Electric current is the flow of electric charge. Think of it like a stream of tiny water droplets (electrons) moving through a pipe (wire). The amount of charge that passes a point in one second is called the current, measured in amperes (A).
Mathematically,
\$I = \frac{Q}{t}\$
where I is current, Q is charge, and t is time.
In d.c. the electrons move in one direction only, just like a one‑way street.
- The voltage stays constant or changes very slowly.
- Used in batteries, flashlights, and most small electronic devices.
- Example: A 9 V battery powers a toy car. The electrons flow from the negative to the positive terminal, always in the same direction.
In a.c. the electrons change direction periodically, like a pendulum swinging back and forth.
- The voltage oscillates sinusoidally:
\$V(t) = V_0 \sin(\omega t)\$
where V₀ is the peak voltage and ω is the angular frequency.
- Used in household mains supply (230 V in most countries) and in power plants.
- Example: The electricity that powers your TV and lights flows back and forth many times per second (50 or 60 Hz).
| Feature | Direct Current (d.c.) | Alternating Current (a.c.) |
|---|---|---|
| Direction of flow | One way | Reverses periodically |
| Typical source | Batteries, solar cells | Power plants, mains supply |
| Voltage behaviour | Constant or slowly varying | Oscillates sinusoidally |
| Common use | Portable electronics | Household appliances, long‑distance transmission |