# Reflection 3.2 (a) Reflection of light Core

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Reflection 3.2 (a) Reflection of light Core
• Describe the formation, and give the characteristics, of an optical image by a plane mirror • Use the law angle of incidence = angle of reflection Supplement • 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?
There are two ways we see objects….. Do we see all objects in the same way? We see some objects because they are light sources. We see some objects by reflected light.

Objects seen by reflected light
Seeing objects Light sources Objects seen by reflected light Sun Jupiter Firefly Moon Light bulb Book Light bulb Sun Jupiter Book Firefly Moon

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.

There are two types of m____. F__ mirrors and c____ mirrors.
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 lat urved lane oncave onvex

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.

Ambulance Ambulance Rear-view mirrors
Imagine you are driving along in your car…… Ambulance …and then you look up and see the following in your mirror….. Ambulance …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:

Dog Man Ball Bat Bike Ants Park Fins Pink Litter Sandy Shark
Words Dog Man Ball Bat Bike Ants Park Fins Pink Litter Sandy Shark No Cheating

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?

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? Image Object 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 pack Ray box Slit Concave mirror Protractor Ruler 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 Incident angle i Incident ray 4. Draw a tangent to the mirror where the ray hits. Reflected angle r 5. Draw a normal to the mirror (at right angles to the previous line). Reflected ray 6. Measure the incident angles and the reflected angles for each ray. Record your results in a table.

Angle of incidence = Angle of reflection
Results i/° r/° 30 45 70 85 30 45 70 85 Angle of incidence = Angle of reflection What do you notice? Is there a pattern?

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?
The Sun A star Traffic lights A book

Which of the following is not seen by reflected light?
Your hand Jupiter Light bulb The Moon

Which of the following is the most opaque?
Milk Sea water Air Drinking water

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

Which statement below is untrue for the image in a plane mirror?
It is laterally inverted It is real It is same size as the object 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.

as far behind the mirror as the object is in front,
= What I should know: The law of reflection: the angle = the angle of 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.