### Current

- An electric current I is a measure of the rate of flow of electric charge Q through a given cross-section of a conductor.
- In other words, current is the measure of how fast the charge flow through a cross section of a conductor.

**Equation**

$$Current=\frac{\text{TheAmountofChargeFlow}}{\text{TimeTaken}}$$ or

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

### Direction of Current

- Conventionally, the direction of the electric current is taken to be the flow of positive charge.
- The electron flow is in the opposite direction to that of the conventional current.
- In a circuit, current flow from the positive terminal to the negative terminal.
- In a circuit, electrons flow from the negative terminal to the positive terminal.

### Unit of Current

- The SI unit for current is the ampere (A).
- The current at a point is 1 ampere if 1 Coulomb of electric charge flows through that point in 1 second. Therefore, 1 A = 1C/s.

**Example 1**:

If 30 C of electric charge flows past a point in a wire in 2 minutes, what is the current in the wire?

**Answer**:

Charge flow, Q = 30C

Time taken, t = 2 minutes = 120s

Current,

$$\begin{array}{l}I=\frac{Q}{t}\\ I=\frac{30}{120}=0.25A\end{array}$$

**Example 2**:

Current of 0.5A flowed through a bulb. How many electrons had flowed through the bulb in 5 minute? (The charge of 1 electron is equal to -1.6×10

^{-19}C)

**Answer**:

Current, I = 0.5A

Time taken, t = 5 minutes = 300s

$$\begin{array}{l}I=\frac{Q}{t}\\ Q=It\\ Q=(0.5)(300)=150C\end{array}$$ Charge of 1 electron, e = -1.6×10

^{-19}C

Number of electrons, n = ?

$$\begin{array}{l}Q=ne\\ n=\frac{Q}{e}\\ n=\frac{150}{1.6\times {10}^{-19}}=9.375\times {10}^{20}\end{array}$$