Current Electricity
1.0 Introduction
1.0 Introduction
The study of electric charge in motion is known as current electricity.
Electric Current
The rate of flow of charge through any cross-section of wire is known as electric current.
If a charge $\Delta Q$ passes through any cross-sectional area in time $t$ to $t + \Delta t$ , then current $I$ at time $t$ is
$${I = \mathop {\lim }\limits_{\Delta Q \to 0} \frac{{\Delta Q}}{{\Delta t}} = \frac{{dQ}}{{dt}}}$$
In case of steady current i.e rate of flow of charge($Q$) does not change with time(t),then
$$I = \frac{{{\text{Total charge}}}}{{{\text{Total time}}}} = \frac{Q}{t}$$
SI unit of current is Ampere $(A)$.
One Ampere $(1A)$= $\frac{1C}{S}$
If one coulomb of charge flows through any cross-sectional area in one second, then the current through that area is $1A$.
Smaller current are expressed in following unit,
- 1milliampere$=1mA{10^{ - 3}}A$
- 1microampere$=\mu $A=${10^{ - 6}}A$
The conventional direction of electric current is the direction of motion of positive charges.
Electric current is a scalar quantity.
Although electric current has both direction and magnitude, it does not obey vector law of addition. So, it is a scalar quantity and not a vector quantity.
In the figure, wire $OA$ and $OB$ has current ${I_1}$ and ${I_2}$ respectively and current in wire $OC$ is scalar addition of ${I_1}$ and ${I_2}$ i.e
$${I = {I_1} + {I_2}}$$
Current through a conductor of non-uniform cross-section
Current will be same for all cross-sections of a non-uniform conductor. As shown in figure below ${I_1} = {I_2} = {I_3}$.
Types of current
| S. No. | Direct current (DC) | Alternating current (AC) |
| (a) | Unidirectional flow of electric charges. | Flow of electric charge periodically reverses direction. |
| (b) |  |  |
| (c) | Shows heating effect of current | Shows heating effect, chemical effect and magnetic effect of current. |
Current carriers
The charged particles flowing in a definite direction which constitutes an electric current is known as current carriers.
Different types of current carrier are:
- Solids: In a metallic conductor, electrons are the current carriers.
- Liquids: In electrolytic liquids, positively and negatively charged ions are current carriers.
- Gases: In ionized gases, positive and negative ions are the current carriers.
- Semiconductor: In semiconductor, holes and free electrons are current carriers.
