A wire of length L and 3 identical cells of negligible internal resistances are connected in series. Due to the current, the temperature of the wire is raised by ΔT 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 the length 2 L. The temperature of the wire is raised by the same amount `Delta T` in the same time t. the value of N is
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