Question

Draw an electrical circuit for the Pee Checker 9000. We want the “Stop drinking” LED to light up when the conductivity of the urine is 0.1 S m-1 or less.

In your junk pile you have:

1. Knowledge of the Wheatstone bridge and how you can use it to measure an unknown resistance.

2. All the resistors you could possibly need.

3. No voltmeters or ammeters (including them would make the Pee Checker too expensive).

4. An LED that we’ll assume draws no current but lights up if more than 1 V is applied across it. The symbol for an LED is shown here

5. A battery that provides 3 V.

Answer 1

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