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An electric kettle has two windings. When one of them is switched on, the water in the kettle begins to boil in 15 minutes, and when the other is switched on it takes 30 minutes for water to boil. If the two windings are joined in series and switched on, water in the kettle begin to boil after time: (in minutes) [Assume that the kettle loses no heat to the surroundings] |
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Answer» 45 `therefore` When winding 1 is PRESENT `p=v^2/R_1 therefore m_(v ATER)L_f=V^2/R_1 times 15` For `2^(nd)` winding `P=V^2/R_2 therefore m_(VATER)L_f=V^2/R_1 times 15`………(ii) When the winding are joined in series, `R_(eq)=(R_1+R_2) therefore P=V^2/((R_1+R_2)) therefore m_(vater) L_f=(V^2/(R_1+R_2))t`.......(iii) from eqs (i), (ii) and (iii), t=45 min |
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