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VITEEE 2010 Paper

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Question : 3 of 120

Marks: +1, -0

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

12.6 min
4.2 min
6.3 min
8.4 min

Solution:

Heat taken by water when its temperature changes from 20°C to 100°C.

H_{1}=mc(\theta_{2}-\theta_{1})

=1000\times 1\times (100-20)\,\text{cal}

=1000\times 80\times 4.2\;\text{J}

Heat produced in time

t

due to current in resistor

H_{2}=V\times i\times t= 220\times 4\times t\;\text{J}

According to question,

220\times 4\times t=1000\times 80\times 4.2

⇒

t=\frac{1000\times 80\times 4.2}{220\times 4}

=381.8\;\text{s}=6.3\;\text{min}

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