The armature is connected to an assembly of paddle wheels. Electricity is a form of energy, not a source of energy.

Motor and Generator Comparison
The motor effect is when a current moves to the right so that there is an upward perpendicular force on the electrons. The generator effect is when a wire of no current is moved down so that the electrons experience a deflecting force perpendicular to the motion creating a current.

Transformers
Primary/input is the coil connected to the power source. Secondary/output is the coil not connected to the power source. If a current flows through the primary, then a current also occurs in the secondary, but in the opposite direction. If an iron core is placed into the coils, the magnetic field is concentrated in the core, which also concentrates the magnetic field in the secondary. Transformer: a device for increasing or decreasing voltage through electromagnetic induction. Voltages can be increased or decreased with transformers depending on how many loops are in the secondary. Step-up transformer has more loops on the secondary. Also induces more voltage. Step-down has more loops on the primary. Primary voltage over the number of primary turns equals the secondary voltage over the number of secondary turns. Power into primary equals the power out of secondary. Electric power equals the voltage times the current of the primary equals the voltage time the current of the secondary.

Power Transmissions
Energy is transformed by one system of conducting wires to electromagnetic induction. Power is transmitted great distances at high voltage and transformers are used to help lower the voltage in order to have usable electricity in everyday life.

Induction of Electric and Magnetic Fields
Faraday's law An electric field is created in any space in which the magnetic field is changing with time. Magnitude of an electric field is proportional to the rate at which the magnetic field changes. The direction of hte created electric field is perpendicular to the changing magnetic field.

Maxwell's companion to Faraday's Law Magnetic field is created in any space where an electric field is changing with time. The magnitude of is proportional to the rate at which electric field changes. The direction of the magnetic field is perpendicular to the changing electricc field.

Electromagnetic Waves
A magnetic field will create a changing electric field and the electric field will create a changing magnetic field. An electromagnetic wave is composed of vibrating electric and magnetic fields that regenerate each other; no medium is neccessary. The vibrating fields move outwards from the source. The electric field is perpendicular to the magnetic field. Perfect balance is necessary between a magnetic field and an electric field in order for them to coexist. The changing electiric field induces the magnetic field and the changing magnetic field acts back to induce the electric field; only one speed can preserve this balance. The critical speed is 300,000 km/s. The radiation of any frequency propagates at the speed of light.