Reflection
Light, Sound and Waves

Seeing things - Teaching Approaches

Classroom Activity for 5-11

A Teaching Approach is both a source of advice and an activity that respects both the physics narrative and the teaching and learning issues for a topic.

The following set of resources is not an exhaustive selection, rather it seeks to exemplify. In general there are already many activities available online; you'll want to select from these wisely, and to assemble and evolve your own repertoire that is matched to the needs of your class and the equipment/resources to hand. We hope that the collection here will enable you to think about your own selection process, considering both the physics narrative and the topic-specific teaching and learning issues.

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Selecting and developing activities for seeing things

Visible Light
Light Sound and Waves

Selecting and developing activities for seeing things

Classroom Activity for 5-11

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 Narratives to find these lines of thinking worked out and then look in the Classroom Activities 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.

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A sequence to develop ideas about seeing

Visible Light
Light Sound and Waves

A sequence to develop ideas about seeing

Classroom Activity for 5-11

Meeting reality: valuable experiences

Seeing is a very significant sense to humans, and some images evoke strong emotional responses. The physicality of the light is really important, both of making connections to the underpinning waves and for establishing a context for the learning and the emotional hooks.

  • Noticing lights from many different sources
  • Using a large dark space to explore 'not-seeing in the dark'
  • Exploring collections of sources that make lights of different brightness
  • Tracing out the paths of light from source to detector, via other objects

Teacher Tip: As many of these as possible should be direct physical experiences, rather than mediated through video clips. This locates the learning in the lived-in world of the child, and grounds the learning in specific physical circumstances.

A sequence for developing the idea

This is a suggested sequence of activities, so a repertoire, on which to draw as you decide on a sequence to best suit the children in your own situation.

Teacher Tip: The ideas are developed in the Physics Narratives.

There are a large number of light sources in the everyday lived in world, and this activity begins bring them to children's notice. it can also be used to use the general idea of a light source.

Noticing lights


This activity compares natural and man-made lights, and begins to develop ways of describing the sources, and of thinking about how we come to see.

Lights in the environment


This is something of an extension activity, building on the noticing of light sources.

Survey: Lighting at home


This is in many ways the core activity where the focus strongly on the ways in which we see. The source-medium-detector model is at the core of this activity.

Seeing with light – an activity


An absence of light means we cannot see. Many children will not have experienced a total absence of light and may therefore not appreciate that some light is essential to seeing. This experience presents an opportunity to provide the experience and to work on the incorrect idea.

Totally in the dark!


Where there is no light, we cannot see. If light from a source does not travels to a particular location then we will not be able to see the source. Shadows are such locations. Here is the simple way of introducing shadows.

Introducing light sources and shadows


Light and darkness are extremes, but there are different brightnesses between total absence of light and very bright sunlight. Using a data logger may enable you to tell interesting story about the variation in brightness – but only if you choose an interesting place to make your measurement.

Tracking Brightness


Sharp shadows rely on light travelling in straight lines and therefore provides a very good contacts were beginning to talk about how you can decide where there are shadows and where there are not. Such an approach also begins the discussion about light travelling in straight lines, which is assumed by this activity.

In straight lines


This is a challenging activity out of which interesting discussions might grow.

Mirror writing


Messages from research and practice: specific tripwires for this idea

To illuminate an object requires a source from which the light travels. If you can see that illuminated object, then the light has bounced off the object and into your eye. So the journey is essential to seeing, and tracing out this journey is a common theme – and common difficulty – in teaching this topic. Many of the highlighted challenges are concerned with this journey from source to detector.

Light must travel from its source to the detector: or it will not be detected. Much of the language that we use about lighting obscures this essential travelling, and so children quite often do not think of light is travelling from source to detector.

Light is travelling between source and effect


Children have a number of different ideas on how we see, and it's a good idea to be aware of these in order to be able to challenge these ideas explicitly. In this way you will give children an opportunity to correct their ideas.

How do we see?


It is rather common for children to think the light gets used up on its way from the source. So it's worth challenging this particular idea head on.

How far can light travel?


For you to be able to see one thing light must travel from our thing to your eye. If the thing is not luminous ( so it does not glow, so providing its own lighting), then light must reflect from the thing for you to see it. So is not only mirrors that reflect – in fact these are a rather special form of reflection.

Reflection from any surface


Teacher Tip: These challenges and some suggestions for working with them are more fully explained in the Teaching and Learning Issues.

Representing and reasoning: doing physics

The journey the light takes in order to get from what you've seen to your eye is the idea at the centre of this topic. To see something is to receive light in your eye from that thing. No lighting: no sighting. Everything else is secondary. so building and using the source-detector representation is the major task of this topic.

To see something is to have light travel from our thing to your eye.

Seeing with light


The following pair of expositions are linked, in that the formation of shadows is a strong piece of evidence for light travelling in straight lines. Although this is not formally required for the children at this stage it is useful to have in your mind.

Light travelling in straight lines


Light meeting obstacles


Every thing that is not luminous requires light to reflect from it in order to be seen. Therefore anything that can be seen must reflect light

Not just mirrors


  • Light travels from a source to your eye, if you can see the source
  • If you obstruct the route, then you get a shadow
  • If not light goes into your eye from the source, then you cannot see it
  • Seeing many things relies on reflected light

Teacher Tip: Find out more from the Physics Narratives

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Noticing lights

Reflection
Light, Sound and Waves

Noticing lights

Classroom Activity for 5-11

What the Activity is for

To bring to children's attention the range and variety of lights that can be seen in different places in their local environment.

Also, to begin to think about and look for sources of lighting.

What to Prepare

  • identified and sampled locations, around the school
  • a recording frame

What Happens During this Activity

Choose three different sites around the school for the children to visit. Spend two or three minutes looking carefully to the different lights at that site. Discuss what you notice about the lights and make a record, either as a whole group or in small groups.

Here are some useful questions to help direct thinking:

Teacher: What lights can you see?

Teacher: Do you think the lamps you're seeing are close to you or far away?

Teacher: Can you give a reason why you think what you're seeing is close to you or far away from you?

Teacher: Can you see what is making the light?

Teacher: How do you think the light would change if you had seen it outdoors, say or in the classroom?

Teacher Tip: This activity can be repeated beyond the school grounds, perhaps also in the local area, or at home. A portable light meter would be invaluable.

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Lights in the environment

Reflection
Light, Sound and Waves

Lights in the environment

Classroom Activity for 5-11

What the Activity is for

Comparing natural and man-made lights.

This activity is useful to begin to develop a descriptive language for light (recognising the many qualities of the light in addition to the more common quantitative measures). We think it's good to recognise the richness of the sense of seeing, rather than focusing in too rapidly on brightness or colour as being the most easily quantified descriptions of the lights.

So this is an exploratory activity, and is therefore somewhat divergent.

What to Prepare

  • scouted locations where a range of natural and man-made lights can be seen

What Happens During this Activity

This approach can be used at any time in the children's exploration of light. It can be used as a starting point or to extend their understanding.

The children categorise the different lights that they see. You'll want to choose the categories with the abilities and interests of you class in mind. There are no rigid categories that are invariably useful at this early and exploratory stage. However you will want to start to differentiate between reflected sources of light and direct sources of light.

Safety note: Children should never look into the sun.

You'll want to explore a variety of different ways of noticing and noting the differences and similarities. Discussion here supports both reasoning and a variety of representations is likely to prove fruitful if encouraged. Here are some questions that we found useful to direct thinking:

Teacher: What would the world light like without humans on the planet?

Teacher: How can you explain to a friend that one light is from the Sun, whilst another is artificial?

Teacher: Can you block out light?

Teacher Tip: This can be used specifically in a science session or could lead to a cross-curricular imaginative writing activity in which the ideas of light as travelling vibrations can be explored.

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Survey: lighting at home

Reflection
Light, Sound and Waves

Survey: lighting at home

Classroom Activity for 5-11 11-14

What the Activity is for

This activity helps to make the link between studies of light at school and lighting in the home. It will provides lots of points of discussion relating to the pros and cons of different kinds of bulbs.

What to Prepare

  • devise a tabulated starter support sheet that will get your class off on the right lines, if necessary

You might include, as headings:

  • room
  • light function
  • light fitting
  • bulb
  • colour
  • power
  • direct/indirect lighting

What Happens During this Activity

This homework activity involves the pupils in making a survey of the lighting in their home. You will need to provide the class with a table in which they can record their findings.

Clarify with the class what each of the headings means – their descriptions should be simple enough for the rest of the class to understand.

Room: what is the room used for?

Light fitting: the kind of fitting, e.g. chandelier, reading lamp, strip light

Type of bulb: filament, fluorescent, energy-saver, halogen

Colour: most will be white

Power (in watts): If electrical power has been covered in lessons on electricity this exercise will provide a useful link. Otherwise introduce the idea that the power of the bulb is a measure of the amount of energy (heat and light) shifted every second. The higher the power, the brighter the bulb.

Direct or indirect lighting: Do the lamps provide direct illumination to the room or is the light reflected off the wall or ceiling first?

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Seeing with light

Reflection
Light, Sound and Waves

Seeing with light - an activity

Classroom Activity for 5-11 11-14

What the Activity is for

Seeing beams of light.

This is part of a suggested sequence:

A repertoire to develop the idea of seeing


Pupils will very often agree that to be able to see, light must enter the eye. However, it is possible to set up situations where this apparently firmly-fixed belief can be productively challenged, and thereby strengthened. This is the aim for this demonstration.

What to Prepare

  • a source of fine dust – board duster or talc
  • a low power laser that provides an intense, fine beam of light

Safety note: Take care to ensure that light from the laser cannot pass directly into anyone's eyes. A class 2 laser should be used, although a laser pointer can be used if under the careful control of the teacher. You should be aware, however, that some laser pointers are incorrectly assigned a relatively low power rating and are potentially more dangerous than they might appear.

Even if a laser beam does enter the eye, the blink-aversion response is sufficiently fast to avoid any damage to the retina except with the most powerful lasers.

What Happens During this Activity

Set up the laser so that, when switched on, the beam travels across the front of the room, landing on a white screen so that the red spot is clearly visible.

Start by describing the set-up to the pupils, showing the laser and pointing to the screen across the room at which the beam is directed. For the sake of this demonstration, all that the pupils need to know is that the laser provides an intense, or very powerful, beam of light.

Explain that you are going to put the room lights out in a moment and ask the pupils to predict what they will see when the lights are out (with a good black-out) and the laser is switched on. This is where the pupils' ideas about seeing are challenged.

Challenging predictions

Former opinion: You'll see the beam cutting through the darkness.

Latter opinion: You'll just see a spot on the screen where the beam hits.

Experience has shown that the former opinion is very common among pupils in the lower secondary school age range. Make sure to bring it out into the open, so that it gets effectively challenged. It's not enough to simply show the process and assume the learning will be automatic.

Now switch on the laser (with appropriate theatrical build-up). Nothing seems to happen. A red spot appears on the screen at the side of the room, but the laser beam itself can't be seen.

The big question is: Why can't we see the laser beam? (Because none of the laser light is entering our eyes). This can lead to an interesting discussion of situations where it is possible to see beams of light cutting through the air. Pupils may well refer to laser shows at pop concerts, the projection lights in cinemas, car headlamps on a foggy night. In each of these cases there is something which will scatter the light into our eyes.

An interesting follow-up question is: How come we can see the red spot on the screen? (Here laser light is being reflected in all directions from the wall and some travels to our eyes).

Use chalk dust from the board rubber (if you still use one) or a fine powder such as talc, or alternatively a fine water spray to scatter the beam. The room light is off and the effect is stunning as the beam becomes visible as light is scattered away from it.

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Totally in the dark!

Reflection
Light, Sound and Waves

Totally in the dark!

Classroom Activity for 5-11 11-14

What the Activity is for

Experiencing a completely dark space.

This activity allows pupils to enter a completely dark space, something which very few are likely to have previously experienced. Once in this light-free space they will recognise that it is impossible to see anything around them.

What to Prepare

This activity depends on the availability of a light-tight space. If your school has a photography dark room that will be perfect for this activity. If not, a handy store cupboard (partially cleared out for the occasion!) will serve just as well.

What Happens During this Activity

This is a great lesson! The impact of the activity is much enhanced by the discussion between teacher and pupils which leads up to the dark room experience. The starting point is: How are we able to see the things around us? This can lead on to talk about places where the pupils are unable to see anything. Typically pupils will refer to being outside at night or perhaps to the moment when you first switch off your bedroom light and it's completely black. In either case, however, pupils will be happy to tell you that after a bit your eyes get used to the darkness and you can see the things around you in the bedroom.

The discussion can be pushed further by introducing what you might call the: Hand in front of your nose test.

The challenge is: Can you think of a place where it is so dark that you cannot see your hand in front of your nose?

Maybe some pupils will have been potholing or caving and it will be good to listen to their experiences. You might refer to mining accidents where miners have been trapped underground, without light waiting for their rescuers in complete darkness. You might also ask the question of whether Superman would be able to see in the dark, with the special rays coming from his eyes.

To carry out the hand in front of your nose test pupils can go into the dark room in groups of four.

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Introducing light sources and shadows

Reflection
Light, Sound and Waves

Introducing light sources and shadows

Classroom Activity for 5-11

What the Activity is for

This activity focuses on the idea that light travels in straight lines and this behaviour causes shadows.

What to Prepare

  • several pieces of cardboard of different shapes
  • a torch
  • a screen or plain wall

What Happens During this Activity

Start with a piece of cardboard – shine a torch at the cardboard and ask the children to look what happens on the wall, and between the cardboard and the wall.

Questions to investigate:

Teacher: Does the size of the shadow depend upon where the torch shines from?

Teacher: How dark is the shadow? Is it the same darkness everywhere behind the card?

Teacher: What happens if you make a hole in the card?

A possible extension that links with the next episode is to place a stick in the ground outside. Ask children to record the length of the stick's shadow at the same time of day, on different days of the year.

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Tracking Brightness

Reflection
Light, Sound and Waves

Tracking Brightness

Classroom Activity for 5-11

What the Activity is for

A story told with a data logger.

This emphasises the graph as a story about something and a way of communicating. It is an opportunity to increase children's familiarity with dataloggers.

What to Prepare

  • portable dataloggers with light sensors (You'll ideally need a number of portable dataloggers with the ability to see what you have captured, fitted with sensors and rigged to measure brightness in arbitrary units. Failing this you can record the light using any such device, then feed it into display unit, such as a desktop computer, later.)

What Happens During this Activity

Challenge the class to find an event where the light level varies in an interesting way.

They should record the light from this event, then tell the story of one aspect of the lightscape using a graph.

They should be allowed full access to graphical analysis and annotation tools, so that the computer does more than plot the graph. The final product should tell an interesting story.

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In straight lines

Reflection
Light, Sound and Waves

In straight lines

Classroom Activity for 5-11 11-14

What the Activity is for

This is a teacher demonstration activity to show that light travels in straight lines.

What to Prepare

  • a bright light source. Use some kind of point source (where the light comes from a relatively small aperture) to produce a well defined shadow on the screen
  • a table tennis ball (or some other smooth-surfaced ball) hung from a piece of cotton (super-glue the cotton to the ball)
  • a screen

What Happens During this Activity

Hang the ball from a metre rule and hold it in the beam of light between the light source and the screen. With a good black-out for the room and a strong point source of light, a striking shadow will be produced on the screen.

Draw the children's attention to the sharpness of the shadow, how clean the line is between light and no light. Also, make the point that the shape of the shadow, although bigger, is exactly the same as the shape of the ball. This leads to the idea that the light must be travelling in straight lines to create such a shadow on the screen. The notion of light travelling in straight lines may seem obvious to many of the children. You might wish to explore an imaginary scenario which involves the light from the source bending around the ball. What would the shadow on the screen look like then?

Ask the children to predict what will happen to the shape and size of the shadow on the screen, if the ball is moved closer to, and further from, the screen.

In developing these ideas, you are likely to find yourself sketching out ray diagrams for the children.

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Mirror writing

Reflection
Light, Sound and Waves

Mirror writing - a reinforcement activity

Classroom Activity for 5-11

What the Activity is for

Developing the vocabulary used to describe light in a new and challenging context.

Children will have started to describe lights and come to some common agreement which allows them to communicate with each other. They will also have begun to think about the sources of those lights, both what is luminous and the quality of light those luminous objects give rise to. This is a chance to challenge and extend this evolving descriptive framework.

So this is a useful extension or reinforcement activity.

What to Prepare

  • Some cheap plastic mirrors
  • Pencils
  • Paper

What Happens During this Activity

Children are asked to write their names on pieces of paper in such a way that when viewed in the mirror the writing appears normal.

This is an excellent activity for a 5 minutes class mat time or small group work. Both these can be run either by an adult or by a child. The evolving ideas and the reasoning are the target, rather than the final decision.

Teacher Tip: It is a good idea to have a good means of revealing the source to avoid frustration. Even if when the writing still comes out backwards, there can be some learning taking place. This is not an activity to award right and wrong badges.

You can smooth the path by asking:

Teacher: Which letters did you find most easy to mirror write with?

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