A) 90 watts
B) 80 watts
C) 70 watts
D) 75 watts
Correct Answer: A
Solution :
Let \[R\] be the resistance of each resistor. In series, net resistance, \[{{R}_{1}}=3R\] \[\therefore \]Power dissipated, \[{{P}_{1}}=\frac{{{V}^{2}}}{{{R}_{2}}}=\frac{3{{V}^{2}}}{R}\] When the resistors are connected in parallel, then net resistance,\[{{R}_{2}}=\frac{R}{3}\] \[\therefore \]Power dissipated,\[{{P}_{2}}=\frac{{{V}^{2}}}{{{R}_{2}}}=\frac{3{{V}^{2}}}{R}\] \[\therefore \] \[\frac{{{P}_{2}}}{{{P}_{1}}}=\frac{(3{{V}^{2}}/R)}{({{V}^{2}}/3R)}=9\] \[\Rightarrow \] \[{{P}_{2}}=9\times {{P}_{1}}=9\times 10=\mathbf{90}\]watts
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