A) Calculate the cross-sectional area, in mm², of a piece of copper wire, 40 m in length
and having a resistance of 0.25 2. Take the resistivity of copper as 0.02 x 10-6 22 m.
b) A coil of 20 2 resistance is joined in parallel with a coil of R2 resistance. This
combination is then joined in series with a piece of apparatus A, and the whole circuit
connected to 100 V mains. What must be the value of R so that A shall dissipate 600
W with 10 A passing through it?
c) A load taking 200 A is supplied by copper and aluminium cables connected in parallel.
The total length of conductor in each cable is 200 m, and each conductor has a cross-
sectional area of 40 mm2. Calculate:
the voltage drop in the combined cables;
the current carried by each cable; .
the power wasted in each cable. Take the resistivity of copper and aluminium
as 0.018 um and 0.028 um respectively.