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What is alternating current?

What is Alternating Current?&How it works in electric appliances?why don’t we use Direct Current for every appliance?
Asked Prashant Benjamin
Answer:
Alternating current is defined as the current which changes its direction and magnitude periodically with time.
Alternating current is cheaper to produce and transmit.
The electric appliances depend on one or more of the effects of current like heating effect, chemical effect, magnetic effect etc.
Except where there it requires a unidirectional flow of charges,like chemical effects or electronic devices,  we may use either ac or dc.
In appliances utilizing direction independent effects of current, like heatinf effect, we may use ac or dc.

How is ultrasound used in medical field?

How is ultrasound used in medical field?

Asked Divyashree

Answer

Ultrasound are produced by vibrations of frequency more than 20000 Hz. Theya re not heard by us. Ultrasound has got plenty of applications in different fields. The main applications in medical field are:

1. Ultrasonography

http://en.wikipedia.org/wiki/Medical_ultrasonography

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