Edexcel iGCSE Physics (4PH1) 5.1 Units Exam Style Question Paper 2B - New Syllabus
Question
The photograph shows a water bath that a technician uses to heat some water.
(a) The water bath is filled with water at an initial temperature of \(15^\circ\mathrm{C}\). Calculate the initial temperature of the water in kelvin.
(b) The technician heats the water to a final temperature of \(60^\circ\mathrm{C}\).
(i) Describe how the energy of the water molecules changes as the temperature of the water increases.
(ii) The table shows some information about the heating element in the water bath and the heating process.
Calculate the energy transferred by the heating element in the water bath during the heating process.
(iii) Calculate the mass of water being heated. Assume that all the energy is transferred to the thermal store of the water.
[for water, specific heat capacity = \(4200\,\mathrm{J\,kg^{-1}\,^\circ C^{-1}}\)]
(c) Some water evaporates as a gas from the water bath.
(i) Describe the arrangement of particles in a gas.
(ii) Describe two differences between evaporation and boiling.
Syllabus Topic Codes (Edexcel International GCSE Physics 4PH1):
• 5.18–5.19: Temperature, Molecular Speed, and Kinetic Energy — part (b)(i)
• 2.4–2.5: Power, Current, Voltage, and Electrical Energy Transfer — part (b)(ii)
• 5.12–5.13P: Specific Heat Capacity and Thermal Energy Change Equation — part (b)(iii)
• 5.10P: Particle Model of Solids, Liquids, and Gases — part (c)(i)
• 5.9P: Changes of State — part (c)(ii)
▶️ Answer/Explanation
(a) Temperature in kelvin [1 mark]
Use the conversion:
\(T_{\mathrm{K}}=T_{^\circ\mathrm{C}}+273\)
\(T_{\mathrm{K}}=15+273=288\,\mathrm{K}\)
\(\boxed{288\,\mathrm{K}}\)
(b)(i) Energy of the water molecules [2 marks]
As the temperature increases, the energy of the water molecules increases.
The average kinetic energy of the molecules increases, meaning that the molecules move faster on average.
(b)(ii) Energy transferred by the heating element [3 marks]
Use:
\(E=VIt\)
The heating time is \(45\,\mathrm{min}\), so convert it to seconds:
\(t=45\times60=2700\,\mathrm{s}\)
Substitute \(V=230\,\mathrm{V}\), \(I=1.5\,\mathrm{A}\), and \(t=2700\,\mathrm{s}\):
\(E=230\times1.5\times2700\)
\(E=931\,500\,\mathrm{J}\)
Therefore:
\(\boxed{E\approx9.3\times10^5\,\mathrm{J}}\)
(b)(iii) Mass of water [3 marks]
Use the thermal energy equation:
\(Q=mc\Delta T\)
The temperature change is:
\(\Delta T=60-15=45^\circ\mathrm{C}\)
Since all the energy is transferred to the thermal store of the water:
\(9.3\times10^5=m\times4200\times45\)
Rearranging:
\(m=\dfrac{9.3\times10^5}{4200\times45}\)
\(m\approx4.92\,\mathrm{kg}\)
\(\boxed{m\approx4.9\,\mathrm{kg}}\)
(c)(i) Arrangement of particles in a gas [2 marks]
- The particles are arranged randomly.
- The particles are widely spaced with large gaps between them.
(c)(ii) Evaporation and boiling [2 marks]
- Boiling occurs at a specific or fixed temperature, whereas evaporation can occur at any temperature.
- Boiling occurs throughout the liquid, whereas evaporation occurs only at the surface.