question_answer 6)

A copper wire has a diameter of 0.5 mm and a resistivity of 1.6 × 10?6 . How much of this wire would be required to make a 10  coil? How much does the resistance change if the diameter is doubled?

Answer:

We are given that, diameter of the wire, D = 0.5 mm = 0.5 × 10?3 m resistivity of copper,   = 1.6 × 10?6 ohm cm = 1.6 × 10?8 ohm m required resistance, R = 10 ohm As  R = ,  =   [A =  = ] or                         m = 112.7 m Since,  R = , R  1/D2. When D is doubled, R becomes  times.