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## Class 10 Physics (India)

### Course: Class 10 Physics (India)>Unit 4

Lesson 7: Electric generator & A.C.

# Alternating current, direct current & what is frequency?

Current that keeps changing is direction is called alternating current, (AC) whereas the one that never changes its direction is called direct current (DC). Power can be transmitted with low heating losses in the form of AC (not DC). The frequency of the AC in India is 50 Hz. This means the current changes it's direction 100 times per second. Created by Mahesh Shenoy.

## Want to join the conversation?

• What makes Coil to Rotate In a Generator ?
• We apply external force. I think it's usually a gasoline-driven turbine which rotates the coil.
Hope that helps. :)
• It’s very nicely explained. 🙂
• How does alternating current even work if it actually doesn't really move from its power plant? When alternating current starts being generated in a power plant, doesn't it go as long as it can in 1/100th of a second and then go back to where it started? Then, how does the electricity even come to our houses?
• I have learned the answer by now. There are already electrons moving very little distances in the wires, but that alternating current still generates electricity for our houses.
(1 vote)
• Can electrons in a circuit ever lose their charge? If they do, does that make A.C. less efficient?
• As explained in the video it says that the use of transformers can be done using AC only. Can we also give the reason that AC flows from above the wire?
• If we look at the last cycle i.e. the 50th one, the current will only change it's direction only once because the next cycle won't occur. Won't this mean that the current changes its direction 99 times?
(1 vote)
• Since the alternating current flows continuously, the current will never stop until the circuit is broken, so the current will change direction 100 times before the next set of 50 cycles. If I did not answer your question or if you are still confused, please let me know. :)
(1 vote)
• why cant we use DC with transformers ? we could send low electric energy through it too.
(1 vote)
• Why can't we supply DC with a low current and then connect it to the transformers for current supply?
(1 vote)
• Actually Transformers also work on elctromagnetic induction, There is a primary coil and secondary coil, alternating current reaches primary coil and generates changing magnetic field, this changing magnetic field again induces alternating current to secondary coil, remember that voltage coming through power lines is high but current is low. Therefore the power input to the primary coil is equal to the power output from the secondary coil. Power is equal to voltage multiplied by current (P = VI). So if the voltage is decreased by the transformer, the current must increase to maintain constant power. For eg let’s say we have a transformer with a primary voltage of 120V and a primary current of 2A. The power input to the primary coil is 120V * 2A = 240W. If the transformer steps down the voltage to 12V, the power output from the secondary coil must still be 240W. To maintain constant power, the secondary current must increase to 20A (240W / 12V = 20A).That's how a transformer increases the current.
I hope it clears your doubt, I don't know why video didn't explained working of transformers even though the concepts used in transformers is not beyond our syllabus but that is it.
(1 vote)