Question

A large spool in an electrician's workshop has 67 m of insulation-coated wire coiled around it. When the electrician connects a battery to the ends of the spooled wire, the resulting current is 2.3 A. Some weeks later, after cutting off various lengths of wire for use in repairs, the electrician finds that the spooled wire carries a 2.8-A current when the same battery is connected to it. What is the length of wire remaining on the spool?

Answer 1

    …(1)

The initial length of wire

Let its resistance

Let the emf of battery

Let the current through the wire

…(2)

Let the length of wire remaining  

Let the resistance for this wire

Current through the wire

   

      …(3)

From (2) and (3),

    …(from 1)