Plane Mirror & Reflection

Normal – imaginary vertical line where the light strikes mirror

Angle of Incidence (θi) – the angle of the incident ray to the normal

Angle of Refection (θr) – the angle of the reflected ray to the normal.

Law of reflection – when light strikes a surface, θi = θr

Mirror(reflecting surface)

Reflecte

d RayIncident Ray

Normal

θrθi

LEFT- RIGHT REVERSAL

Da Vinci WritingMaterials: plane mirror, paper, pencil

Place the mirror on the paper and hold it there with your hand

While LOOKING into the mirror, try and print you name on the piece of paper so that it appears correctly IN THE MIRROR not on the page

You might need to practice.

Try it with your non-dominant hand

Try writing a secret message to a friend and have them de-code it

Check the accuracy of de-coding the message with the mirror

Specular ReflectionSpecular Reflection: reflection off of a

smooth, shiny surface. Reflected rays are all parallel to each other, and the image is clear.

Diffuse ReflectionDiffuse Reflection: reflection off of an irregular

or dull surface. Reflected rays are not parallel and the image is fuzzy.

←Specular

Diffuse ↓

DEMO!!Flash Light & Aluminum

Foil

Specular vs. Diffuse Specular vs. Diffuse ReflectionReflection

Applications of Specular and Diffuse Reflection:

•Countertop surfaces•Furniture or car wax•Glazed vs, unglazed ceramics•Matte vs. Glossy finish on photographs or in paint

Virtual ImageAn image formed by light coming from an

apparent light source; light is not coming from the actual image location

• Created using plane mirrors

Real ImageAn image that can be seen on a screen as a

result of light rays actually hitting (arriving) at the image location

Pig Demo

Describing an ImageWhen describing an image you need to

consider 4

characteristics known as SALT:

S= Size of image (compared to the object: same size, smaller or larger)

A= Attitude of image ( which way the image is oriented compared to the object: upright or inverted)

L= Location of image (infront or behind mirror or lens)

T= Type of image (real or virtual)

Size Attitude Location

Type

Image

Large Same Small

Upright or Inverted

In front or behind mirror

Virtual or real

An image in a plane mirror is always:

S= same size

A= Upright but backwards

L= Behind the mirror (same distance as object in front)

T= Virtual image

Creating an Image

How to find an Image?1. Draw the Plane mirror in correct location

2. Draw object on left side of the mirror

3. Draw a ray (incidence) through the object to the mirror and reflect the ray off the mirror

4. Change the angle and draw another ray through the object and reflect it off the mirror

5. Extend the Reflected rays “through” the mirror until the cross each other

6. Where the lines cross is where the object is located

Example 1 Simple

Creating Images

Locating Images in a Plane Mirror Lab

Purpose: to test the characteristics of an image in a plane mirror

Material: ray box paper plane mirror pencil ruler

Procedure: See Ms. Jamieson

Observations:

Locating Images in a Plane Mirror Lab

Arrow head (cm)

Arrow Tail (cm)

Length from Object to Mirror

Length from Image to mirror

Analysis:1.Using your observations describe (SALT) the image that appeared in the plane mirror?

2.What can you predict about all images in plane mirrors?

3.Is there a simpler way to locate the image in a plane mirror without using light rays?

Pla

ne

Mir

rors

Plane mirror worksheet

Applications of Plane Mirrors

1) Bathroom mirrors to see yourself

2) Rear View mirrors

3) Periscopes

Applications of Plane Mirrors

1) Cosmetic mirrors

2) Rear View mirrors

3) Periscopes

Can you write your name so it looks forward in the mirror?

Leonardo da Vinci used mirror writing when writing in his note book about his inventions. Can you write a mirror message to your neighbour?