# Alternating current : defination, explanation, invention

## Alternating current

The magnitude of current is changes continuously and its direction reverse in every half cycle is know as alternating current (AC).
Its main application is used for long transmission of current.
Here we also discuss why bulb 💡 is not on off during application of alternating current. So many interesting topic will discuss here.
So for interesting application check out the last section heading as important notes about alternating current. So let's started 👍🎓.

### Invention of alternating current

At earlier stage, alternating current is produced by dynamo electric current generator, which was constructed by Hippolyte pixii in 1832.The device dynamo working on the principle of Michael Faraday's law.
Alternating current was came into practice application by Guillaume duchenne, inventor and developer of electrotherapy. And further alternating current was developed by Hungarian Ganz works company in 1870s. In this way it was developed with time.

## Alternating emf

We know that, when a coil is rotate in a uniform magnetic field an emf is induced in the coil. Variation of emf with time,
E= Eo+sin(wt)

E= instantaneous emf
Eo= maximum value of emf
w = angular momentum
t= time

The emf has following characteristics :
1. It varies continuously with time. As it clear from fig. that no consecutive instant of time have same value of emf.
2. It varies periodically with directions. The direction of emf during the time interval OB and that during the interval BD are opposite to each other. This phenomenon gets repeated after equal interval of time. Such an emf is known as alternating emf.
An alternating emf one which continuously changes in magnitude and periodically reverse in direction.
Graphically it is represented by sinusoidal curve whose mathematical form is given in the above equation.

### Alternating current

If external circuit is closed, the alternating emf produced in the coil rotating in a uniform magnetic field will cause a current to flow. This current is know as alternating current.
This is also possesses same properties which is accure by alternating emf.
Mathematically alternating current is represented as
I=Io sin(wt)
I= instantaneous current
Io= maximum current

#### Some term related to alternating current

1. Peak value(Io)
It is the maximum value of electric current in either direction.
It has constant magnitude which depends upon the alternating emf and the net opposition offered by the circuit.

2. Time period
It is the time interval after which the instantaneous current in the circuit will repeat both in case of direction and magnitude.

3. Cycle of alternating current
Variation of current in between two consecutive, similar values of current is said to constitute one cycle AC.

4. Frequency
Number of alternating current cycle complete  in one second is known as frequency of alternating current.
Frequency is denoted by f.
Low frequency such as 50 and 60 cycle per second, are used for domestic and commercial power. But alternating current of frequency around 100,000,000 cycle per second (100 megahertz) are used in television.

5. Phase
There is always a generating element rotating in uniform magnetic field for purpose of AC.
Phase of alternating current is measured by angle (wt) turned by the generating element with respect to certain instant of time.

6. Phase lag between emf and current
Common sense tell us that electric current in the circuit should be maximum when emf in it is maximum. This may not be used in an AC circuit.
Wheather this is true or not, it depends upon the nature of circuit element contained in circuit.
Generally, emf E and current i  have a phase difference between them.
1. When phase difference is equal to zero, E and i are said to be in phase with each other.
2. When phase difference is negative, emf leads the current.
3. When phase difference is positive, emf lags behind the electric current.

#### Important notes on alternating current

1. Greater the frequency of alternating current smaller will be the duration of cycle of AC. As a result the consecutive maximum will be situated close to each other.
2. During one cycle current becomes zero twice. Thus, an electric bulb, fed with AC, shall put off twice in one cycle. But this is not visually observed. This is due to property of persistence of vision.
The time interval between two consecutive brightness is much less than 1/16th of a second. Therefore, the two consecutive impression of brightness merge into one another, thus, alternating the region of darkness.
3. Alternating current is dangerous to human life. This is due to high frequency (50c/s) of AC .When a person ,having communication with ground, touches a live wire, 50c/s AC passes through his body.
All parts of his body including his brain, start vibrating with a frequency of 50c/s . Therefore, his brain is rendered helpless to reply orders to his different part of body, with the result that body remains paralysed in same position. If the live wire is not remove away, within a seconds , it may prove fatal. It should be kept in mind that the wire should be removed away only with an insulating material.

This is all about alternating current. If you have any queries you can ask in comment box.
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