# Optics Learning Goals Fa13

Unit 2 for Physics 3 covered wave and geometric optics…

**Content Learning Goals**

1. Use Snell’s Law to qualitatively sketch light rays as they pass between different mediums for flat and curved boundaries between the mediums. Student can also use Snell’s Law and the definition of index of refraction to mathematically relate angles, indices, and speeds.

2. Explain the meaning of total internal reflection and when it is and is not possible. Student can sketch ray diagrams for θ < θ_{c}, θ = θ_{c}, and θ > θ_{c} and can solve for the value of θ_{c}.

3. Explain the difference between specular and diffuse reflection, when each occurs, and how both types of reflection obey the law of reflection (θ_{in} = θ_{out}).

4. Use geometry and the law of reflection to draw ray diagrams showing light reflecting off multiple plane mirrors.

**** Several students had more difficulty using geometry (constructing triangles and straight lines with angles summing to 180 degrees to find unknown angles) than I anticipated.*

5. Use principal rays and the lens equation to locate the image formed by a concave or convex thin lens. Student can compare the location, size, and orientation of the object and the image.

6. Use principal rays to locate the image formed by a concave or convex mirror. Student can compare the location, size, and orientation of the object and the image.

**** In the interest of time, I decided to only cover mirrors qualitatively. We used the law of reflection to sketch approximate light rays and locate the approximate image but we did not end up covering principal rays or equations for mirrors.*

7. Use principal rays and the lens equation to locate the final image formed by a pair of lenses or a combination of a lens and a mirror. Student can compare the location, size, and orientation of the original object and the final image.

8. Explain the difference between real and virtual images and classify the images in goals 5 – 7 as real or virtual.

9. Explain Huygen’s principle and use it to explain why ray optics works well when the wavelength is small compared to the objects or slits the light interacts with but does not work well when the wavelength is similar to or smaller that the size of the objects or slits.

10. Sketch a double slit diagram and use the diagram to derive an equation for the location of the bright spots on the screen. Student can use this equation to solve double slit or diffraction grating problems. Student can also apply the same reasoning to a “double speaker” scenario involving sound.

11. Explain how the results of a double slit experiment suggest that light behaves as a wave rather than a particle.

12. Explain what it means for light to be coherent and why light must be coherent in order to produce an observable interference pattern.

13. Explain what causes thin film interference and relate film thickness and wavelength for cases of constructive and destructive interference.

14. Explain why white light produces a rainbow when a) it passes through a prism, b) it passes through a diffraction grating, and c) it reflects off a thin film.

15. Explain what polarization means and calculate the intensity of polarized or unpolarized light after it passes through a polarizer.

**** The learning goal about antennas for detecting EM waves got moved from Unit 1 to this Unit to go along with polarization.*

**General Skills Related to this Unit**

1. Thinking in terms of diagrams. In this unit we will make extensive use of ray diagrams as well as wave diagrams to help us solve problems. As with any diagram we draw in science and engineering, these diagrams help us to present and organize information and physical principles in a way that allows us to apply ideas one at a time and then quickly see their cumulative effect.

2. Applying a single principle across multiple contexts. Our solutions for multi-slit, multi-source, and thin-film interference problems will all hinge on our ability to understand and apply the concept of a path length difference. Our success will be greatly aided by our decision to represent all three scenarios in a format (a wave diagram) that highlights the common aspect of path length difference.

**Experiential Value of this Unit**

1. The section on ray optics will prepare you to view many of the optical phenomena in daily life in terms of light rays. When you see a faint reflection in a bus window or on a shiny surface you may find yourself instinctively tracing light rays in your mind to locate the object whose reflection you are viewing. You will also be increasingly aware of distortions and tricks played by refraction. You will see everyday objects in terms of lenses and will always smile when you see a “wet road mirage” on a hot day.

2. This unit will further emphasize the amazing phenomenon of interference and superposition. We introduced this topic last unit but when you really see and think about interference with light you start to glimpse the truly strange and wonderful behavior of nature.