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Reflected light

How do light rays from a book and other such (non-luminous) objects reach our eye?

Light from the lamp or another light source strikes the book and some of the light is reflected into our eye.

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Reflection : Good or Poor?

Objects which reflect light well have smooth, shiny surfaces and are usuallypale colours.

They give clear images because they reflect the light regularly.

Mirrors are excellent reflectors.

Objects which do not reflect light well have rough, matt surfaces and are usually darkcolours.

They give no or diffuse images because they reflect the light irregularly.

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Reflection : Good or Poor?

Arrange these items along the arrow:

White Paper

Red

Roses

Polished Black Shoes

Al foil

Yellow

Banana

Blue Car

Tree Bark

Tangerine

Green Leaf

Tarmac Road

Best Reflectors

Worst Reflectors

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What happens to the light which isn’t reflected?

• Some of this light may be absorbed (e.g. as heat).

• Some of this may also be transmitted (e.g glass reflects a small amount of light, absorbs some of the rest and allows most of it to pass through.

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Reflection: Investigating Reflection.

These activities allow you to investigate the main laws of reflection.

You should summarise each investigation with a law you have written based on that exercise.

1) Reading in mirrors.

2) How far away is the image?

3) The maths of reflection.

4) Reflecting without mirrors.

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Reflection: 1. Reading in Mirrors.

In small groups, take it in turns to read the list of words on the next slide with your back to the screen using a mirror.

You can only move on to the next word when you read the first word correctly.

Put your results in a table like this:

Name Time taken to read [s]

Natasha 46

Pashmina 56

David 85

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Reflection : 1. Words

Dog Man Ball

Bat Bike Ants

Park Fins Pink

Litter Sandy Shark

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Reflection : 1. Results

A) Who read the words in the quickest time?

B) Plot a bar chart of you r results like:

C) What was the average time taken in your group?

A graph showing the results of 'Reading in Mirrors'

0

50

100

Natasha Pashmina David

Name

Tim

e ta

ken

[s

]

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Reflection : 1. Lateral inversion

The way plane mirrors reflect light regularly gives a clear image which is the same size as the object

- but what is different about the image ?

This is called lateral inversion.

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Reflection : 2. How far away is the image?

1. Fix a plane mirror along the centre of a

piece of A4 paper and draw around it.

Place a pin as the object in front of the

mirror.

2. Line up a ruler with the image of the pin and draw along the

edge of the ruler on the paper. Repeat for 3 more positions of

the ruler.

3. Remove the mirror and ruler. Where the lines cross is the

image position. What are the distances between the mirror and

object and its image?

I

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Reflection : 3. The Maths of Reflection

Fix a plane mirror to a piece of A5 paper and draw around it.

Angle ofI ncidence [i]

Angle ofReflection [r]

Angle i

Angle r

Draw a normal line (at 90º) through the middle of the mirror outline.

Use a ray box to shine an incident ray at the mirror - plot the incident and reflected rays.

Measure the angles of incidence [i] and reflection [r] and write the answers in the table on the right.

Repeat for another 5 angles of incidence.

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Reflection : 4. Reflecting without mirrors

Mirrors are good reflectors but not perfect - they give 2 reflections.

We use glass prisms instead of mirrors in good quality binoculars and other instruments.

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Reflection : 4. Reflecting without mirrors

Shine rays of light into a prism as shown in the ray diagrams below.

Copy and complete the ray diagrams using a ruler and pencil.

Don’t forget to include arrows on your rays!

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Using plane mirrors

By positioning two plane mirrors at 45° to each other at either end of a tube we can make a _________.periscope

Periscopes are used in _________.submarines

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Reflection : Summary

You should now know that :

Pale and shiny surfaces are good reflectors, dark and rough surfaces are not.

The image in a plane mirror is laterally inverted.

The image is the same distance behind the mirror as the object is in front.

The image in a plane mirror is the same size as the object.

angle of incidence = angle of reflection

¡ = r