Everything Science Grade 11

19.5 CHAPTER 19. ELECTRIC CIRCUITS

the midpoints. In orderto determine the unknown resistance, R 2 is varied until this condition is
reached. That is when the voltmeter reads 0 V.

Example 8: Wheatstone bridge

QUESTION

What is the resistance of the unknown resistor Rxin the diagram below if R 1 =4Ω R 2 =8Ω

and R 3 =6Ω.

R 3 R 1

R 2 Rx

V

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A

B

C

D Circuit for Wheatstone bridge

SOLUTION

Step 1 : Determine how to approach the problem

The arrangement is a Wheatstone bridge. So weuse the equation:

Rx: R 3 = R 2 : R 1

Step 2 : Solve the problem

Rx: R 3 = R 2 : R 1

Rx: 6 = 8 : 4

Rx = 12 Ω

Step 3 : Write the final answer

The resistance of the unknown resistor is 12 Ω.

Extension: Power in electric circuits