Question

An immersion heater has a power rating of 1500 watts. it is used to heat water for coffee. how long (in minutes) should it take to bring 0. 7 l of water from room temperature (20°c) to 80°c?

Answer 1

1.96 minutes long should it take to bring 0. 7 l of water from room temperature (20°c) to 80°c.

To find the answer, we have to know about the heat energy.

How to find the time taken to raise the temperature?

• It is given that,

                    $Power,P=1500W\\Volumw, V=0.7L\\T_1=20^0C \\T_2=80^0C$

• We have to find mass of water first, and the expression is,

                   $m=\rho V=1kg/L*0.7L=0.7kg$

• Heat energy required to raise the temperature from 20 to 80 degree Celsius is,

                    $Q=mc\Delta T=0.7*4182(80-20)\\Q=1.76*10^5J$

where, c equals to 4182J/kg°C.

• This energy can be related with power and then the time will be,

                     $t=\frac{E}{P} =\frac{1.76*10^5}{1500} =117.3s=1.96minutes.$

Thus, we can conclude that, 1.96 minutes long should it take to bring 0. 7 l of water from room temperature (20°c) to 80°c.

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