Asked by Helena

The electrical resistance of a wire waves directly as its length & inversely as the square of its diameter if a wire 30m long and 0.75mm in diameter has a resistance of 25ohms , find the length of a wire of the same material whose resistance is 30ohms whose diameter is 1.25mm respectively

Answers

Answered by Reiny
Even not remembering my physics, we can form the equation, since the relationship is given..

R = k L/d^2

25 = k(30)/.75^2
25 = k(30)(16/9)
k = 9(25)/((16)(30)) = 15/32

R = (15/32)L/d^2

plug in the 2nd set of numbers
30 = (15/32) L /1.25^2

finish it up by solving for L
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