Ray Model A useful model under certain circumstances to explain image formation. Ray Model: Light travels in straight-line paths, called rays, in ALL directions from the source.

Experiment with plane mirror

Law of Reflection   A ray reflects from a plane mirror at the same angle, with respect to the normal, that it is incident on the mirror.

The image point is the point from which light rays spread out, or diverge, as they approach your eye.

... towards your eye A B C. D Light from a candle flame reaches a reflecting surface (not shown). The diagram shows two of the rays reflected from this surface to your eye, which sees a single image of the flame. Which letter indicates the location of this image?

Real and Virtual Images virtual image - light does not pass through the image point real image - light passes through the image point

How we “see” laser pointer wall diffuse reflection occurs when the surface is irregular Thus, each part of an illuminated object acts as a point source.

Image of an Extended Object

Example What portion of the person’s body will he/she see in the mirror?

Poll If the mirror is brought closer, the person will see 1.more of his body 2.less of his body 3.the same amount of his body

A. c loser to the mirror surface B. further from the mirror surface C. further to the left D. further to the right E. in the same place as before F. [more than one answer is correct] mirror Image If the observing eye is moved to the new position shown, the image it sees will appear ________ Object old new

 1 2      Plane mirror 43 5 O For which (one or more) of the point objects 1, 2, 3, 4, and 5 can an observer at O see an image in the plane mirror? A. 2 and 3 B. 3, 4, and 5 C. 2, 3, and 5 D. 2, 3, 4, and 5 E. 1, 2, 3, and 4 F. all

More than one mirror The image in the first mirror becomes the object for the second mirror.

1 m Mirror AMirror B You are standing midway between two parallel plane mirrors A and B. The nearest image that you see in A appears 1 m behind the surface of A. Then the next nearest image that you see in A will appear _____ behind the surface. A. 2 m B. 3 m C. 4 m D. 5 m

Spherical Mirror

Concave Mirror

Focal point Rays parallel to the axis of the mirror pass through the focal point of the mirror.

Object distance > f

Object distance < f

Sketching ray diagrams 1.Select a single source point. 2.Sketch a ray parallel to the axis of the mirror that reflects through the focal point. 3.Sketch a ray that reflects off the center of the mirror at the mirror’s axis at an angle equal to the angle of incidence. 4.Sketch a ray that is incident normal to the mirror and reflects back through itself. 5.Sketch a ray that passes through the focal point and reflects parallel to the axis of the mirror. 6.At the intersection of these rays is the image point.

Relate object distance, image distance, and focal length sign convention for mirrors

Example An object is 10 cm from a concave mirror of focal length 20 cm. (a) What is the image distance? (b) What is the magnification? (c) Is the image real or virtual? (d) Is it inverted or upright?

. C V A ketchup bottle is positioned in front of a concave mirror. Three of the incident rays are shown. a. _________ get(s) reflected through point C. A. Ray 1 B. Ray 2 C. Ray 3 D. All three rays E. None of the rays

. C V A ketchup bottle is positioned in front of a concave mirror. Three of the incident rays are shown. b. _________ get(s) reflected horizontally to the left. A. Ray 1 B. Ray 2 C. Ray 3 D. All three rays E. None of the rays

. C V A ketchup bottle is positioned in front of a concave mirror. Three of the incident rays are shown. c. _________ make(s) the same angle with the normal as its reflected ray does. A. Ray 1 B. Ray 2 C. Ray 3 D. All three rays E. None of the rays

. C V A ketchup bottle is positioned in front of a concave mirror. Three of the incident rays are shown. d. _________ make(s) the same angle with the horizontal as its reflected ray does. A. Only ray 1 B. Only ray 2 C. Only ray 3 D. More than one of the rays E. None of the rays

. C V A concave mirror forms an image of an object as shown. object image Show in Slide Show view to have question appear in stages. front view of card edge view of card ? Suppose the top half of the mirror is blocked by an opaque card. A. no image B. an image of the entire object C. an image of just the top half of the object D. an image of just the bottom half of the object With the card in place, we see__________.

 C V The concave mirror has a radius of curvature R. At which of the numbered points could you place an object perpendicular to the central axis (like this: ) and see a. a reduced real image? R  R/  3   A. 1 B. 2 C. 3 D. 4 E. none of these

 C V The concave mirror has a radius of curvature R. At which of the numbered points could you place an object perpendicular to the central axis (like this: ) and see b. an enlarged virtual image? R  R/  3   A. 1 B. 2 C. 3 D. 4 E. none of these

 C V The concave mirror has a radius of curvature R. At which of the numbered points could you place an object perpendicular to the central axis (like this: ) and see c. a reduced virtual image? R  R/  3   A. 1 B. 2 C. 3 D. 4 E. none of these

 C V The concave mirror has a radius of curvature R. At which of the numbered points could you place an object perpendicular to the central axis (like this: ) and see d. an enlarged real image? R  R/  3   A. 1 B. 2 C. 3 D. 4 E. none of these

 C V The concave mirror has a radius of curvature R. At which of the numbered points could you place an object perpendicular to the central axis (like this: ) and see e. no image? R  R/  3   A. 1 B. 2 C. 3 D. 4 E. none of these