Unit #: Day #: (Title)
|Unit #3, Lesson #6 |SNC 2D, Grade |
| |10 |
| |Learning Goals |Materials |
|75 min |-Mirrors Concave & Convex |Textbook |
| |-Concave mirror properties |Handouts |
| |-Ray diagrams with concave mirrors |Homework Sheets|
| |-Mirror and magnification equations. Use predictions to compare to experiment. | |
| |Whole Class (Discussion | |
| |1)Diverging Mirror Images | |
| |Diverging (Convex) Mirrors Presentation | |
| |On an overhead explain finding images using diverging mirror rules, using a ray diagram and the four types of | |
| |incident rays. | |
| |Give students about 15 min to work on the two scenarios on their handouts. | |
| | | |
| |2) Mirror/Magnification Equations | |
| |You can predict the characteristics of an image using two equations: the mirror equation and the magnification | |
| |equation. | |
| |The mirror equation allows you to calculate the location of the image and the magnification equation allows you to | |
| |calculate the size or height of the image relative to the object | |
| |Go over example 1. Give students example 2-3 and take up after a while. | |
|Minds On… | | |
|20 MIN | | |
| |Individual(Worksheet | |
| |-Complete lesson6 worksheet | |
| |-Images with diverging mirrors & using the mirror/magnification equation | |
|Action! | | |
|40 MIN | | |
| |Individual(Checkout Problem | |
| |On a piece of paper have the students work out their solution to the following problem: A concave mirror has a focal| |
| |length of 12 cm. An object with a height of 2.5 cm is placed 40 cm. from the mirror. A) calculate the image | |
| |distance (17.12 cm), b) Calculate the image height (-1.07 cm). | |
|Consolidate | | |
|Debrief | | |
|15 MIN | | |
| |Home Activity or Further Classroom Consolidation | |
| |Homework: Complete Lesson6 Homework sheets to be handed in for marks! | |
Convex (Diverging) Mirrors
Label the diagram and Define the following in your own words:
Centre of Curvature:
Principal Axis:
Vertex:
Focus/(Focal Point):
Focal Length:
Draw/label the following paths on your diagram that light rays can take as they pass through different points and strike the diverging/convex mirror.
1) An incident light ray parallel to the principal axis reflects out as though coming from the focus
2) A light ray that heads toward the centre of curvature is reflected back onto itself.
3) An incident ray apparently directed at the focus will reflect parallel to the principal axis.
4) A ray aimed at the vertex will follow the law of reflection.
Convex (Diverging Mirrors)
Rays are reflected and diverge, giving the illusion that the rays originated inside the mirror.
Diverging mirrors always produce virtual images that are smaller than the object.
Ray Diagrams for Convex Mirrors
Locate the image for each convex mirror
|Observations |
|S | |
|A | |
|L | |
|T | |
|Observations |
|S | |
|A | |
|L | |
|T | |
These scenarios summarize the characteristics of ALL images in diverging (convex) mirrors. The image will always be smaller than the actual object and the image increases in size when the object is moved closer to the mirror.
Calculations for Curved Mirrors
The curved mirror equation: [pic]
where [pic] is the object distance, [pic] is the image distance, and [pic] is the focal length.
Magnification Formula: [pic] or [pic]
which leads to [pic]
where [pic] is the height of the image and [pic] is the height of the object.
In optics, the negative sign is used to indicate virtual distances (image and focal point) and inverted heights. Based on the values and information given, you will likely need to insert the negative sign yourself.
Example – A concave mirror with a 20 cm focal length has a candle placed in front of it 30 cm from the vertex. Find the image position and the magnification for this situation.
Given: [pic] [pic] [pic]
[pic]
Answer the following:
1) A concave mirror has a focal length of 12 cm. An object f height 2.5 cm is placed 40 cm in front of the mirror.
a) Draw a diagram describing the setup.
b) Calculate the image distance.
c) Calculate the image height.
2) A dancer is applying make-up with a concave mirror. She is 35 cm in front of the mirror and the image size is 72 cm behind the mirror.
a) Draw a diagram describing the setup.
b) Use the mirror equation to calculate the focal length of the mirror.
-----------------------
[pic]
|Incident Ray |Reflected Ray |
|Parallel to principal axis |Reflects out as though coming |
| |from focus |
|Directed at focus |Reflects back parallel to |
| |principal axis |
|Directed at centre of curvature |Reflects straight back on itself |
|To vertex |Point acts like plane mirror |
| |[pic] |
C
F
C
F
C
F
C
F
[pic]
[pic]
C
F
C
F
f is negative
diverging
[pic] is negative
mirror
yes
[pic] is negative
Is object inside f?
converging
When is the image inverted?
NO
[pic] is positive
[pic]
Image distance is positive so image is real
Magnification is negative so image is inverted
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