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Curved Mirrors. Take a look at a curved mirror. Where can one find a mirror of this type in real life? The image you are looking at seems to be behind the mirror. The image is (select one) larger / smaller than the object?. sol.sci.uop.edu. Handle a Flexible Mirror. - PowerPoint PPT Presentation
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Take a look at a curved mirror
• Where can one find a mirror of this type in real life?
• The image you are looking at seems to be behind the mirror.
• The image is (select one) larger / smaller than the object?
Handle a Flexible Mirror• What kitchen utensil is this like?
• Concave or Convex?– TV mirror– Inside of spoon– Outside of spoon
• Can you demonstrate both of the cases that are on the next slide?
Types of Images• We say that an image is “Virtual” if no light is actually
coming from the image location. Virtual images are never on a screen.
• We say that an image is “Real” if the light is really coming from the image location. Real images are always on a screen.
• Real or Virtual?– Image from Plane Mirror?– Image from Overhead Projector?– Image due to concave side of spoon?– Image due to convex side of spoon?
Demo: A BIG concave mirror can focus light from the Overhead
Projector onto the ceiling.
• Similar Demo: A small curved mirror can focus light from the room lights onto a piece of paper.
• Demo: A curved mirror can make an image of the window on the wall.
Focus !• A curved mirror has a focal point.
• A curved mirror has a focal length.
• To measure the focal length:– Use light from an object that is far away.
(windows, sun, light from across the room …)– Focus the light onto a screen. – Measure the focal length ( = the length from
the mirror to the screen).
• Now do the Activity: “Focal Length”
• Then do the Lab: “Curved Mirrors.”
The Solar Cooker
SUN
Drawing found athttp://library.thinkquest.org/03oct/02144/glossary/concave_mirror.html
The Solar Cooker
• Where (in the picture) do you put the food?
• What shape is the mirror?
• If it is a paraboloid, it works better than a spherical mirror, but it costs more.
The cheapest curved mirrors are made of a section of a sphere.
• These are called “_ _ _ _ _ _ _ _ _” mirrors even though they are merely part of the sphere.
The cheapest curved mirrors are made of a section of a sphere.
• These are called “spherical” mirrors even though they are merely part of the sphere.
The cheapest curved mirrors are made of a section of a sphere.
• These are called “spherical” mirrors even though they are merely part of the sphere.
• The distance from the mirror to the center of the sphere is called the _ _ _ _ _ _ (of course).
The cheapest curved mirrors are made of a section of a sphere.
• These are called “spherical” mirrors even though they are merely part of the sphere.
• The distance from the mirror to the center of the sphere is called the radius (of course).
The cheapest curved mirrors are made of a section of a sphere.
• These are called “spherical” mirrors even though they are merely part of the sphere.
• The distance from the mirror to the center of the sphere is called the radius (of course).
• The distance from the mirror to the focal point (the “focal length”) is half of the radius. f = ______ ÷ 2 (see next slide).
The cheapest curved mirrors are made of a section of a sphere.
• These are called “spherical” mirrors even though they are merely part of the sphere.
• The distance from the mirror to the center of the sphere is called the radius (of course).
• The distance from the mirror to the focal point (the “focal length”) is half of the radius. f = Radius÷2 (see next slide).
Why do concave mirrors bring sunlight to a focus?
[Note: Sunlight comes from so far away, that the rays arrive here
essentially parallel to each other.]
Ray of Sunlight
Plane Mirrors
In which way do they bounce?
Ray of Sunlight
Ray of Sunlight
Ray of Sunlight
Ray of Sunlight
The light from the pencil point bounces off the mirror following the pattern: I = R.
What would you see if you put your eye at point P, and looked at the mirror?What would you see on a screen placed at point P? The ‘image’ of the point is at P.
P•P is not thefocal point
Following the pattern: I = R, the light bounces off of the mirror, forming an image of just the eraser at point E. What would you see if you put your eye at point E?
P••E
Put a screen at points E and P (and all points in between) and you will see an image of the pencil (smaller, and inverted).
P E
Is the image real or virtual?
• We say that an image is “Virtual” if no light is actually coming from the image location.
• We say that an image is “Real” if the light is really coming from the image location.
About the image• Why do you need a screen to see this
image?
• If you cover part of the pencil how would that change the image? Explain.
• If you cover part of the mirror how would that change the image? Explain.
ALL RAYS FROM THE TOP OF THE OBJECT (that hit the mirror) WILL PASS THROUGH THE “TOP” OF THE IMAGE
2
2
1
1
The image is Real, Inverted, and Smaller than the object.
Object
Image
Sign Conventions (Page 1)
DI > 0 Image is Real and Inverted
DI < 0 ?
[Think of an example you have seen.]
Sign Conventions (Page 2)
M > 0 Image is Virtual and Upright
M < 0 ?
[Think of an example you have seen.]
Case 3
Measured w Ruler
Calculated
f -54 mm
DO 84 mm
DI -33 mm
HO 26 mm
HI 10 mm
Why is this negative?
Recall from the lab, how are Object Distance, and Image
Distance Related?
Do far objects make images near the mirror, or far from the mirror?
Image Distance vs. Object Distance[Where is the focal length on the x axis?]
-300
-200
-100
0
100
200
300
0 20 40 60
http://www.physicsclassroom.com/Class/refln/U13L3a.html
Would you like to run through the whole analysis again, but from a different source?Consider:
http://www.sasked.gov.sk.ca/docs/physics/u3b32phy.html
Would you like a source that does a detailed job of summarizing the crucial ideas? Try:
http://library.thinkquest.org/10796/ch10/mirror.htm
Would you like a resource that just deals with the big ideas? Try: