Lesson 9 of 11
The big picture
Show on a big screen| Idea | Rule |
|---|---|
| Charge on the move | I = Q ÷ t |
| Measuring a circuit | Ammeter in the path, voltmeter across a part |
| Ohm's law | V = IR, at a fixed temperature |
| Resistance depends on | Length, thickness, material: R = ρL ÷ A |
| Series and parallel | R = R₁+R₂+R₃, or 1÷R = 1÷R₁+1÷R₂+1÷R₃ |
| Heating effect | H = I²Rt |
| Power | P = VI = I²R = V² ÷ R |
| The meter | Energy = P × t. 1 unit = 1 kWh |
This chapter tells one story. Charge goes round the circuit and is not used up. Two meters read two different things. At one temperature, push and flow grow together in a straight line. A wire's shape and material decide its resistance. Two resistors give different totals joined two different ways. A current makes heat in a resistor. Power is the rate of using energy. The meter counts the energy used.
Chapter 11, Electricity, in your Science book covers these ideas. You already know them.