Current Electricity Charging Discharging Of Capacitors Question 735
Question: It takes 12 minutes to boil 1 liter of water in an electric kettle. Due to some defect it becomes necessary to remove 20% turns of heating coil of the kettle. After repair, how much time will it take to boil 1 liter of water?
Options:
A) 9.6 minute
B) 14.4 minute
C) 16.8 minute
D) 18.2 minute
Show Answer
Answer:
Correct Answer: A
Solution:
[a] As voltage of appliance remains constant, the amount of heat produced is given by, $ H=\frac{V^{2}}{R}t $ …(i) When resistance is reduced by 20%, new resistance is $ R’=R-0.2R=0.8RR’=R-0.2R=0.8R $
$ H’=\frac{V^{2}}{0.8R}t’ $ ?(ii) Equating Eqs. (i) and (ii), we get $ \frac{V^{2}}{R}t=\frac{V^{2}}{0.8R}t’ $
$ \Rightarrow t’=0.58t=0.8\times 12=9.6\text{ min} $
BETA
