Concave mirrors

1. Concave MirrorsConcave Mirrors
The laws remain the sameThe laws remain the same

2. The Sky Mirror in Monte CarloThe Sky Mirror in Monte Carlo

3. The Sky MirrorThe Sky Mirror
What do you What do you
notice about notice about
the mirror the mirror
image you image you
see?see?

4. Properties of Concave MirrorsProperties of Concave Mirrors
Concave mirrors are shaped curved like a Concave mirrors are shaped curved like a
letter C or the inside of a sphereletter C or the inside of a sphere
You can identify them from other mirrors You can identify them from other mirrors
because light goes into them like entering a because light goes into them like entering a
CAVECAVE
Examples: the side of spoon you put food on, Examples: the side of spoon you put food on,
a makeup mirror, a satellite disha makeup mirror, a satellite dish

5. How do we draw ray diagrams How do we draw ray diagrams
for Concave mirrors?for Concave mirrors?
It all comes back to the…It all comes back to the…
•Angle of incidenceAngle of incidence
•Incident rayIncident ray
•NormalNormal
•Reflected rayReflected ray
•Angle of reflectionAngle of reflection
SO… How do you do this on a SO… How do you do this on a
curved surface?curved surface?

6. You apply the SAME rules of You apply the SAME rules of
reflectionreflection
If you could make the mirror If you could make the mirror
INFINITELY small, you would notice INFINITELY small, you would notice
that for an instant the mirror acts that for an instant the mirror acts
like a flat plane at the point where like a flat plane at the point where
light hits itlight hits it
Therefore, you could consider that Therefore, you could consider that
the curved mirror is made up of the curved mirror is made up of
MANY small flat mirrorsMANY small flat mirrors

7. Starting with the normalStarting with the normal
If a normal (perpendicular line) is drawn If a normal (perpendicular line) is drawn
from each of the ‘flat’ parts of the from each of the ‘flat’ parts of the
curved mirror what do you notice?curved mirror what do you notice?
All the lines will meet up at the same All the lines will meet up at the same
pointpoint
This is called the CENTER OF CURVATUREThis is called the CENTER OF CURVATURE
The centre horizontal line is the
PRINCIPLE AXIS

8. The Principle AxisThe Principle Axis
It is an important feature because it It is an important feature because it
helps you locate the positions of objects helps you locate the positions of objects
that are in front of the mirrorthat are in front of the mirror
The spot where the principle axis touches The spot where the principle axis touches
the mirror is called the VERTEX or Vthe mirror is called the VERTEX or V
If an incident ray goes through the center If an incident ray goes through the center
of curvature it gets reflected back on of curvature it gets reflected back on
itself - JUST LIKE IT DOES when light hits itself - JUST LIKE IT DOES when light hits
a plane mirror through the normal a plane mirror through the normal
(remember the center of curvature is (remember the center of curvature is
where the normal all meet)where the normal all meet)

9. Rays Parallel to the Center of Rays Parallel to the Center of
CurvatureCurvature
When rays run parallel to the When rays run parallel to the principal axisprincipal axis
what do you notice?what do you notice?
They intersect at the same point on the They intersect at the same point on the
principal axisprincipal axis
This know as the This know as the FOCAL POINTFOCAL POINT or or FF
And the distance from the mirror And the distance from the mirror (V=vertex)(V=vertex) to to
the focal point is called the the focal point is called the FOCAL LENGTHFOCAL LENGTH

10. So how do we Draw the So how do we Draw the
Diagram?Diagram?
The best way to begin?The best way to begin?
Put the bottom of the object on the Put the bottom of the object on the
principle axisprinciple axis
Because the principle axis is ALSO a Because the principle axis is ALSO a
normal, this means our IMAGE will normal, this means our IMAGE will
also be on the principle axisalso be on the principle axis
The next step is to find the TOP of the The next step is to find the TOP of the
image in order to complete the image in order to complete the
diagramdiagram

11. How to draw Objects How to draw Objects
between the Focal Point and between the Focal Point and
the Mirrorthe Mirror

16. What do you notice
about the image?
RIGHT-SIDE UP and
BEHIND the mirror

17. What if the Object is between the What if the Object is between the
Focal Point and the Center of Focal Point and the Center of
Curvature?Curvature?

18. The Process is the The Process is the
SameSame

21. What do you What do you
notice about the notice about the
image?image?
UPSIDE-DOWN UPSIDE-DOWN
and in front of the and in front of the
center of center of
curvaturecurvature

22. What about when the object is in What about when the object is in
front of (or beyond) the Center of front of (or beyond) the Center of
CurvatureCurvature

26. What do you notice What do you notice
about the image?about the image?
It’s UPSIDE DOWN It’s UPSIDE DOWN
and SMALLERand SMALLER

27. You can also Predict what your You can also Predict what your
image looks like using equations!image looks like using equations!

28. Lets try a Practice ProblemLets try a Practice Problem
PG 426PG 426
A concave mirror has a focal length A concave mirror has a focal length
of 12cm. An object with a height of of 12cm. An object with a height of
2.5cm is placed 40.0cm in front of 2.5cm is placed 40.0cm in front of
the mirrorthe mirror
A) calculate the image distanceA) calculate the image distance
B) calculate the image heightB) calculate the image height

29. More PracticeMore Practice
Read pages 419-430Read pages 419-430
TB: questions 427, 1-5TB: questions 427, 1-5
WB: pg 134-136WB: pg 134-136
STSE: TB 428-429 due MondaySTSE: TB 428-429 due Monday