Teacher Tip: Based on the Physics Narrative and the Teaching and Learning Issues

Ideas to emphasise here

• construct the source-medium-detector model
• show illumination as a process where something travels
• build a helpful model of how illumination diminishes
• emphasise that there is a finite trip time from source to detector
• draw out the role of light in enabling seeing
• bring to mind the role of reflection in seeing luminous objects
• always explicitly accounting for reductions in brightness
• the physical aspect of the transmission of light
• light is emitted by luminous objects
• light travels in straight lines
• objects are transparent, translucent or opaque
• objects that are opaque cast shadows
• we only see non-luminous objects when light bounces off them
• sometimes, if the object is shiny, this bouncing can form an image (mirrors)
• light is detected by our eyes
• light travelling is the spreading of the vibrations
• link reductions in intensity with distance from the source
• link delays in hearing sounds compared to seeing sights to the trip time of propagation from the source
• that light travels through a vacuum (from the Sun and other stars)

Teacher Tip: Work through the Physics Narrative to find these lines of thinking worked out and then look in the Teaching Approaches for some examples of activities.

Strategies for supporting learning

• identify source and detector
• separate luminous from non-luminous
• draw out children's ideas about seeing
• connect seeing to the source-medium-detector model
• build an explicit model of seeing
• organise what children have observed into a coherent whole
• build three-dimension models where illumination is important
• draw out what children believe about the Earth-Moon-Sun system and how this is related to everyday phenomena
• avoid restricting the idea of reflection to shiny surfaces
• reinforce the role of reflection in seeing
• connect seeing to both specular and diffuse reflections
• show clear examples of the phenomena
• introduce a wide range of surfaces from which reflection happens
• put the source–medium-detector model to use; note the lack of tangible medium
• connect light sources (luminous objects) to how we detect them
• connect seeing to the source-medium-detector model
• separate the luminous object that generates the vibration from the propagation of the vibration, which is also a movement
• emphasising that all lights have a source
• emphasising that we only see non-luminous objects when light bounces off them
• tracing the chain from source to detector, via object, often
• connect human vision to what other species can see (for example snakes can see in IR and insects in UV)
• link each light seen back to the source, via the object it bounces off
• Look at different early models of seeing to see which ones fit the evidence of our experiments.

Teacher Tip: These are all related to findings about children's ideas from research. The teaching activities will provide some suggestions. So will colleagues, near and far.

Avoid these

• speaking or acting as if light was just there
• assuming that how we see is well understood
• assuming that seeing is all accounted for by the physics
• conflating rays (the theoretical construct) with light beams (the physical)
• running together what is noticed and recorded with what is modelled
• restricting examples of reflection to only, or mostly, shiny surfaces
• replacing experiences of real and interesting phenomena with a series of ad-hoc memorised rules
• not showing how an understanding of simple situations is linked to a wide variety of phenomena in the lived-in world
• introducing the technical term ray
• using specious energy descriptions
• drawing or showing transverse waveforms
• asserting that light is a wave without clarifying explanation of the idea of a wave – this is hard
• introducing wavelength, frequency, or energy of light

Teacher Tip: These difficulties are distilled from: the research findings; the practice of well-connected teachers with expertise; issues intrinsic to representing the physics well.