1. Physics for Scientists and Engineers II, Summer Semester 2009 1 Lecture 26: July 29 th 2009 Physics for Scientists and Engineers II

2. Physics for Scientists and Engineers II, Summer Semester 2009 2 Ray Diagrams for Thin Lenses Incoming RayOutgoing Ray Parallel to principal axisAs if coming from focal point in front of the lens (F1) Towards focal point behind the lens (F2) Parallel to principal axis Through center of lensGoes straight through

3. Physics for Scientists and Engineers II, Summer Semester 2009 3 Combination of Thin Lenses Similar to the procedure we used when calculating the effect of two refracting surfaces: Step 1: Ignore lens 2 and calculate the image position due to lens 1. Step 2: Determine whether image position from Step 1 is in front or behind lens 2.  In front of lens 2: Object position for lens 2 positive (real object)  Behind lens 2: Object position for lens 2 is negative (virtual object) ….and determine the distance to lens 2, of course. Step 3: Determine the image position (of the object determined in step 2) due to lens 2. Overall magnification :

4. Physics for Scientists and Engineers II, Summer Semester 2009 4 Example of Combination of Thin Lenses

5. Physics for Scientists and Engineers II, Summer Semester 2009 5 Example – Step 1 (ignore lens 2)

6. Physics for Scientists and Engineers II, Summer Semester 2009 6 Example – Step 2 (ignore lens 2)

7. Physics for Scientists and Engineers II, Summer Semester 2009 7 Example – Step 3 (ignore lens 1)

8. Physics for Scientists and Engineers II, Summer Semester 2009 8 Example of Combination of Thin Lenses

9. Physics for Scientists and Engineers II, Summer Semester 2009 9 The Simple Magnifier – Angle Subtended Eye Objects appear larger if the angle  subtended at the eye is larger. Get closer to the object and  becomes larger  object appears larger. Eye Problem: At some point the human eye can no longer focus on the object. Typically, the closest distance is 25cm, the “near point of the eye” (varies individually, especially with age).

10. Physics for Scientists and Engineers II, Summer Semester 2009 10 The Simple Magnifier Eye Adding a lens and putting eye close to the lens such that the image appears at 25cm (able to focus on the image).

11. Physics for Scientists and Engineers II, Summer Semester 2009 11 The Simple Magnifier Angular Magnification:

12. Physics for Scientists and Engineers II, Summer Semester 2009 12 The Compound Microscope – Two converging lenses

13. Physics for Scientists and Engineers II, Summer Semester 2009 13 The Compound Microscope – Magnification Magnification Using Compound Microscope:

14. Physics for Scientists and Engineers II, Summer Semester 2009 14 The Refracting Telescope

15. Physics for Scientists and Engineers II, Summer Semester 2009 15 Chapter 37: Condition for Interference of Light Waves Interference = Superposition (adding) of waves S1 S2 S1S2 Example of Constructive Interference

16. Physics for Scientists and Engineers II, Summer Semester 2009 16 Condition for Interference of Light Waves S1 S2 S1S2 Example of Destructive Interference Conditions for Interference: 1)Light from two sources must be “coherent”. That means, the relative phase between S1 and S2 must remain constant. 2)The light should be monochromatic (single wavelength).

17. Physics for Scientists and Engineers II, Summer Semester 2009 17 Young’s Double-Slit Experiment Barrier with two small openings. Monochromatic light. Diffraction of light occurs.

18. Physics for Scientists and Engineers II, Summer Semester 2009 18 Young’s Double-Slit Experiment Screen Maximum Minimum Constructive and destructive interference depending on direction.

19. Physics for Scientists and Engineers II, Summer Semester 2009 19 Center: Bright Spot Constructive interference (bright fringe on screen) Screen

20. Physics for Scientists and Engineers II, Summer Semester 2009 20 First Minimum (Destructive Interference) Destructive interference (Dark fringe on screen) Screen

21. Physics for Scientists and Engineers II, Summer Semester 2009 21 The next Maximum Constructive interference (Bright fringe on screen) Screen

22. Physics for Scientists and Engineers II, Summer Semester 2009 22 Light Waves in Interference O d S2S2 S1S1 y P Q