EasyPhysicsHigh School (11–12)Heat & Thermodynamics › Calorimetry and Change of StateNumerical

A 1200 W stove passes 75% of its heat to a pan of 2.0 kg of water at 25 °C.

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

A $1200\ \text{W}$ stove passes $75\%$ of its heat to a pan of $2.0\ \text{kg}$ of water at $25\ ^\circ\text{C}$ . How long until the water boils? How much longer to boil away $0.50\ \text{kg}$ of it? (Water $4186\ \text{J kg}^{-1}\text{K}^{-1}$ ; latent heat $2.26 \times 10^{6}\ \text{J/kg}$ .)

Need a reminder? The key ideaShow

During a change of state the temperature stays steady and $Q = mL$ : ice melting $3.34 \times 10^{5}\ \text{J/kg}$ , water boiling $2.26 \times 10^{6}\ \text{J/kg}$ . The same heat comes out on freezing or condensing.

The worked solution

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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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