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A Wheatstone bridge is balanced. The carbon resistor in the R1 arm carries the colour bands Orange, Red, Brown. The other arms are R2 = 80 ohm and R4 = 40 ohm. Taking the colour-code values as exact, what is the colour code of the carbon resistor required in arm R3?

1. Red, Green, Brown
2. Brown, Blue, Brown
3. Grey, Black, Brown
4. Brown, Blue, Black

Correct answer: Brown, Blue, Brown

Solution

R1 = (Orange,Red,Brown) = 32 x 10 = 320 ohm. Balance gives R3 = R1*R4/R2 = 320*40/80 = 160 ohm = (Brown,Blue,Brown).

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