Energy Resources and Energy Transfers
6 marks · NormalThe diagram shows a rectangular solar heating panel used to heat water for a home. Water enters the pipe at A and leaves at B after flowing through the panel. The inside of the panel is painted matt black and covered by a glass sheet.
Explain why the inside surface of the panel is painted matt black.
Suggest one reason for covering the panel with a glass sheet.
State and explain which energy transfer process is mainly responsible for transferring energy from the Sun to the panel.
Describe how convection helps heat water inside the pipe.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Matt black absorbs infrared radiation from the Sun more efficiently than shiny or white surfaces, maximizing absorption of thermal energy for heating the water.
(b) To prevent heat loss / let sunlight in but trap heat (acts as insulator / greenhouse effect)
(c) Radiation is the main process. Thermal (infrared) radiation from the Sun passes through space and the atmosphere to the panel, transferring energy without the need for a medium.
(d) Warm water rises, cold water sinks, setting up a convection current that spreads the heat through the water.
Show mark scheme and worked solution
Marking points
B1 (a) · 2 marks · States 'matt black is best absorber of radiation' (1), links to maximising energy/heat for water (1).
B2 (b) · 1 mark · Give a correct reason for using glass: traps heat/acts as insulator/allows sunlight in.
B3 (c) · 2 marks · States 'radiation' (1) and gives correct reasoning relating to transfer from Sun through space/atmosphere (1).
B4 (d) · 1 mark · States convection current: warm water rises, cold sinks (or equivalent correct description).
Worked solution
a) Matt black surfaces absorb more heat by radiation than shiny or white surfaces, ensuring more energy is transferred to the water.
b) The glass sheet reduces heat loss from the panel while letting sunlight enter.
c) The main energy transfer from the Sun to the panel is by radiation (infrared). Radiation can travel through space and air without needing a material.
d) Convection: heated water rises in the pipe, cooler water sinks, setting up a current that distributes heat.