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An electric kettle has two coils of different power. When one coil is switched on, it takes 30 minutes to boil a certain amount of water and when second coil is switched on, it takes 45 minutes to boil same amount of water. Then |
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Answer» It takes 150 minutes to boil same amount of water when both the coils are used in series combination. `H_(1)=H_(2)implies30/(R_(1))=45/(R_(2))implies3R_(1)=2R_(2)` `H_("series')=(V^(2))/((R_(1)+R_(2))) t_(s)=(V^(2))/((R_(1)+3/2R_(1))) t_(s)=H_(1)=(V^(2))/(R_(1))(30xx60)` `implies t_(s)=(30xx60)5/2 =75` min `H_(P)=((V^(2))/(R_(1))+(V^(2))/(R^(2)))t_(P)+((V^(2))/(R_(1))+(2V^(2))/(3R_(1)))t_(P)` `implies(5V^(2))/(3R_(1)) t_(P)=(V^(2))/(R_(1))(30xx60)` `t_(P)=(3xx30xx60)/5=18` min |
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