© Boardworks Ltd 2003 Reflection 3.2 (a) Reflection of light Core Describe the formation, and give...

© Boardworks Ltd 2003

Reflection3.2 (a) Reflection of lightCore• Describe the formation, and give the characteristics, of an optical image by a plane mirror• Use the law angle of incidence = angle of reflectionSupplement• Perform simple constructions, measurements and calculations


Objectives

Recall that light travels in straight lines.

Draw accurate ray diagrams.

Describe how we see objects.

Define the words opaque and transparent.

Describe the images formed in a plane mirror.

Recall how the angle of incidence and angle of reflection are related for a plane mirror.

Describe the differences between convex and concave mirrors.


Light rays

A light ray is a narrow beam of light. When drawing light diagrams always…..

1. Use a ruler.

2. Add an arrow to show the direction the light ray is travelling in.


How does light travel?

1) Fill a clear glass trough or empty fish tank with smoke.

2) Shine rays of light through the tank and describe what you see.


Light travels in straight lines

Your experiment shows that light travels in straight lines.

What every day consequences do you think this fact has?

You can not see around corners.

Shadows are formed in the area behind an object where light can not reach.


Seeing objects

How do we see an object?

Do we see all objects in the same way?

There are two ways we see objects…..

We see some objects because they are light sources.

We see some objects by reflected light.


Seeing objects

Light sources Objects seen by reflected light

Sun

Sun

Jupiter

Jupiter

Firefly

Firefly

Moon

Moon

Book

Book

Light bulb

Light bulb


Light sources

How do light rays from the Sun and other light sources reach our eye?

They travel in a straight line directly into our eye.


Reflected light

How do light rays from a book and other such objects reach our eye?

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


Opaque and transparent materials

Use a textbook or other source to find out what the words opaque and transparent mean.

Opaque materials do not let light though.

Transparent materials do let light through.


Reflections

There are two types of m____. F__ mirrors and c____ mirrors.

Flat mirrors are known as p___ mirrors.

If a mirror curves in then it is a c_____ mirror, if it curves out it is a c____ mirror.

irrors laturved

lane

oncaveonvex


Plane mirrors

Write out the letters of the alphabet down one side of a piece of paper, then next to the letter draw what the letter would look like as seen in a mirror.

What do you predict the letter ‘L’ would look like in a mirror?

What do you predict the letter ‘P’ would look like in a mirror?


Right and left

What happens to writing in a mirror?

The writing in a mirror is laterally inverted or back to front.

If you are wearing a T-shirt with some writing on and wave your right hand what will your image appear like in a mirror?

The writing on your T-shirt will be back to front and your image will be waving it’s left hand.


Rear-view mirrors

Imagine you are driving along in your car……

…and then you look up and see the following in your mirror…..

…with your knowledge of mirrors how must the writing be written on the vehicle?


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


Words

Dog Man Ball

Bat Bike Ants

Park Fins Pink

Litter Sandy Shark


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

]


Image size and distance

For a plane mirror how does the size of the image and the image distance from the mirror relate to the original object?

Object Image

Image size and object size are the same.

The image distance is the same as the object distance from the mirror.


Investigating reflection

Apparatus:

Power packRay boxSlitConcave mirrorProtractorRuler

The ray box

will get very

hot, be careful

when handling it.


Investigating reflection

1. Place the concave mirror on a piece of paper.

2. Draw a line along the front of the mirror.

3. Shine rays of light at varying angles to the normal and record the position of the incident and reflected rays

6. Measure the incident angles and the reflected angles for each ray. Record your results in a table.

Incident angle i

Reflected angle r

Reflected ray

Incident ray

4. Draw a tangent to the mirror where the ray hits.

5. Draw a normal to the mirror (at right angles to the previous line).


Results

i/° r/°030457085

0

30

4570

85

What do you notice? Is there a pattern?

Angle of incidence = Angle of reflection


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


Reflection : Curved mirrors

Concave reflectors are used to focus signals from distant satellites.

Convex reflectors are used to widen the field of view.


Which of the following is not a light source?

A. The Sun

B. A star

C. Traffic lights

D. A book


Which of the following is not seen by reflected light?

A. Your hand

B. Jupiter

C. Light bulb

D. The Moon


Which of the following is the most opaque?

A. Milk

B. Sea water

C. Air

D. Drinking water


What do we call the area behind an object where light can not reach?

A. Transparent

B. Shadow

C. Opaque

D. Outline


Which statement below is untrue for the image in a plane mirror?

A. It is laterally inverted

B. It is real

C. It is same size as the object

D. It is the same distance from the mirror as

the object


Objectives

Recall that light travels in straight lines.

Draw accurate ray diagrams.

Describe how we see objects.

Define the words opaque and transparent.

Describe the images formed in a plane mirror.

Recall how the angle of incidence and angle of reflection are related for a plane mirror.


=

What I should know:

The law of reflection:the angle = the angleof incidence of reflection

A periscope uses 2 mirrors, set at 45° to the horizontal.

The image in a plane mirror is:

as far behind the mirror as the object is in front,the line joining the image to the object is at 90° to the mirror,a virtual image (no light rays go through it),the same size as the object,laterally inverted.

What I should be able to do:

Carry out an experiment to test the law of reflection.

Draw a diagram of a periscope and explain how it works.

Describe an experiment to find out the position of an image in a plane mirror.

Understand a ray diagram which shows 2 light rays reflected off a mirror and into an eye.

© Boardworks Ltd 2003 Reflection 3.2 (a) Reflection of light Core Describe the formation, and give...

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