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Curved Mirrors

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.

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Curved Mirrors

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  1. Curved Mirrors

  2. 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?

  3. sol.sci.uop.edu

  4. 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?

  5. Drawing by Paul Hewitt

  6. 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?

  7. 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.

  8. 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 ( = thelength from the mirror to the screen). • Now do the Activity: “Focal Length” • Then do the Lab: “Curved Mirrors.”

  9. Tracing Light Raysfor Curved Mirrors

  10. The Solar Cooker S U N Drawing found at http://library.thinkquest.org/03oct/02144/glossary/concave_mirror.html

  11. 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.

  12. Mirror Where would you put a screen to make the smallest bright dot?

  13. Screen Notice: This point is not the focal point

  14. 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.

  15. 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.

  16. 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).

  17. 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).

  18. 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).

  19. 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).

  20. R C f

  21. 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.]

  22. Plane Mirror Ray of Sunlight In which way will the ray reflect?

  23. Plane Mirror Ray of Sunlight Why does it go that way?

  24. qI qR The reason: The angle of ‘incidence’ equals the angle of ‘reflection.’

  25. Plane Mirrors Ray of Sunlight Ray of Sunlight In which way do they bounce? Ray of Sunlight Ray of Sunlight Ray of Sunlight

  26. Replace the plane mirrors with a curved mirror.

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

  28. What would happen if the light originated from the focal point?

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

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

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

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

  33. The light from the pencil point bounces off the mirror following the pattern: qI = qR. P• P is not the focal point 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.

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

  35. •E 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?

  36. E P 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).

  37. 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.

  38. 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.

  39. Where is the image?What size is the image?

  40. Case One. Use the full- sized page in your booklet Object Mirror Focal Point Principal Axis

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

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

  43. Somewhere along this ray is the image, but where? 1 1

  44. In which direction will this ray bounce? Hint: this is a ‘Flashlight’ ray.

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

  46. These two principal rays help us find the location and size of the image: 1 2 2 1

  47. Real or Virtual? Object 1 2 Image 2 1

  48. ALL RAYS FROM THE TOP OF THE OBJECT (that hit the mirror) WILL PASS THROUGH THE “TOP” OF THE IMAGE Object 1 2 Image 2 1 The image is Real, Inverted, and Smaller than the object.

  49. In which direction does this 3rd ray bounce? 1 2 2 1

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