Current intensity and the ammeter
Current intensity tells how much charge passes a point of the circuit each second. If a charge Q crosses any section of the wire during a time t, then I = Q ÷ t. Charge Q is measured in coulombs (C), time t in seconds (s), and current I in amperes (A), so 1 A = 1 C/s. A current is measured with an ammeter, which is always connected in series, so that all the current passes through it. A useful way to think of this: the number of people passing a door each minute. From the formula, Q = I × t and t = Q ÷ I. Careful with units: if the time is in minutes, change it to seconds first. Every calculation line should keep its units.
| Step | Value |
|---|---|
| charge | 90 C |
| time in seconds | 180 s |
| current | 0.5 A |
People at a door. A grown-up stands at a door and counts how many people pass in one minute while a friend times it. Calculate people per second as an analogy for I = Q ÷ t. Then draw a circuit with a cell, a lamp and an ammeter in series, and mark where the ammeter would be put. The ammeter must be in the line of the current, not across the lamp. Draw it only: no real meters are needed.