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# Concave mirrors

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• Pg 420
• Pg 420
• Pg 420
• ### Concave mirrors

1. 1. Concave Mirrors The laws remain the same
2. 2. The Sky Mirror in Monte Carlo
3. 3. The Sky Mirror What do you notice about the mirror image you see?
4. 4. Properties of Concave Mirrors <ul><li>Concave mirrors are shaped curved like a letter C or the inside of a sphere </li></ul><ul><li>You can identify them from other mirrors because light goes into them like entering a CAVE </li></ul><ul><li>Examples: the side of spoon you put food on, a makeup mirror, a satellite dish </li></ul>
5. 5. How do we draw ray diagrams for Concave mirrors? <ul><li>It all comes back to the… </li></ul><ul><ul><li>Angle of incidence </li></ul></ul><ul><ul><li>Incident ray </li></ul></ul><ul><ul><li>Normal </li></ul></ul><ul><ul><li>Reflected ray </li></ul></ul><ul><ul><li>Angle of reflection </li></ul></ul><ul><li>SO… How do you do this on a curved surface? </li></ul>
6. 6. You apply the SAME rules of reflection <ul><li>If you could make the mirror INFINITELY small, you would notice that for an instant the mirror acts like a flat plane at the point where light hits it </li></ul><ul><li>Therefore, you could consider that the curved mirror is made up of MANY small flat mirrors </li></ul>
7. 7. Starting with the normal <ul><li>If a normal (perpendicular line) is drawn from each of the ‘flat’ parts of the curved mirror what do you notice? </li></ul><ul><li>All the lines will meet up at the same point </li></ul><ul><li>This is called the CENTER OF CURVATURE </li></ul>The centre horizontal line is the PRINCIPLE AXIS
8. 8. The Principle Axis <ul><li>It is an important feature because it helps you locate the positions of objects that are in front of the mirror </li></ul><ul><li>The spot where the principle axis touches the mirror is called the VERTEX or V </li></ul><ul><li>If an incident ray goes through the center of curvature it gets reflected back on itself - JUST LIKE IT DOES when light hits a plane mirror through the normal (remember the center of curvature is where the normal all meet) </li></ul>
9. 9. Rays Parallel to the Center of Curvature <ul><li>When rays run parallel to the principal axis what do you notice? </li></ul><ul><li>They intersect at the same point on the principal axis </li></ul><ul><li>This know as the FOCAL POINT or F </li></ul><ul><li>And the distance from the mirror (V=vertex) to the focal point is called the FOCAL LENGTH </li></ul>
10. 10. So how do we Draw the Diagram? <ul><li>The best way to begin? </li></ul><ul><li>Put the bottom of the object on the principle axis </li></ul><ul><li>Because the principle axis is ALSO a normal, this means our IMAGE will also be on the principle axis </li></ul><ul><li>The next step is to find the TOP of the image in order to complete the diagram </li></ul>
11. 11. How to draw Objects between the Focal Point and the Mirror
12. 16. What do you notice about the image? RIGHT-SIDE UP and BEHIND the mirror
13. 17. What if the Object is between the Focal Point and the Center of Curvature?
14. 18. The Process is the Same
15. 21. What do you notice about the image? UPSIDE-DOWN and in front of the center of curvature
16. 22. What about when the object is in front of (or beyond) the Center of Curvature
17. 26. What do you notice about the image? It’s UPSIDE DOWN and SMALLER
18. 27. You can also Predict what your image looks like using equations!
19. 28. Lets try a Practice Problem PG 426 <ul><li>A concave mirror has a focal length of 12cm. An object with a height of 2.5cm is placed 40.0cm in front of the mirror </li></ul><ul><li>A) calculate the image distance </li></ul><ul><li>B) calculate the image height </li></ul>
20. 29. More Practice <ul><li>Read pages 419-430 </li></ul><ul><li>TB: questions 427, 1-5 </li></ul><ul><li>WB: pg 134-136 </li></ul><ul><li>STSE: TB 428-429 due Monday </li></ul>