a) What does LDR stands for?

b) Draw its circuit symbol.

c) What happens to the resistance of an LDR when light is shone on it?

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.

Redraw the circuit shown below by including a light-dependent resistor in place of the thermistor.

 Explain why the bell would be silent when the LDR is in darkness.

Explain why the bell would ring when light shines on the LDR.

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?

Two resistors are to be connected to form a potential-divider circuit. Should they be connected in series or in parallel with each other?