# curved mirrors

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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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• Curved Mirrors

• Take a look at a curved mirrorWhere 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 MirrorWhat kitchen utensil is this like?Concave or Convex?TV mirrorInside of spoonOutside of spoonCan you demonstrate both of the cases that are on the next slide?

• Drawing by Paul Hewitt

• Types of ImagesWe 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 LengthThen do the Lab: Curved Mirrors.

• Tracing Light Raysfor Curved Mirrors

• The Solar CookerSUNDrawing found athttp://library.thinkquest.org/03oct/02144/glossary/concave_mirror.html

• The Solar CookerWhere (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.

• Where would you put a screento make the smallest bright dot?Mirror

• ScreenNotice:This point is notthe focal point

• 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 = Radius2 (see next slide).

• CfR

• 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 SunlightPlane MirrorIn which way will the ray reflect?

• Ray of SunlightPlane MirrorWhy does it go that way?

• The reason:The angle of incidence equalsthe angle of reflection.qIqR

• Ray of SunlightPlane MirrorsIn which way do they bounce?Ray of SunlightRay of SunlightRay of SunlightRay of Sunlight

• Replace the plane mirrors witha curved mirror.

• This is how a TV Satellite Dish works.(The electromagnetic rays are collected at the receiver.)

• What would happen if the light originated from the focal point?

• Light emanates in all directions.What happens to the light that hits the mirror?

• This is how a light bulb is used as a car headlight or in a flashlight.

• Why are images created?(This is a different idea than the hot-dog cooker and the flashlight.)

• Most of the light from the pencil point does not hit the mirror.

• The light from the pencil point bounces off the mirror following the pattern: qI = qR.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.PP is not thefocal point

• Most of the light that leaves the eraser, does not hit the mirror.P

• Following the pattern: qI = qR, 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?PE

• 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 imageWhy 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.

• Where is the image?

What size is the image?

• ObjectPrincipal AxisFocal PointMirrorCase One. Use the full-sized page in your booklet

• In which direction will this ray bounce?Hint: This is a Solar Cooker ray.

• Principal Ray #1Starts parallel to the Principal Axis, and reflects through the focal point.11

• 11Somewhere along this ray is the image,but where?

• In which direction will this ray bounce?Hint: this is a Flashlight ray.

• Principal Ray #2From the focal point, it reflects parallel to the Principal Axis.22

• These two principal rays help us find the location and size of the image:2211

• Real or Virtual?2211ObjectImage

• ALL RAYS FROM THE TOP OF THE OBJECT (that hit the mirror) WILL PASS THROUGH THE TOP OF THE IMAGE2211The image is Real, Inverted, and Smaller than the object.ObjectImage

• In which direction does this 3rd ray bounce?2211

• In which direction does this 3rd ray bounce?2211

• Case Two:The object is close to the mirrorPrincipal AxisObjectFocal PointMirror

• In which way does the ray bounce?1

• Ray 1 [What is the next ray we should draw?]11This ray should lineup with the focal point

• In which way does the ray bounce?2

• Ray 222

• Lets look at all of the rays we know about, at one time.

• What does this mean?

• Real or Virtual?

• Did you see an image like this in Lab? Describe the image.

• In which direction does this 3rd ray bounce?In which direction does this 3rd ray bounce?

• In which direction does this 3rd ray bounce?In which direction does this 3rd ray bounce?

• What kind of mirror is this? [How do you know?]

• Case Three:The mirror is convex.

• In which direction does the light bounce?

• Ray 1[What is the next ray we should draw?]11

• In which direction does the ray reflect?

• Ray 222

• All the rays at once:Where is the image?1122

• Describe the image.

• http:// PhysicsClassroom.htmlWhich case is this (1, 2, or 3) ?

• An Equation that gives the location of the image:

• An equation that gives thesize of the image:

• Use the drawings we made to see if we understand how to use the equations.

• Case 1

Measured w RulerCalculatedfmmDOmmDImmmmHOmmHI - mmmm

• f

• Case 1

Measured w RulerCalculatedf56 mmDOmmDImmmmHOmmHI - mmmm

• DO

• Case 1

Measured w RulerCalculatedf56 mmDO183 mmDImmmmHOmmHI - mmmm

• DI

• Case 1

Measured w RulerCalculatedf56 mmDO183 mmDI76 mm mmHOmmHI - mm - mm

• HO

• Case 1

Measured w RulerCalculatedf56 mmDO183 mmDI76 mm mmHO25 mmHI - mm - mm

• HI

• Case 1

Measured w RulerCalculatedf56 mmDO183 mmDI76 mm ? mmHO25 mmHI - 10 mm - mm

• What numbers do you put in?

• Put in the numbers

• What number do you get?

• Sign Conventions (Page 1)DI > 0 Image is Real and Inverted DI < 0 ?[Think of an example you have seen.]

• Case 1

Measured w RulerCalculatedf56 mmDO183 mmDI76 mm81 mmHO25 mmHI - 10 mm - ? mm

• What numbers do you put in?

• What number do you get?

• Case 1

Measured w RulerCalculatedf56 mmDO183 mmDI76 mm81 mmHO25 mmHI - 10 mm - 11 mm

• What is the magnification?M = HI HO

• M = HI HOM = (-11)(25)M = -0.44

• Sign Conventions (Page 2)M > 0 Image is Virtual and UprightM < 0 ?[Think of an example you have seen.]