Optics Lesson 3 Introduction to Reflection and Plane Mirrors
Introduction to Reflection and Plane Mirrors
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Transcript of Introduction to Reflection and Plane Mirrors
Introduction to Reflection and Plane
Mirrors- Terminology of Reflection- Reflection from a mirror- The Law of Reflection- Types of Reflection- Ray Diagrams- Locating an Image in a Mirror- Lateral Inversion- Properties of an image
Terminology of Reflection
• Perpendicular
• Parallel
Recall - Terminology
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 Reflection
Angle 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 (Specular) Reflection:– Reflection of light off a smooth surface
• Diffuse Reflection: – Refection of light off an irregular surface
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 DiagramsA 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 image 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) Type 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)