a) Draw the circuit symbol for a resistor.

b) Draw the circuit symbol for a variable resistor.

a) Draw the circuit symbol for a thermistor.

b) Give one use for a thermistor.

c) Explain why a thermistor is suitable for this use.

What is the combined resistance of two $20 \mathrm{\Omega }$ resistors connected in series? 

Three resistors are connected in series with a battery, as shown.

Resistor A has the greatest resistance of the three. The current through A is $1.4 \mathrm{A}$ . What can you say about the currents through B and C?

What is the combined resistance of three $30 \mathrm{\Omega }$ resistors connected in series?

Use the idea of resistors in series to explain why a long wire has more resistance than a short wire (of the same thickness and material).

Use the idea of resistors in parallel to explain why a thick wire has less resistance than a thin wire (of the same length and material).