Ten identical cells connected in series are needed to heat a wire of length one meter and radius ‘ 
’ by 
in time ‘ 
’. How many cells will be required to heat the wire of length two meter of the same radius by the same temperature in time ‘t’?
Text Solution
Verified by ExpertsA
Let 
be resistivity of the material of the wire and 
be radius ofthe wire.
Therefore, resistance of 1 
wire is
Let 
be emf of each cell. In first case, 10 cells each of emf 
are connected in series to heat the wire of length 1 
by
in time 
(i)
In second case,
Resistance of same wire of length 
is
Let 
cells each of emf 
are connected in series to heat the same wire of length 2 
, by the same temperature 
in the same time 
(ii) Divide (ii) by (i), we get
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