1. An interesting electrical circuit:
Have a look at the circuit diagram below.
When the switch is open, as shown in the diagram, both bulbs are lit. But when the switch is closed, bulb A becomes brighter, but bulb B goes out.
When the switch is open, how is electricity flowing round the circuit?
When the switch is closed, what must happen to the current through bulb B?
Which must have the greatest resistance - the part of the circuit with bulb B in it, or the loop with the switch in it? Explain your answer.
Can you explain why bulb B goes out when the switch closes? A B

2. Answers
Electricity just flows around the first loop of the circuit, through both bulbs.
Bulb B goes out, so the current must have decreased a lot.
It must be the part of the circuit with bulb B in it because the current must now be flowing through the switch, which must have a lower resistance.
The part of the circuit with the switch has a lower resistance than the part with bulb B. When the switch closes, the charges flow through it rather than bulb B. As a result, bulb B goes out. A B