1. Reflection & Refraction
Formative Assessment Probes

2. This duck appears to be broken. Why is this happening?
Duck: Courtesy of Allison Hope Nichols via Flickr Spoon: Courtesy of B Rosen via Flickr

3. Why does the image of the man on the back of this spoon appear squished?

4. Teacher Notes
If refraction occurs, the light rays travel through a different medium and bend. When the light rays come back to your eye, they come back at a different angle. This can make the object appear distorted.
Let's think about the image of the duck from the first section. The top of the duck is above the water. The light rays travel through the air, reflect off the duck, and bounce back to our eyes. Our eyes interpret this as a duck sitting on the water. Half of the duck is under the water. The light rays travel through the air, the glass of the tank that is holding the water, and the water.
The light rays in this case are traveling through at least three types of media. This bending of the light rays creates the illusion that the duck is broken in half.
For teacher information

5. Teacher Notes
If reflection occurs on a flat surface, the light rays reflect back at the same angle and the object appears normal.
If reflection occurs on a curved surface, the light rays still reflect, but they reflect back at a different angle. This type of reflection gives you an image that can be distorted or appear upside down.
Students often mistake this type of reflection for refraction because the image appears distorted.
For teacher information

6. Question: Why is reflection on a curved surface not the same as refraction?
Pose question to students

7. Why is reflection on a curved surface not the same as refraction?
The answer is that any time light rays travel through only one medium, in this case air, it is reflection.
Light rays travel from the light source, through the air, hit the opaque spoon, and reflect back to our eyes to produce the image we see.
Remember, when refraction happens, the light rays must travel through one medium (air) into another medium where the rays bend.
For teacher info

8. Teacher Background - Applications
Uses of concave mirrors
Concave mirrors are commonly used in torches, search-lights and vehicles headlights to get powerful parallel beams of light.
They are often used as shaving mirrors to see a larger image of the face.
The dentists use concave mirrors to see large images of the teeth of patients.
Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.
Teachers – provide real world examples to students throughout the unit of student

9. Teacher Background - Applications
Uses of convex mirrors
Convex mirrors are commonly used as rear-view (wing) mirrors in vehicles.
These mirrors are fitted on the sides of the vehicle, enabling the driver to see traffic behind him/her to facilitate safe driving.
Convex mirrors are preferred because they always give an erect, though diminished, image.
Also, they have a wider field of view as they are curved outwards.
convex mirrors enable the driver to view much larger area than would be possible with a plane mirror.
Teachers – provide real world examples to students throughout the unit of student

10. Examples

11. Checkpoint
Seeing your face distorted in a funhouse mirror is an example of ________.
Seeing a prism transform white light into a rainbow is an example of ________.
Quick check of student understanding.
#1 is reflection
#2 is refraction

12. Checkpoint
________ is when light rays travel through one medium and bounce off a second medium.
Diving for rings on the bottom of the pool and discovering they are not exactly in the place they appear to be is an example of ________.
Quick check of student understanding
#3 is reflection
#4 is refraction