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A wire of length *L* and 3 identical cells of negligible internal resistances are connected in series. Due to current, the temperature of the wire is raised by Δ*T* in a time *t*. A number *N* of similar cells is now connected in series with a wire of the same material and cross–section but of length 2 *L*. The temperature of the wire is raised by the same amount Δ*T* in the same time *t*. the value of *N* is

(1) 4

(2) 6

(3) 8

(4) 9