4.2.2 Electric Current
What is Electric Current?
Electric current is the flow of electric charge through a conductor. Think of it like a stream of water flowing through a pipe. 💧
Mathematical Definition
The current \$I\$ is defined as the amount of charge \$Q\$ that passes a point in a circuit per unit time \$t\$:
| Symbol | Meaning |
|---|
| \$I\$ | Electric current (ampere, A) |
| \$Q\$ | Charge (coulomb, C) |
| \$t\$ | Time (second, s) |
\$I = \dfrac{Q}{t}\$
Units and Conversion
- 1 ampere (A) = 1 coulomb per second (C / s)
- ⚡ Example: If 5 C of charge passes a point in 10 s, the current is \$I = 5/10 = 0.5\$ A.
Analogies to Help You Remember
- 💧 Water Flow: Charge is like water, the conductor is the pipe, and current is the rate of water flow.
- 🚗 Traffic: Cars (charges) move along a road (conductor). Current is the number of cars passing a point per second.
- 📦 Package Delivery: Packages (charges) delivered through a conveyor belt (conductor). Current is the rate of package delivery.
Quick Practice
Calculate the current if 12 C of charge passes a point in 3 s.
Solution: \$I = \dfrac{12}{3} = 4\$ A. ⚡
Key Takeaways
- Current is a rate: charge per unit time.
- Equation: \$I = Q/t\$.
- Units: ampere (A) = coulomb per second (C / s).
- Use analogies to visualize flow.