An electric kettle contains 500 g of water at 20 ∘C20\ ^{\circ}\text{C}20 ∘C.
The kettle heats the water to 100 ∘C100\ ^{\circ}\text{C}100 ∘C.
The specific heat capacity of water is 4200 J/kg ∘C4200\ \text{J/kg}\ ^{\circ}\text{C}4200 J/kg ∘C.
Use the equation: change in thermal energy=mass×specific heat capacity×change in temperature\text{change in thermal energy} = \text{mass} \times \text{specific heat capacity} \times \text{change in temperature}change in thermal energy=mass×specific heat capacity×change in temperature
Calculate the energy transferred to the water.
Give your answer in kJ\text{kJ}kJ.
The kettle transfers more energy than your answer to (a).
Explain why.
The kettle is left switched on and 20 g of the water boils away.
The specific latent heat of vaporisation of water is 2 260 000 J/kg2\,260\,000\ \text{J/kg}2260000 J/kg.
Use the equation: thermal energy for a change in state=mass×specific latent heat\text{thermal energy for a change in state} = \text{mass} \times \text{specific latent heat}thermal energy for a change in state=mass×specific latent heat
Calculate the energy needed to boil away the water.
44 exam-style questions on OCR GCSE Physics 1.2 Changes of state, covering 1.2.1 Conservation of mass during changes of state, 1.2.2 Physical and chemical changes, 1.2.3 Heating, temperature and changes of state, 1.2.4 Specific heat capacity and specific latent heat, 1.2.5 Internal energy and temperature change, and 1.2.6 Energy transfer during a change of state. Each one has a worked solution and a mark scheme showing where the marks go.