Inverse Proportion

Question

The resistance R of a wire of a constant length is inversely proportional to the square of its diameter d.  If the resistance of a wire 2 mm in diameter is 25 ohms, find

 
a) an equation connecting the resistance of the wire, R, to the diameter of the wire,d.

b) the resistance of a wire with diameter 2.5 mm

c) the diameter of a wire with a resistance of 15 ohms.

Answer 1

1.   R=100/diameter^2.....d in mm

2. if d=2.5, R=100/2.5^2=100/6.25=16

3. R=15=100/d^2, so d^2=100/15=6.666666666

d=2.5819888987