A) 5
B) 20
C) 10
D) 2.5
E) 1.25
Correct Answer: B
Solution :
Heat produced by the heater \[H=\frac{{{V}^{2}}}{R}\times t\] For 220 V heater heat produced \[{{H}_{1}}=\frac{{{(220)}^{2}}}{R}\times 5\] For 110 V heater \[{{H}_{2}}=\frac{{{(110)}^{2}}}{R}\times t\] Now, \[{{H}_{1}}={{H}_{2}}\] \[\frac{110\times 110}{R}\times t=\frac{220\times 225\times 5}{R}\] \[t=20\text{ }min\]
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