Reflection & Refraction

1. Reflection & Refraction Physics 1161: Lecture 17 • Textbook sections 26-3 – 26-5, 26-8

2. Preflight 17.1 Which ray is NOT correct? p.a. 36% 1) R f 2) 45% 3) 18%

3. Preflight 17.1 Which ray is NOT correct? Ray through center should reflect back on self. p.a. 1) R f 2) 3)

4. Preflight 17.3 The image produced by a concave mirror of a real object is: • Always Real • Always Virtual • Sometimes Real, Sometimes Virtual 30% 30% 39%

5. Where in front of a concave mirror should you place an object so that the image is virtual? • Close to mirror • Far from mirror • Either close or far • Not Possible

6. Where in front of a concave mirror should you place an object so that the image is virtual? • Close to mirror • Far from mirror • Either close or far • Not Possible

7. Preflight 17.2 Compared to the candle, the image will be: • Larger • Smaller • Same Size Example Solving Equations A candle is placed 6 cm in front of a concave mirror with focal length f=2 cm. Determine the image location. p.a. R f 29% 59% 12%

8. Preflight 17.2 Compared to the candle, the image will be: • Larger • Smaller • Same Size Example Solving Equations A candle is placed 6 cm in front of a concave mirror with focal length f=2 cm. Determine the image location. di = + 3 cm (in front of mirror) Real Image! p.a. R f

9. C C C F F F Object Image Image Object Object Image 3 Cases for Concave Mirrors Upright Enlarged Virtual Inside F Inverted Enlarged Real Between C&F Inverted Reduced Real Past C Physics 1161: Lecture 17, Slide 9

10. Example Solving Equations A candle is placed 6 cm in front of a convex mirror with focal length f=-3 cm. Determine the image location. Determine the magnification of the candle. If the candle is 9 cm tall, how tall does the image candle appear to be?

11. Virtual Image! Image is Upright! Example Solving Equations A candle is placed 6 cm in front of a convex mirror with focal length f=-3 cm. Determine the image location. Determine the magnification of the candle. If the candle is 9 cm tall, how tall does the image candle appear to be? di = - 2 cm (behind mirror) m = + 1/3 hi = + 3 cm

12. Preflight 17.4 The image produced by a convex mirror of a real object is ? • Always real • Always virtual • Sometimes real and sometimes virtual 24% 61% 15%

13. Mirror Summary • Angle of incidence = Angle of Reflection • Principal Rays • Parallel to P.A.: Reflects through focus • Through focus: Reflects parallel to P.A. • Through center: Reflects back on self • |f| = R/2

14. Indices of Refraction Physics 1161: Lecture 17, Slide 14

15. Snell’s Law When light travels from one medium to another the speed changes v=c/n, but the frequency is constant. So the light bends: n1 sin(q1)= n2 sin(q2) Preflight 17.6 n1 q1 1) n1 > n2 2) n1 = n2 3) n1 < n2 21 % q2 n2 21 % Compare n1 to n2. 58 %

16. Snell’s Law When light travels from one medium the speed changes. If the angle of incidence is greater than 0, the light bends. During this process, the frequency remains constant. n1 sin(q1)= n2 sin(q2) Preflight 17.6 n1 q1 1) n1 > n2 2) n1 = n2 3) n1 < n2 q1 < q2 q2 n2 sinq1< sinq2 n1> n2 Compare n1 to n2.

17. Example Snell’s Law Practice 1 r Usually, there is both reflection and refraction! A ray of light traveling through the air (n=1) is incident on water (n=1.33). Part of the beam is reflected at an angle qr = 60. The other part of the beam is refracted. What is q2? n1 n2 normal

18. Example Snell’s Law Practice 1 r Usually, there is both reflection and refraction! A ray of light traveling through the air (n=1) is incident on water (n=1.33). Part of the beam is reflected at an angle qr = 60. The other part of the beam is refracted. What is q2? q1 =qr =60 sin(60) = 1.33 sin(q2) n1 q2 = 40.6 degrees n2 normal

19. F P.A. Object F Which way should you move object so image is real and diminished? • Closer to the lens • Farther from the lens • A converging lens can’t create a real, diminished image.

20. F P.A. Object F Which way should you move object so image is real and diminished? • Closer to the lens • Farther from the lens • A converging lens can’t create a real, diminished image.

21. Image Object Image Image Object Object 3 Cases for Converging Lenses Past 2F Inverted Reduced Real This could be used in a camera. Big object on small film Between F & 2F Inverted Enlarged Real This could be used as a projector. Small slide on big screen Inside F Upright Enlarged Virtual This is a magnifying glass

22. Diverging Lens Principal Rays Example F P.A. Object F 1) Rays parallel to principal axis pass through focal point. 2) Rays through center of lens are not refracted. 3) Rays toward F emerge parallel to principal axis. Image is (always true): Real or Imaginary Upright or Inverted Reduced or Enlarged

23. Diverging Lens Principal Rays Image Example F P.A. Object F 1) Rays parallel to principal axis pass through focal point. 2) Rays through center of lens are not refracted. 3) Rays toward F emerge parallel to principal axis. Image is virtual, upright and reduced.

24. F P.A. Object F Which way should you move the object to cause the image to be real? • Closer to the lens • Farther from the lens • Diverging lenses can’t form real images

25. F P.A. Object F Which way should you move the object to cause the image to be real? • Closer to the lens • Farther from the lens • Diverging lenses can’t form real images