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An electric kettle takes 4 A current at 220 V. How much time will it take to boil 1 kg of water from temperature 20°C? The temperature of boiling water is 100°C.

Asked in CBSE AIPMT 2008 · Heating and power in resistors

• (1) 12.6 min
• (2) 4.2 min
• (3) 6.3 min
• (4) 8.4 min

Step-by-step solution

Why the other options are wrong

• (1) Twice the correct time; it would need half the power (440 W). No single slip with these numbers gives it.
• (2) No single slip gives 4.2 min; it would need about 1330 W, half as much again as 880 W.
• (4) No single slip gives 8.4 min; it is about 1.3 times the correct time.

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