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  • It takes 16 min to boil some water in an electric kettle. Due to some defect it becomes necessary to remove 10% turns of the heating coil of the kettle. After repairs, how much time will it take to

It takes 16 min to boil some water in an electric kettle. Due to some defect it becomes necessary to remove 10% turns of the heating coil of the kettle. After repairs, how much time will it take to boil the same mass of water?

Option: 1

 17.7 min


Option: 2

 14.4 min  


Option: 3

20.9 min  


Option: 4

13.7 min


Answers (1)

best_answer

If N be the initial number of turns in the coil ad r be the radius of coil, then its resistance,
\begin{aligned} &\mathrm{ R=\rho \frac{L}{A}=\rho \frac{N 2 \pi r}{A} \text { or } \frac{V^2 t A}{4.2 \rho N 2 \pi r}=Q=m s d \theta }\\ &\mathrm{ \text { Or } \frac{t}{n}=\frac{m s d \theta \times 4.2 \rho \pi r}{V^2 A}=\mathrm{constant} }\\ &\mathrm{ \text { Or } \frac{t_1 / N_1}{t_2 / N_2}=1 \text { or } t_2=\frac{N_2}{N_1} \quad t_1=\left(\frac{\frac{9}{10} N_1}{N_1}\right) t_1=\frac{9}{10} \times 16 \mathrm{~min}}\\ \end{aligned}

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Ritika Harsh

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