Electric current (B): cells, resistance and symbols
Answers are for parents and teachers.
1
Six cells of 1.5 V are joined in series. Find the emf. What if they are joined in parallel?
Series: 6 × 1.5 V = 9 V. Parallel: 1.5 V.
2
How many 2 V cells in series give 12 V?
12 V ÷ 2 V = 6 cells.
3
Explain how a rheostat dims a lamp, in two sentences.
Sliding the contact puts more wire in the circuit, so the resistance goes up. The current falls and the lamp dims.
4
A 3 m wire has 9 Ω. What is the resistance of 2 m of the same wire?
9 Ω ÷ 3 m = 3 Ω per metre, so 2 m × 3 Ω/m = 6 Ω.
5
Draw the symbols of a cell, a bulb, a closed switch and an ammeter.
Check against the picture: a cell (long and short lines), a bulb (circle with a cross), a closed switch (a line joining two dots), an ammeter (circle with A).