Lie Detectors are electronic circuits that are able to measure your skin’s resistance. When you sweat (or if your skin is wet), the resistance is different than if it’s dry.
However since most people don’t sweat when they lie, this type of detector isn’t the most reliable type of detector around, but it’s one of the simplest to create. We’re going to build one from simple electronic components like resistors, capacitors, and transistors.
Our lie detector uses a speaker that changes pitch depending on the resistance of your skin – it’s much more entertaining than blinking an LED on or off. You can think of this circuit as more of a skin humidity indicator. Are you ready?
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R1 does indeed affect the current. In the example, we determine the current across R1 first. Now that we know the resistance and current for R1, we can determine the voltage across R1.
Now that we know the voltage across R1, we can remove that amount of voltage from the rest of the circuit. Notice the equation V2 = V3 = Vtot – V1
The remaining voltage is 3.889V. Therefore R1 does affect the current and voltage across R2 and R3.
By the way, the current flowing through each resistor in a parallel circuit is different, depending on the resistance.
In a circuit with two resistors in parallel and one in series with that set, for example the circuit schematic in question 13, to find the current of one of the parallel resistors, e.g. R2, why do we use the resistance of that resistor alone? Doesn’t the resistor in series, R1, affect the current?