## Question

Two resistors R_{1} and R_{2} are connected up in a circuit as shown in the figure below.

When the switch S is open, the ammeter reads 1.0 A and the voltmeter reads 8.0 V.

When the switch S is closed, the ammeter reads 1.5 A and the voltmeter reads 6.0 V.

Determine the values of R_{1} and R_{2}. Show your working clearly.

## Answer

When the switch S is open, the current only flows through R_{2}.

The circuit can be simplified as shown:

We can calculate the value of R_{2} directly.

When the switch S is closed, the current flows through both R_{1} and R_{2}.

We can calculate the resistance across XY:

Since R_{1} and R_{2} are connected in parallel and we know the resistance across XY,

Hence, R_{1} is 8.0 Ω and R_{2} is 8.0 Ω