%3Cp%3EA%20large%26nbsp%3Bspool%26nbsp%3Bin%26nbsp%3Ban%26nbsp%3Belectrician\'s%

Question

%3Cp%3EA%20large%26nbsp%3Bspool%26nbsp%3Bin%26nbsp%3Ban%26nbsp%3Belectrician's%26nbsp%3Bworkshop%26nbsp%3Bhas%26nbsp%3Bof%26nbsp%3B65%26nbsp%3Bm%26nbsp%3Bof%26nbsp%3Binsulation%26nbsp%3Bcoated%26nbsp%3Bwire%26nbsp%3Bcoiled%26nbsp%3Baround%26nbsp%3Bit.%26nbsp%3BWhen%26nbsp%3Bthe%26nbsp%3Belectrician%26nbsp%3Bconnects%26nbsp%3Ba%26nbsp%3Bbattery%26nbsp%3Bto%26nbsp%3Bthe%26nbsp%3Bends%26nbsp%3Bof%26nbsp%3Bthe%26nbsp%3Bspooled%26nbsp%3Bwire%2C%26nbsp%3Bthe%26nbsp%3Bresulting%26nbsp%3Bcurrent%26nbsp%3Bis%26nbsp%3B1.7%26nbsp%3BA.%26nbsp%3BSome%26nbsp%3Bweeks%26nbsp%3Blater%2C%26nbsp%3Bafter%26nbsp%3Bcutting%26nbsp%3Boff%26nbsp%3Bvarious%26nbsp%3Blengths%26nbsp%3Bof%26nbsp%3Bwire%26nbsp%3Bfor%26nbsp%3Buse%26nbsp%3Bin%26nbsp%3Brepairs%2C%26nbsp%3Bthe%26nbsp%3Belectrician%26nbsp%3Bfinds%26nbsp%3Bthat%26nbsp%3Bthe%26nbsp%3Bspooled%26nbsp%3Bwire%26nbsp%3Bcarries%26nbsp%3Ba%26nbsp%3B3.2-A%26nbsp%3Bcurrent%26nbsp%3Bwhen%26nbsp%3Bthe%26nbsp%3Bsame%26nbsp%3Bbattery%26nbsp%3Bis%26nbsp%3Bconnected%26nbsp%3Bto%26nbsp%3Bit.%26nbsp%3BWhat%26nbsp%3Bis%26nbsp%3Bthe%26nbsp%3Blength%26nbsp%3Bof%26nbsp%3Bwire%26nbsp%3Bremaining%26nbsp%3Bon%26nbsp%3Bthe%26nbsp%3Bspool%3F%3C%2Fp%3E

Explanation / Answer

V = I R

I = V/ R

R = ( rho) l / A

I1 = V / R1

I 1 = V A / (rho) l1

I2 = VA / ( rho ) l2

I1 / I2 = l2/l1

1.7 / 3.2 = x/65

x = 34.53125 metres

Length of remaining wire on spool = 34.53125 metres

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