Optics Lesson 3Introduction to Reflection and

Plane Mirrors

Terminology of Reflection

• Perpendicular

• Parallel

Terminology of Reflection

Terminology of Reflection

• Plane Mirror (Flat Mirror)

• Concave Mirror (caved inwards)

• Convex Mirror (bumped out towards you)

Reflection

The law of reflection – The angle of incidence is equal to the angle of reflection

Each arrow represents a “ray” of light.

Angle of Incidence

Angle of Reflection

Note: The angles are not measured to the edge They are measured to the “normal”

The normal is a doted line that is drawn perpendicular to the mirror.

Reflection from a mirror

Incident ray

Normal

Reflected ray

Angle of incidence Angle of reflection

Mirror

• The Law of ReflectionThe Law of Reflection

Angle of incidence = Angle of reflectionAngle of incidence = Angle of reflection

In other words, light gets reflected from a surface at the same angle it hits it.

The same !!!

Types of Reflection

• Clear Reflection:– Reflection of light off a smooth surface

• Diffuse Reflection: – Reflection of light off an irregular survafe

Clear vs. Diffuse Reflection

• Smooth, shiny surfaces have a clear reflection:

Rough, dull surfaces have a diffuse reflection.

Diffuse reflection is when light is scattered in different directions

• Clear Reflection

• Diffuse Reflection

Ray Diagrams

A ray diagram is a method used to determine where an image will appear when an object is viewed through a mirror or lens

A light ray radiates rays in millions of directions but we are only concerned with the ones that reach our eyes

Locating an Image in a Mirror• Since we know light travels

in a straight line our brains think that the source is actually behind the mirror

• This is called a virtual because the image location we perceive is not real

• Note, dashed lines indicate light rays behind the mirror

• We can use light rays and the laws of reflection to determine where our object is located and draw it. We do this using object-image lines

• Rules for object-image lines1)The distance between the object and mirror =

the distance between the mirror and image2)The object-image line is perpendicular to the

mirror surface

• By choosing enough points we can accurately locate and draw our virtual image

The Result - Lateral Inversion• The orientation of an image in a plane

mirror is flipped horizontally and in reverse order Try it for your self

L

Lateral Inversion

Ambulance

- Why do you think they paint it backwards?

SCIENCE!

SALT• When you describe the properties of an image,

you need to examine four characteristics

1)Size of image (compared to the object: same size, smaller, larger)

2)Attitude of image (which way the image is orientated compared to the object: upright or inverted)

3)Location of image (distance from mirror)

4)T ype of image (real or virtual)

SALT

• An image in a plane mirror is ALWAYS the same size as the object, upright, equal distance behind the mirror virtual (behind the mirror)