An electric kettle contains 0.50 kg of water at 20 ∘C20\ ^\circ\text{C}20 ∘C.
The kettle is switched on and heats the water to 100 ∘C100\ ^\circ\text{C}100 ∘C.
Describe how energy is transferred from the mains supply to the water when the kettle is switched on.
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 needed to heat the water from 20 ∘C20\ ^\circ\text{C}20 ∘C to 100 ∘C100\ ^\circ\text{C}100 ∘C.
The energy transferred from the mains is greater than your answer to (b).
Suggest one reason why.
44 exam-style questions on OCR GCSE Physics 7.1 Work done, covering 7.1.1 Conservation of energy in a closed system, 7.1.2 Energy stores and transfers, 7.1.3 Energy changes by heating, forces and current, 7.1.4 Quantifying energy transfers in a system, and 7.1.5 Kinetic, elastic and gravitational potential energy. Each one has a worked solution and a mark scheme showing where the marks go.