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Reflection from Curved Mirrors

Reflection from Curved Mirrors. Curved mirrors. The centre of the mirror is called the pole. A line at right angles to this is called the principal axis . The focal length of a mirror is half the radius of curvature.

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Reflection from Curved Mirrors

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  1. Reflection from Curved Mirrors

  2. Curved mirrors • The centre of the mirror is called the pole. • A line at right angles to this is called the principal axis. • The focal length of a mirror is half the radius of curvature. • The radius of curvature is the radius of the ball that the mirror would have been cut from.

  3. r pa P F C f Curved Mirrors f = r/2 • C = centre of curvature • r = radius of curvature • F = Focal point or focus f = focal length • pa = principal axis P = pole

  4. Concave Mirrors • Concave (or converging) mirrors focus light at the focal point.

  5. Convex Mirrors • Convex mirrors have a focal point behind the mirror. • Convex (or diverging) mirrors spread the light rays apart so that they appear to have come from the focal point

  6. Ray Diagrams • Used to find the size, nature and position of images. • The nature of an image formed by a mirror or lens can be described according to 3 characteristics: Is it • a) upright or inverted • b) magnified, diminished or the same size • c) Real or virtual

  7. Concave Mirrors • Look at your reflection in a concave mirror. The image is virtual and …………… • Move the mirror away from you. Why do you think the image has disappeared? • What happens to the image as the mirror is moved further away from the object (demo) • Think of a use for a concave mirror.

  8. Ray Diagrams • Rule One: An incident ray parallel to the pa is reflected back through the focal point. Remember that pa = principal axis

  9. Ray Diagrams • Rule Two: An incident ray that passes through the focal point on the way to the mirror is reflected back parallel to the pa.

  10. Drawing diagrams to solve problems • An object of height 5cm is placed 10 cm away from a concave mirror of focal length 6cm. Draw a ray diagram to show the location of the image. Describe the image and calculate its magnification using the formula: Magnification = height of image height of object

  11. What about drawing virtual images Page 64 in your text book. Look at example G The image is virtual because the rays of light do not meet. They seem to be coming from a point which is behind the mirror (just like a plane mirror) but because they are diverging, they give the illusion that the object is larger.

  12. Formula for Spherical Mirrors • Descartes’ Formula: • Or: • m=magnification factor • h=height of image or object • d=distance from mirror to image or object • Distances behind the mirror are negative

  13. An object of height 12cm is placed in front of a concave mirror of focal length 10cm. Complete the table

  14. Complete activity 5B (pg 67) • Complete questions 1-4

  15. Summarise images produced by concave mirrors

  16. Convex Mirrors • Images are virtual (the rays do not meet after reflection), diminished and upright.

  17. Ray Diagrams • The same 2 rules for drawing light rays can be applied to convex mirrors with a few small changes F • All convex mirror images are virtual, diminished • and upright.

  18. Name a use for convex mirrors • Car mirrors • Mirrors positions on sharp corners

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