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Electric Current


Electric current is the drift of electric charges. In electric wires, the charges are moved by free electrons whereas in electrolyte they are moved by the drift of ions. There can even be the drift of positive ions in one direction and negative ions in the opposite direction at the same time. Lets see more about it.

Electric Current Definition

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The electric current is defined as the charge flow rate that is the charge flowing per second through any cross-sectional area is called electric current, denoted by I. If charge q flows through any cross-section in time t, then electric current formula is given as
I = $\frac{q}{t}$
I is the electric current,
q is electric charge and
t is time taken.

Electric Current Formula

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There are three electric current formulas
I = $\frac{q}{t}$
q = charge
t = time taken.

I = $\frac{dq}{dt}$
dq = small change in Charge
dt = Small change in time

I = $\frac{V}{R}$
V = Voltage applied to the conductor
R = Resistance of the conductor

Electric Current Unit

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The electric current unit in SI system is coulomb/second or ampere and its symbol is Amperes or ‘A’. The charge is expressed in Coulomb and time in seconds. If q = 1 coulomb and t = 1 second, then electric current I is given as
I = $\frac{q}{t}$ = 1 coulomb/second = 1 Ampere

i.e., 1 ampere current is the current produced in a conductor when one coulomb of charge flows through its cross-section in one second.

As 1 coulomb charge is equivalent to 6.25 x 1018 electrons or elementary charges, thus 1 ampere current in a conductor means the flow of 6.25 x 1018 electrons per second through the cross-section of the conductor.Thus, 1A = 1 coulomb/second = 6.25 x 1018 electrons/second. Clearly for 2A current, a charge of 2 coulomb must flow in one second.

Alternating Current

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If the current direction changes after equal intervals of time, it is called alternating current. It can be written as AC or ac. Most of the power stations generate alternating current. The ac waveform is given as,
AC Waveform
The ac source current is given as,
AC Source
Hence, iIf the electric current is of 100 Hz then it tells that the current changes its direction 60 times per second.

Direct Current

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If the flow of electric current flow is in the same direction, its referred as Direct current. It is symbolized as DC or dc. The battery current is direct current as it is in one direction. Here the terminals both positive and negative are fixed. Its dc wave form is,
DC Waveform
It is symbolized as,
DC Source

Conventional electric Current

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In convection, heat is transferred from one place to the other by the actual motion of the heated particle of the medium. For example, in hot air blower, air is heated by a heating element and the heated air is blown by a fan. the air carries the heat wherever it goes. Thus,

Convection is a process of transfer of heat by the actual movement of the medium particles.Liquids and gases are the bad conductor of heat. They are heated mainly by the process of convection. In a solid, the atoms cannot move, leaving their positions. So solids are not heated by canvection.A medium is required for the transfer of heat by convection.

By the process of convection, the transfer of heat is always vertically upwards.The reason is that the medium particles near the source oh heat absorb heat from the source and they start moving faster. As a result the medium at this place becomes less dense so it rises up and the medium from above being denser, moves down to takes its place. Thus a current is set up in the medium which is called a convection current. The current continues till the entire medium acquires the same temperature.

Examples of Electric Current

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Lets see some examples of electric current:

Solved Examples

Question 1: The current of 15 Amperes flows through a conductor for 5 minutes. Find the charge flowing in it?
The charge is given by q = I × t
where, I = Current = 15 A and t = time = 5 min

Charge, q = 15 A × 5 × 60 sec
            q = 4500 coulombs.
So, the Charge flowing through the conductor is 4500 coulombs.

Question 2: A voltage of 5V flows through 3 $\Omega$ resistor. Calculate the current flow.
Voltage V = 5v, resistance R = 3 $\Omega$

Current, I = $\frac{V}{R}$
             = $\frac{5}{3}$
             = 1.7 A.