Unit 9.4 Sound and energy
Outline of unit:
In this unit, learners draw and label waveforms, explore transverse and longitudinal waves and how they transfer energy. Learners will consider that sound travels as longitudinal waves and that electromagnetic waves travel as transverse waves. They will also learn about principles of wave interference using sound waves.
Learners go onto explore the theory of conservation of energy and begin to apply it to energy transfers and heat dissipation. As part of this learners will discuss and explain the difference between heat and temperature before considering transfer of energy by conduction convection and radiation and cooling by evaporation.
This unit provides opportunities for learners to carry out practical work and to consider models, including their strengths and limitations.
Recommended prior knowledge or previous learning required for the unit:
Learners will benefit from previous experience of:
● describing how sound waves are transmitted by the vibration of particles
● knowing light travels as waves
● understanding sound and light waves can be reflected by some surfaces
● knowing energy changes occur as a result of an event or process
● knowing some energy is dissipated and becomes less useful during energy changes
● describing how energy may be transferred mechanically with forces, electrically with an electric current and thermally by heating.
Suggested examples for teaching Science in Context:
9SIC.02 Describe how science is applied across societies and industries, and in research.
Sound has many applications in industry and society including in medical technology. Learners can consider what technologies use sound, and how the sound waves are manipulated for example in ultrasound equipment.
9SIC.03 Evaluate issues which involve and/or require scientific understanding.
Learners discuss energy efficiency and the role of house insulation. They can use their understanding of heat dissipation to discuss the pros and cons of house insulation and when it is appropriate to support or hinder heat dissipation.
9SIC.05 Discuss how the uses of science can have a global environmental impact.
Scientific understanding about sound has allowed humans to develop new technologies, including the development of sonar and other underwater technologies.
However some of these technologies have an impact on the marine environment and organisms. Learners can research and discuss the impact of underwater sounds from human activities.
Learning objective Key vocabulary Possible models and representations Possible misconceptions 9Ps.01 Draw and
interpret waveforms, and recognise the link between loudness and amplitude, pitch and frequency.
oscillation, transverse, longitudinal, compression, rarefaction, amplitude, frequency, wavelength, peak, trough, pitch, frequency, loudness, waveform
A ‘slinky’ toy (a compressed helical spring) can be used to model how a longitudinal wave (e.g. a sound wave) travels. In this model, each coil represents an air molecule. Each wave of compression represents a sound wave. Sound travels through the air (the wave moves), but the air (the coil) does not travel with the sound; like the coils, the air particles oscillate.
Some learners may think that waves transfer physical matter rather than energy. Using a length of rubber tubing, where the tube will allow a wave to propagate, will demonstrate that a transverse wave transfers energy without transferring matter.
Some learners may think that sound can travel through an empty space (a vacuum). This is a common misconception as many science fiction films show sound being transmitted through vacuum. It may be addressed by demonstrating, or showing a video, of sound in a bell jar under vacuum.
9Ps.02 Use waveforms to show how sound waves interact to reinforce or cancel each other.
constructive interference, destructive interference, in phase, out of phase, superpose, superposition, reinforce, cancel,
waveform
Superposition of waves can be modelled by dropping marbles into water at different locations and observing the wave patterns produced when two waves interact.
Learners may believe that waves have to be identical to interact. This can be disproved by showing a variety of diagrams of different
waveforms interacting, including some interactions where the waveforms partially cancel or reinforce each other.
9Pf.03 Know that energy is conserved, meaning it cannot be created or destroyed.
law of conservation of energy, chemical store, energy store, kinetic energy, thermal energy, gravitational potential, elastic potential energy, energy dissipation
Conservation of energy can be modelled using toy blocks (representing units of energy): the blocks can be transferred between different stores but they are not created or destroyed.
Learners could also be introduced to Sankey diagrams (without numbers) and use them to represent conservation of energy.
Learners often think that energy may be created and/or destroyed. This misconception is reinforced by the common misuse of language (e.g. The Sun
‘makes energy’ by nuclear fusion rather than
‘releases energy’). This misconception should be addressed throughout this unit by consistently modelling the correct use of language.
9Pf.02 Describe the difference between heat and temperature.
thermal store, heat, energy transfer, temperature, joules (J), degrees Celsius (°C), kinetic theory, kinetic energy, solid liquid, gas
Kinetic theory can be used to model temperature, as temperature is a measure of the kinetic energy particles in a material or object have. Learners hold a cloth sheet (or blanket) on all sides with about ten lightweight balls placed in the centre. The balls initially represent the particles of a solid when the sheet is just gently moved: they are touching, form a regular pattern but are vibrating slightly. Jiggling the sheet a little more results in the balls breaking away from the pattern and their separation increases. Some balls may briefly fly into the air:
this now represents the particles in a liquid.
Learners may think that heat and temperature are the same thing. This misconception is reinforced by the common misuse of language e.g. The food should be cooked using a ‘high heat’ rather than
‘high temperature’. This misconception will be addressed through this unit.
Some learners may think that particles in a cold substance are not moving. The kinetic theory model should be used to address this misconception.
As water is commonly used to model an increase in
Shaking the sheet vigorously results in the balls being separated widely and being ejected from the sheet completely: this represents the particles of a gas.
The difference between heat and temperature can be shown by adding more balls to the sheet without changing the movement of the sheet. For example, quadrupling the number of balls (representing quadrupling the number of particles / mass) for the same amount movement would represent four times the amount of heat.
kinetic energy of particles/atoms during a change of state, some learners may not realise other
substances behave in a similar way. To address this, show other substances changing state and challenge learners to draw the particle diagrams for the changes. Gallium would melt on a learner’s gloved hand. Volatile liquids (e.g. petroleum ether, rubbing alcohol) that evaporate rapidly could also be used, taking care as they are flammable.
9Pf.04 Know that thermal energy will always transfer from hotter regions or objects to colder ones, and this is known as heat
dissipation.
temperature, heat
thermal, dissipation, Heat dissipation can be modelled using water and food colouring. Mix blue food colouring with cold water to represent a cold region of a substance.
Add a few drops of red food colouring to hot water to represent a hot region. Gently pour the red, warm water on top of the blue, cold water. Over time, the red coloured water will spread throughout the entire body of water, changing the colour of the colder water.
Emphasise that the process of the red food colouring spreading is an example of diffusion which is caused by the water and food colouring particles’ movement. The process of heat dissipation is similar but can happen between remote materials and objects (e.g. between separate objects in an insulated container).
Heat dissipation can also be shown
diagrammatically using colours to show different temperatures with arrows indicating the dissipation of heat.
Learners may think that energy is a substance that can ‘flow’ from place to place. Some models and experiments may reinforce this misconception. It may be addressed by evaluating the strengths and limitations of models and experiments when they are used.
9Pf.05 Describe thermal transfer by the processes of conduction, convection and radiation.
conduction, convection, convection current, radiation, conductor, insulator, thermal transfer
The three different methods of heat transfer can be modelled using three bean bags given to learners.
The bean bags can be returned to you by passing (conduction), carrying (convection), or throwing (radiation).
It is common for learners to state that ‘heat rises’
instead of stating that ‘hot fluids and gases rise’
when describing convection. It may be addressed by insisting on learners using correct terminology when describing heat transfer processes. The process of convection is also linked to density of a
Conduction can be represented using a particle diagram of a solid being heated at one end. The particles at the end being heated vibrate more as energy is transferred to them. These particles collide with their neighbouring particles, transferring the energy to them and so transferring the energy throughout the material. Energy will transfer from one end to another until the thermal energy stores at each end are the same (both ends are at the same temperature).
Convection can be represented by a diagram showing a convection current of a fluid (liquid or gas) being heated from the bottom. Particles close to the thermal energy store get hot and start to vibrate more and move faster. They move further apart and become less dense. The hot fluid rises, and colder denser fluid takes up its place and is heated in turn. As the heated fluid rises it cools, becomes denser and sinks. This process continues until the fluid is the same temperature throughout.
Radiation can be represented by thermal images.
substance which has been previously covered.
Many learners believe that only ‘hot’ objects emit infrared radiation rather than all objects with a temperature higher than absolute zero. It may be addressed by showing thermal images of cooler objects and explaining the colour still represents heat. Black would represent absolute zero and a lack of heat being radiated by an object.
Learners may think that convection currents are caused by ‘potassium manganate VII’ because it has a ‘scientific sounding name’. Referring to it as a
‘dye’ can avoid this misconception.
9Pf.06 Explain cooling by
evaporation. change of state,
evaporation Cooling by evaporation can be represented using the familiar example of sweating. Sweating can be modelled by dabbing a little cold water on the back of the hand using tissue paper / cotton wool and then blowing gently.
Some learners may think that when water evaporates it turns to steam, when it in fact
becomes water vapour. This misconception should have been challenged at an earlier stage. However, if it remains, clarify that pure water does not boil until its temperature reaches100°C. Water
evaporates at all temperatures between its freezing point and its boiling point; the rate of evaporation increases with temperature.