IGCSE PHYSICS Generators and Transformers By: Aseem Aggarwal

Induced Current in a Generator The effect of inducing a current in a coil by moving a magnet inside it is used for the generation of electricity in power plants. There are two types of generator or dynamo. Both turn rotational energy into electrical energy and produce alternating current: Involves rotating a coil inside a magnet Involves rotating a magnet inside a coil

Electrical Generator An electric generator consists of a magnet, which creates a magnetic field, and a loop of wire which rotates in the magnetic field. As the wire rotates in the magnetic field, the changing strength of the magnetic field through the wire produces a force which drives the electric charges around the wire. As the loop spins, the direction of the force and current changes. The changing direction of the force after every 180 degrees of rotation gives the alternating current.

Electrical Generator

Alternating Current If you use an oscilloscope and look at the power found at a normal outlet in your house, you will find is that the power looks like a sine wave, and that wave oscillates between -170 volts and 170 volts. The rate of oscillation for the sine wave is 60 cycles per second. Oscillating power like this is generally referred to as AC, or alternating current. AC has at least three advantages over DC in a power distribution grid: Large electrical generators happen to generate AC , so conversion to DC would involve an extra step. Transformers must have alternating current to operate, and the power distribution grid depends on transformers. It is easy to convert AC to DC but expensive to convert DC to AC, so if you were going to pick one or the other AC would be the better choice.

Three Phase Power The power plant produces three different phases of AC power simultaneously, and the three phases are offset 120 degrees from each other. If you were to look at the three phases on a graph, they would look like this relative to ground:

Transformer A transformer can change electrical energy of a given voltage into electrical energy at a different voltage level. It consists of two coils arranged in a way that the magnetic field surrounding one coil cuts through the other coil. When an alternating voltage is applied to one coil, the varying magnetic field set up around that coil induces an alternating voltage in the other coil. Transformers will not work with direct current, since no changing magnetic field is produced, and therefore no current can be induced.

Step Down Transformer This transformer's job is to reduce the 4160 volts down to the 240 volts that makes up normal household electrical service. It is a step down transformer.

Step Up Transformer (Power Plant)

Transformer The factor which determines whether a transformer is a step up (increasing the voltage) or step down (decreasing the voltage) type is the "turns" ratio. The turns ratio is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding.

Electromagnetic effects – Electromagnetic induction and a.c generator Damchuilung Kamei

Electromagnetic induction -Process in which a conductor cuts through a stationary magnetic field. -Causes production of a voltage across the conductor. -Voltage produced- induce EMF, causes induce current. - Creation of current in a wire: Wire moved through magnetic field. Magnetic field moved pass the wire. Magnetic field around the wire changes strength. Faster the changes, faster the current.

AC generator Dynamo AC Generator Simple current generator Magnet rotation of degrees causes the permanent magnet to reverse through the coil. Frequency of electricity depends on the bicycle. AC Generator Power stations use electro magnets instead of permanent magnets to create and pass magnetic fields. Generator- Mechanical to Electrical energy. Generator produces electromotive force.

transformer - Mutual induction- Two coils placed side by side, and current in one coil is switched on or off, voltage is induced in the other coil. - Size of voltage in the secondary coil depends on the ratio of turns wrapped around the sides of the iron core. - Formula-

bibliography texts pictures http://ap-physics.david-s.org/transformer/ http://ap-physics.david-s.org/a-c-generator/ http://ap-physics.david-s.org/electromagnetic-induction/ http://bit.ly/1Gpv6Xv http://bit.ly/1HIxN8e http://bit.ly/1GpvoxM http://bit.ly/1Ix91FJ