# NEET Questions Solved

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 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 of length 2 L. The temperature of the wire is raised by the same amount ΔT in the same time t. the value of N is

(1) 4

(2) 6

(3) 8

(4) 9

(2) Let R and m be the resistance and mass of the first wire, then the second wire has resistance 2R and mass 2m. Let E = emf of each cell, S = specific heat capacity of the material of the wire. For the first wire, current ${i}_{1}=\frac{3E}{R}$ and ${i}_{1}^{2}Rt=mS\Delta T$

For the second wire, ${i}_{2}=\frac{N\text{​}E}{2R}$ and ${i}_{2}^{2}\left(2R\right)t=2mS\Delta T$. Thus, ${i}_{1}={i}_{2}$ or $N=6$.

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