10 cool ideas for teaching reflection of light

Different approaches for teaching the reflection of light -Specular vs diffuse Reflection

These ideas are from the Institute of Physics 2014 PIPER conference check out the twitter conversations on #PIPER14. These ideas are stolen from a workshop that combined Institute of Physics TLCs (Teaching and Learning Coaches) and PNCs (Physics Network Coordinators)

When I was teaching I probably wouldn’t have bothered reading this, but please do as it has some great ideas in it.

 

Easy to teach right?

The only diagrams you need are the ones below

 

lesson2
However, can your students answer these questions?

If you shine a laser onto the ceiling everyone in the room can see it – why? (diffuse reflection)
If you shine the laser onto a mirror so it reflects onto the ceiling will you be able to see the beam on the mirror? (No!)
What about shining a laser onto a TV screen, tablet, phone, projector screen. Will the intensity you see the reflection vary depending on the angle?

If you shine a laser onto the image produced by a mirage creator or the horrendously misnamed science museums hologram creator, what would you see?

 

mir100_3

 

(This blew my mind! The spot of the laser illuminates the image of the pig! )

 

Prelude to the lesson

A fun and engaging activity not so much for improving their physics, but I like them to have something to take home that shows how physics is cool.

Print out or have students draw two stars, one inside the other – There is a worksheet here but please draw attention to the horrific laser eyes ray diagram !!
http://students.washington.edu/nbout/LessonPlans/mirrordrawing.pdf

The setup is as shown below or simply have them hold the mirror up above their eyes

PB_practice-makes-perfect-mirror-drawing-set-up-500

 

What else do we need to know before we teach this?

Light travels in straight lines – what’s the evidence?

Pinhole cameras – lots of fun but you must decide what learning takes place . These are great for ‘What happens if…? ‘ type questions.

What might happen if:

The pinhole becomes bigger/smaller/multiple …
The camera becomes shorter/longer/wider …
The image is nearer/further/bigger/smaller ……

Let them loose to come up with ideas and explore!

23 Pinhole cameras to build yourself here

Shadow puppets

A nice one to do with a cross curricular project with art where they can make shadow puppets or explore reflection of light with colours.

What might happen if …..

The puppet is moved closer to /further from the light source/the screen

alternatively learn some of these

hand-shadow-puppets

 

Laws of reflection

A video to start with can be this kitten. What may it be noticing about the laws of reflection?

 

Selfies

An interesting one is to look at the front facing camera of a phone which laterally inverts the image while you set it up. This enables you to turn the phone the same way you would a mirror. The image itself when taken is the right way round – hence it looks weird! get them to write selfie on a post-it note and stick it on their forehead. It will look laterally inverted when they look at the phone, but when they take the picture it is the right way round. Get them to discuss – why do they do that?
Reflections in a mirror

Give them a mirror and get them to work out the laws and what misconceptions people may have, then ask the question – why is the image laterally inverted, but not upside down?

 

Maths cross curricular ideas

Put two mirrors together with an object in front of them on a sheet with a protractor on it (or printed) as shown in the diagram. What is the relationship between the angle between the mirrors and the number of images seen?
There are some good examples here http://www.schoolphysics.co.uk/age16-19/Optics/Reflection/text/Reflection_/index.html

Angles60deg

 

 

Estimate the height of a tall tree.

There are several different ways to do this outlined here or here

http://www.schoolphysics.co.uk/age16-19/Optics/Reflection/text/Reflection_/index.html

Problem solving using similar triangles and a mirror
You are given a mirror and a metre rule. Calculate the height of a tall object

 

ST09-006W-833051
Real life problem – the Walkie Talkie building that melted a car!

Read the news articles here and here

ScorchieBo_660

What could you do?
What did they do?
Finally a crazy idea which I take credit but not responsibility for

Lighting a fire with a coke can. I ran this lesson a few times massively successfully but the risks are significant so please risk assess and check your school is happy for you to do it.
Students are given a coke can, cocktail sticks , tape, a kitkat bar, paper, coloured pens, a clamp etc and told to light a fire!

Full instructions here

Cokecan1702

http://www.wildwoodsurvival.com/survival/fire/cokeandchocolatebar/

 

 

Please feel free to add any more ideas in the comments section

3 thoughts on “10 cool ideas for teaching reflection of light

  1. I like to surprise students by showing them that sugar crystals are really transparent, not white. (The same applies to snowflakes, talcum powder, etc.) I can prove it to them by sprinkling a few sugar crystals on a piece of colored paper, then shining a light on the paper from underneath. If the students look closely, they can see the colored paper through the crystals. This leads to a discussion of how even transparent objects still reflect a little bit light at every surface, and how the collective effect of many small reflections makes a cup of sugar appear white even though the individual crystals aren’t.

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