Thread: transformer

how is transformer step up or down the voltage?

Transformers work using electromagnetism. Whenever you run current through a conductor, like a piece of wire, an electromagnetic field is created around the wire. If you wind the piece of wire up in a coil, you pack all of the fields together and increase their density. If you wind that coil around a piece of iron...it further strengthens the electromagnetic field. That's how an electromagnet works.

Alternatively, if an electromagnetic field moves over a conductor (movement is essential) the EMF will induce or "create" a voltage within that conductor. This is how a radio antenae works. Radio waves made of EMF pass over the antenae and induce a small voltage in antenae, which is amplified.

A transformer uses both of these concepts. The primary coil turns the incoming current into EMF, and the secondary coil picks it up like an antenae. The number of turns in the coil on both sides determine if the voltage is stepped up or down. If you have 100 turns in the primary and 200 turns in the secondary, the voltage will be stepped up by 2 times....but the current will be reduced by half.


In this example, there are 14 turns of wire in the primary, and 7 on the secondary. That means the voltage will be stepped down by half...but the current will be increased by 2x.

We said in the other thread that Power= Current X Voltage. The power on both sides of the transform stays the same. You're just trading voltage for current, or current for voltage.

but how current increase while step up the voltage?

Originally Posted by sabari raja

but how current increase while step up the voltage?

You will have to formulate your question better. How does what current increase when you step up what voltage? In a step-up transformer the secondary current is less than the primary current.

It doesn't...it goes down. Essentially you're trading voltage for current, or current for voltage. If you step up the voltage, the current will decrease by the same factor. You can't make something from nothing. P=IV (I is the symbol for current) Power on both sides of the transformer have to be the same.

so the power is equal on both side

Yes, it's like gear ratios. You're trading off angular speed for torque, or vice versa.