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  • A wire of length and 3 identical cells of negligible internal resistances are connected in series. Due to the current, the te

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 \Delta 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 \Delta T in the same time. The value of N is :

Option: 1

4


Option: 2

6


Option: 3

8


Option: 4

9


Answers (1)

best_answer

In the first case \frac{(3 E)^2}{R} \cdot t=m s \Delta T                           ...(1)

                           \left[H=\frac{V^2}{R} \cdot t\right]

When length of the wire is doubled, resistance and mass both are boubled. Therefore, in the second case,

\frac{(N E)^2}{2 R} \cdot t=(2 m) s \Delta T                                                 ...(2)

    Dividing Eq. (2) by (1), we get 

\frac{N^2}{18}=2 \text { or } N^2=36 \text { or } N=6

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avinash.dongre

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