S4.12.1 For the adult
Charge and current
Amina presses the switch of a torch and the lamp lights at once. What is moving in the wires, and how can we count it?
What this chapter teaches
A current is a flow of charge. In a metal the moving charges are free electrons, started together by the cell, so a lamp lights at once. Charge in coulombs equals current in amps times time in seconds, Q = It. Current is not used up.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why does a lamp light at once when the electrons drift so slowly?
- A current of 2 A flows for 30 s. How much charge passes, and what is the working?
- Which way do the electrons go in a loop with a cell, and which way is the conventional current drawn?
After the chapter, the learner can
- Calculate charge from current and time
- Explain current in metals as a flow of electrons
What they copy into their notebook
Current is charge each second. I = Q ÷ t, so Q = It. Charge in C, current in A, time in s. Conventional current goes + to −. Electrons go − to +. Current is not used up.