Class 10 > Unit # 15: Current Electricity > Electric Current

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Electric Current: Electronic, Conventional, AC, and DC

Q.1 Define Electric Current. Differentiate between (i) Electronic and Conventional Current (ii) Alternating Current and Direct Current.

Electric Current

"The rate of motion of charges in a conductor is called electric current. The strength of current in a conductor can be defined as the number of coulombs of charge which pass any cross-sectional area of the conductor in one second."

If a charge of $Q$ coulombs flows through a section of a conductor in $t$ seconds, the electric current $I$ is given mathematically by:

$I = \frac{Q}{t}$

Since total charge quantization is expressed as $Q = ne$ (where $n$ is the number of electrons and $e$ is the electronic charge), current can also be written as:

$I = \frac{ne}{t}$

Units of Current

The SI unit of electric current is the Ampere ($\text{A}$). Its sub-multiples are commonly used in electronics:

• $1\text{ milliampere } (1\text{ mA}) = 10^{-3}\text{ A}$
• $1\text{ microampere } (1\text{ }\mu\text{A}) = 10^{-6}\text{ A}$

(i) Difference Between Electronic Current and Conventional Current

Electronic Current	Conventional Current
1. Flow of current is from the negative terminal to the positive terminal of the battery.	1. Flow of current is assumed to be from the positive terminal to the negative terminal of the battery.
2. Represents the actual physical movement of free electrons.	2. Represents the historical convention of positive charge flow (used in circuit analysis).

Fig: Directional difference between conventional current (+ to -) and electronic current (- to +).

(i) Difference Between Alternating Current (AC) and Direct Current (DC)

Alternating Current (AC)	Direct Current (DC)
1. The current that periodically reverses its direction of flow at regular intervals.	1. The current that always flows in one constant direction.
2. Almost all power stations in Pakistan generate AC with a standard frequency of $50\text{ Hz}$.	2. Typically obtained from electrochemical cells and batteries (e.g., cell phone batteries, lead-acid accumulators).
3. Can be easily stepped up/down using transformers and transmitted over very long distances efficiently.	3. Cannot be transmitted over long distances efficiently due to significant resistive power losses.

Fig: Graphical representation of Alternating Current (reversing wave) vs. Direct Current (constant flow).

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