Reflections in a Plane Mirror
Geometric Optics
 The use of light rays to determine the path of
light when it strikes an object
 Incident light: light ...
Matter Classified by
behaviour when light strikes
Matter

Transparent

Translucent

Opaque

Effect on
incident light

Tran...
Ray Model of Light
 Light rays
 illustrate the travel
of light in a straight
line
 arrows show the
source of the light
...
Ray Diagram Terminology

 Incident ray – incoming ray that strikes a surface
 Reflected ray – ray that bounces off a ref...
Ray Diagram Terminology
 Angle of incidence –
angle between the
incident ray and the
normal
 Angle of reflection –
angle...
Lab: Reflecting light off a plane
mirror
 Nelson Science Perspective 10 textbook
section 11.5 page 482-483
 Work in grou...
Reflection Terminology
 Reflection: bouncing back of light from a
surface
 Mirror: any polished surface that exhibits
re...
Types of Mirrors

 Plane mirror: flat
 Curved mirror
a. Concave / converging
b. Convex / diverging
Optics Symbol
Actual Mirror

Scientific Mirror Symbol
Reflective
surface

Glass

Opaque
side
Thin
reflective
surface
Reflection in a Plane Mirror
Law of Reflection
 When light reflects off a surface, the angle of
incidence is always equal to the angle of
reflection

...
Reflection in a Plane Mirror
Law of Reflection
 The incident ray, the reflected ray and the
normal all lie in the same plane.
Types of Reflection
SPECULAR REFLECTION
Reflection off a
smooth surface
DIFFUSE REFLECTION
Reflection off an
irregular/dul...
Reflection Terminology
 Reflection: bouncing back of light from a
surface
 Mirror: any polished surface that exhibits
re...
Brain and the plane mirror
1.

Eyes detect reflected
light from a plane
mirror

2.

Brain projects light
rays backwards in...
Brain and the plane mirror
Result:
Result:
•brain thinks there is a light
•brain thinks there is a light
source behind the...
Brain and the plane mirror
Properties of an image
Attitude

Type
Real

Size

Virtual

Enlarged
Reduced

Upright

Inverted
(vertical)
Laterally
Invert...
Type
 Real - image appears
in front of the mirror
(could be projected
onto a screen)
 Virtual - image
appears behind the...
Virtual
image
Size
 Enlarged - image is larger than the object
 Reduced - image is smaller than the object
 Same - image is the same ...
Attitude
Upright

Inverted
(vertical)

Laterally
Inverted

image is
right-side up

image is
upside-down

image is flipped
...
Lateral Inversion
Summary of Properties of an
Image Using S.A.L.T.
Size

Attitude

Location

Type

Larger, same, or smaller

Upright or inve...
Lab: Locating Images in a
Plane Mirror
 See workbook
Locating an image in a plane
mirror
 A. Using Object-Image Lines
 B. Using Light Rays (ray diagram)
 C. Using both Obje...
Object distance = Image
Distance
Using object-image lines to locate
image in a plane mirror

Solid lines

Dashed lines of the same length
Locating an image in a plane
mirror
 A. Using Object-Image Lines
 B. Using Light Rays (ray diagram)
 C. Using both Obje...
Using light rays to locate image in
a plane mirror: Step 1
 Identify the top
and the bottom of
the object (label
these “A...
Using light rays to locate image in
a plane mirror: Step 2
 Draw an incident ray
(starting at point A)
 Draw a “normal” ...
Using light rays to locate image in
a plane mirror: Step 3
 Repeat step 2 with a
second incident ray at a
different angle...
Using light rays to locate image in
a plane mirror: Step 4

 Extend both
reflected rays behind
the mirror until they
inte...
Using light rays to locate image in
a plane mirror: Step 5
 Repeat steps 2-4
for Point B
 Draw the virtual
image using
p...
Locating an Image in a Plane
Mirror (Light rays)
1. Pick two points on the object (opposite sides)
2. Draw 2 incident rays...
Locating an image in a plane
mirror
 A. Using Object-Image Lines
 B. Using Light Rays (ray diagram)
 C. Using both Obje...
Using object-image lines and light
rays to locate image in a plane mirror:
Step 1
 Identify the top
and the bottom
of the...
Using object-image lines and light
rays to locate image in a plane mirror:
Step 2
 Draw a line from
point A that is
perpe...
Using object-image lines and light
rays to locate image in a plane mirror:
Step 3
 Draw an incident ray
(starting at poin...
Using object-image lines and light
rays to locate image in a plane mirror:
Step 4
 Extend line A to
point Ai
(equidistant...
Using object-image lines and light
rays to locate image in a plane mirror:
Step 5
 Repeat steps
2-4 for Point B
 Draw th...
Properties of an image in a plane
mirror
 S: Same size
 A: Upright
 L: Behind the mirror at the same distance that
the ...
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Reflections in a plane mirror

  1. 1. Reflections in a Plane Mirror
  2. 2. Geometric Optics  The use of light rays to determine the path of light when it strikes an object  Incident light: light from a source (e.g. bulb, sun) that strikes an object
  3. 3. Matter Classified by behaviour when light strikes Matter Transparent Translucent Opaque Effect on incident light Transmits Transmits some Absorbs or reflects Effect on visibility See through not clear Can not see through Example
  4. 4. Ray Model of Light  Light rays  illustrate the travel of light in a straight line  arrows show the source of the light and the direction of light travel
  5. 5. Ray Diagram Terminology  Incident ray – incoming ray that strikes a surface  Reflected ray – ray that bounces off a reflective surface  Normal – perpendicular line to a mirror surface
  6. 6. Ray Diagram Terminology  Angle of incidence – angle between the incident ray and the normal  Angle of reflection – angle between the reflected ray and the normal
  7. 7. Lab: Reflecting light off a plane mirror  Nelson Science Perspective 10 textbook section 11.5 page 482-483  Work in groups of 3  For each group hand in:  Light ray diagram  Observation chart  Answer to all questions on page 483
  8. 8. Reflection Terminology  Reflection: bouncing back of light from a surface  Mirror: any polished surface that exhibits reflection
  9. 9. Types of Mirrors  Plane mirror: flat  Curved mirror a. Concave / converging b. Convex / diverging
  10. 10. Optics Symbol Actual Mirror Scientific Mirror Symbol Reflective surface Glass Opaque side Thin reflective surface
  11. 11. Reflection in a Plane Mirror
  12. 12. Law of Reflection  When light reflects off a surface, the angle of incidence is always equal to the angle of reflection ∠i = ∠r
  13. 13. Reflection in a Plane Mirror
  14. 14. Law of Reflection  The incident ray, the reflected ray and the normal all lie in the same plane.
  15. 15. Types of Reflection SPECULAR REFLECTION Reflection off a smooth surface DIFFUSE REFLECTION Reflection off an irregular/dull surface
  16. 16. Reflection Terminology  Reflection: bouncing back of light from a surface  Mirror: any polished surface that exhibits reflection  Image: a reproduction of an original object through the use of light  Virtual image: an image formed by light that does not come from the image location (but it appears to come from the image)
  17. 17. Brain and the plane mirror 1. Eyes detect reflected light from a plane mirror 2. Brain projects light rays backwards in a straight line.
  18. 18. Brain and the plane mirror Result: Result: •brain thinks there is a light •brain thinks there is a light source behind the mirror source behind the mirror where where the light rays originate the light rays originate •see an image behind the •see an image behind the mirror called a virtual image mirror called a virtual image
  19. 19. Brain and the plane mirror
  20. 20. Properties of an image Attitude Type Real Size Virtual Enlarged Reduced Upright Inverted (vertical) Laterally Inverted Same
  21. 21. Type  Real - image appears in front of the mirror (could be projected onto a screen)  Virtual - image appears behind the mirror
  22. 22. Virtual image
  23. 23. Size  Enlarged - image is larger than the object  Reduced - image is smaller than the object  Same - image is the same size as the object a) b) c)
  24. 24. Attitude Upright Inverted (vertical) Laterally Inverted image is right-side up image is upside-down image is flipped horizontally
  25. 25. Lateral Inversion
  26. 26. Summary of Properties of an Image Using S.A.L.T. Size Attitude Location Type Larger, same, or smaller Upright or inverted Image distance Virtual or Real
  27. 27. Lab: Locating Images in a Plane Mirror  See workbook
  28. 28. Locating an image in a plane mirror  A. Using Object-Image Lines  B. Using Light Rays (ray diagram)  C. Using both Object-Image lines and Light Rays (ray diagram)
  29. 29. Object distance = Image Distance
  30. 30. Using object-image lines to locate image in a plane mirror Solid lines Dashed lines of the same length
  31. 31. Locating an image in a plane mirror  A. Using Object-Image Lines  B. Using Light Rays (ray diagram)  C. Using both Object-Image lines and Light Rays (ray diagram)
  32. 32. Using light rays to locate image in a plane mirror: Step 1  Identify the top and the bottom of the object (label these “A” and “B”)
  33. 33. Using light rays to locate image in a plane mirror: Step 2  Draw an incident ray (starting at point A)  Draw a “normal” where the incident ray hits the mirror  Use a protractor to draw a reflecting ray  (Remember that ∠i = ∠r )
  34. 34. Using light rays to locate image in a plane mirror: Step 3  Repeat step 2 with a second incident ray at a different angle  Draw an incident ray (starting at point A)  Draw a “normal” where the incident ray hits the mirror  Use a protractor to draw a reflecting ray  (Remember that ∠i = ∠r )
  35. 35. Using light rays to locate image in a plane mirror: Step 4  Extend both reflected rays behind the mirror until they intersect (Ai)
  36. 36. Using light rays to locate image in a plane mirror: Step 5  Repeat steps 2-4 for Point B  Draw the virtual image using points Ai and Bi as a guide
  37. 37. Locating an Image in a Plane Mirror (Light rays) 1. Pick two points on the object (opposite sides) 2. Draw 2 incident rays 3. Use the law of reflection to draw the reflected rays (draw normal, measure angle of incidence to determine angle of reflection) 4. Extend the reflected ray into the virtual side of the mirror (use dotted lines) 5. Find the intersection of the two extended reflected rays 6. Repeat for the second point 7. Using the 2 intersection points to draw the virtual image (dot the lines).
  38. 38. Locating an image in a plane mirror  A. Using Object-Image Lines  B. Using Light Rays (ray diagram)  C. Using both Object-Image lines and Light Rays (ray diagram)
  39. 39. Using object-image lines and light rays to locate image in a plane mirror: Step 1  Identify the top and the bottom of the object (label these “A” and “B”)
  40. 40. Using object-image lines and light rays to locate image in a plane mirror: Step 2  Draw a line from point A that is perpendicular to the mirror
  41. 41. Using object-image lines and light rays to locate image in a plane mirror: Step 3  Draw an incident ray (starting at point A)  Draw a “normal” where the incident ray hits the mirror  Use a protractor to draw a reflecting ray  (Remember that ∠i = ∠r )
  42. 42. Using object-image lines and light rays to locate image in a plane mirror: Step 4  Extend line A to point Ai (equidistant from point A on the other side of the mirror)  Connect point Ai to your reflection ray
  43. 43. Using object-image lines and light rays to locate image in a plane mirror: Step 5  Repeat steps 2-4 for Point B  Draw the virtual image using points Ai and Bi as a guide
  44. 44. Properties of an image in a plane mirror  S: Same size  A: Upright  L: Behind the mirror at the same distance that the object is in front of the mirror  T: Virtual image

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