A continuous flow water heater (geyser) has an electrical power rating = 2 ,,kW and efficienty of co

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10-1.Thermometry, Thermal Expansion and Calorimetry

hard

A continuous flow water heater (geyser) has an electrical power rating $= 2 \,\,kW$ and efficienty of conversion of electrical power into heat $ = 80 \%$. If water is flowing through the device at the rate of $100 \,\,cc/sec$, and the inlet temperature is $10^o C$, the outlet temperature will be ....... $^oC$

A

$12.2$

B

$13.8$

C

$20$

D

$16.5$

Solution

$1 \mathrm{cc}$ of water has a mass of $1 \mathrm{g}$

Flow rate is $m=100 g / s$

$Q=2000 \times 0.8=1600 W$ or $\mathrm{J} / \mathrm{s},$ since the efficiency is $80 \%$

$Q=m c \Delta T,$ where $m$ is mass flow rate in $\mathrm{kg} / \mathrm{s}$

$1600=100 \times 4.2 \times(T-10) \Rightarrow T=13.8^{\circ} \mathrm{C}$

Standard 11

Physics

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