What Is Electric Current?
The flow of electric charge through a conductor, measured in amperes (A). It represents how many charges pass a point in a circuit per second.
Think of electricity like water flowing through a pipe. The current is like the flow rate of the water — how much water passes a certain point every second. In a circuit, instead of water molecules, we have electrons moving through a wire.
There are two ways to describe the direction of current flow:
- Conventional current flows from the positive terminal to the negative terminal of a battery through the external circuit (this is the standard we use in circuit diagrams).
- Electron flow is actually in the opposite direction — electrons move from negative to positive through the external circuit.
In MYP Sciences, we always use conventional current direction (positive to negative through the external circuit) unless told otherwise. This is a historical convention established before scientists discovered that electrons carry charge.
Current is measured using an ammeter, which must always be connected in series with the component you are measuring.
Imagine a queue of people walking through a turnstile. The number of people passing through per minute is like the current — higher current means more charge flowing every second.
Measuring Current: The Ampere
The SI unit of electric current. One ampere equals one coulomb of charge passing a point per second:
The relationship between current, charge, and time is given by:
Where:
- = current in amperes (A)
- = charge in coulombs (C)
- = time in seconds (s)
Example: A charge of 30 C flows through a wire in 6 seconds. What is the current?
Step 1: Identify the known values: ,
Step 2: Apply the formula:
Answer: The current is 5 A.
In everyday devices, you'll often encounter smaller units:
- Milliampere (mA): 1 mA = 0.001 A (used for small electronics like phones and LEDs)
- Microampere (μA): 1 μA = 0.000001 A (used in sensors)
To convert mA to A, divide by 1000. For example, 250 mA = 0.25 A. Always convert to base units before substituting into formulas!
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