An electric kettle used to prepare tea, takes 2 minutes to boil 4 cups of water (1 cup contains 200 cc of water) if the room temperature is `25^@ C`, (a) If the cost of power consumption is `Re 1.00` per unit `(1 unit = 1000 watt-hour)`, calculate the cost of boiling 4 cups of water. (b) What will be the corresponding cost if the room temperature drops to `5^@ C`?

Answer

(i)`21 palse`(ii)27 palse`

Explanation

Volume of water in `4` cups
`upsilon = 4 xx 200 = 800 c.c`
mass of wire m = volume `xx` desity
`= 800 xx 1 = 800` gram
(a) Energy spent is boding the water `= ms d theta `
`= 800 xx 1 xx (100 - 25)` cal
`= 800 xx 75 xx 4.2J`
`= (800 xx 75 xx 4.2)/(3.6) xx 10^(6)) kWh =0.07 kWb`
cost of bospend in boliing the water `= 0.07 xx 3 = 0.21 Rs = 21` pulse
(ii) Energy spent in boding the water
`= 800 xx 1 xx (100 - 5) cal`
`= 800 xx 95 xx 4.2J`
`= (800 xx 95 xx 4.2)/(3.6) xx 10^(6)) kWh =0.09 kWb`
cost of boiling the water `= 0.09 xx 3 = 0.27 Rs = 21` pulse