TRANSFORMER

Devices that increase or decrease the voltage of alternating current. Consists of 2 coils wrapped around an iron core. The two coils are insulated in such a way that no current can flow from one coil to the other. AC current passes through first coil, inducing a current in second wire. The phenomenon of changing the current in a coil to induce a voltage and a current in another coil is called mutual induction..



Types of Transformers

Step-up transformers (Increases Voltage)


Is a transformer which has the output voltage greater than the input voltage due to Ns > Np.


Step-down transformers (Decreases Voltage)


Is a transformer which has the output voltage smaller than the input voltage due to Ns < Np.


How to build a simple transformer??


In figure above, the primary coil is connected to an a.c. power supply and the secondary coil is connected to a load such as a light bulb.

ELECTROMAGNETIC INDUCTION

An electromotive force (e.m.f.) will be induced in a conductor when the conductor moves through a magnetic field. This effect is called electromagnetic induction. According to Faraday,s Law, the size of the induced e.m.f. is proportional to the rate of change of the magnetic field. Reversing the direction of movement of the conductor will cause the induced e.m.f. to produce a current in the opposite direction. The direction of induced current can be determined by using the Fleming’s Right Hand Rule.



Induced current in a solenoid…

When a magnet bar is thrust into a coil connected to an electric circuit, it causes a current to flow in the circuit to which the coil is attached.





When the magnet is withdrawn, the direction of current is reversed..



Lenz’s Law states that the induced current always acts to oppose the action producing it.