April 2011 General Science

Bending Light Thursday April 12 th, 2012 Warm-up: 1. What is the angle of reflection equal to? Objective: Students will be able to analyze changes in the speed of light passing between two media in order to describe the direction of light refraction. Homework: Wave Interactions HW #3

Hmmm?

Bending LightINBOXFrom Date: Today Hey, I just called the teen club to find out a little more about the applications for the lighting specialist and they said that they were hoping to do a lot with refracted light. I know that refracted light is somehow bent as it goes through something, but how you figure out which way it will bend, I have no clue. If we want to have a shot at this job, we better figure it out! INBOX From

Classwork 1. Predict what do you think will happen … when the laser beam travels through the gelatin. 2. Observe the demonstration as conducted by your teacher. 3. Using a complete sentence, summarize the changes you observed during the investigation.

4. Refer to the photo on the other paste-in. Follow the directions. Labeling Figure 1: Gelatin Refraction Photo Surface Line Normal Incident Ray Refracted Ray 1.__________ _____ - refers to the surface or outside of the medium 2.__________ - refers to the normal path in which light travels 3.__________ _____ - this is the beginning of the laser beam before it enters the medium 4.__________ _____ - refers to the laser beam after it the medium

Classwork The angle between the indent ray and the normal line is called the angle of incidence while the angle between the refracted ray and the normal line is called the angle of refraction. Surface Line Normal Incident Ray Refracted Ray

Classwork 5. Compare the angle formed by the incident ray and the normal line with the angle formed by the refracted ray and the normal line. (write this in your notebook) 6. Share what you had for number 5 with the person you are sitting next to. Fill in the following statement about this comparison on your white board. When light passes from air into the gelatin, the angle of incidence is _______ _______ the angle of refraction.

greater than

Classwork: Reading Strategies Before Reading: Based on the titles of Figure 2 and Figure 3, what will we be learning from each reading? 7. Why did the light bend? During Reading: Underline information in each paragraph that tells you why light slows down and speeds up. After Reading: What did you underline in each reading?

Why Light Bends You just observed refraction, or the bending of light. Light can travel through many materials, although it does so at different speeds. When light passes from a medium such as air into a second medium, such as water, the speed of light changes. This change in speed causes the light to bend. In order to figure out whether light is speeding up or slowing down, you need to compare the direction the light ray bends. If a light ray bends towards the normal line, this bending towards the normal means that the speed of light has decreased when it entered the new media. This is illustrated in Figure 2, Light Slowing Down. FIGURE 2 LIGHT SLOWING DOWN Incident Ray Faster Light Speed Slower Light Speed Refracted ray bends towards normal Normal Line

Why Light Bends You just observed refraction, or the bending of light. Light can travel through many materials, although it does so at different speeds. When light passes from a medium such as air into a second medium, such as water, the speed of light changes. This change in speed causes the light to bend. In order to figure out whether light is speeding up or slowing down, you need to compare the direction the light ray bends. If a light ray bends towards the normal line, this bending towards the normal means that the speed of light has decreased when it entered the new media. This is illustrated in Figure 2, Light Slowing Down. FIGURE 2 LIGHT SLOWING DOWN Incident Ray Faster Light Speed Slower Light Speed Refracted ray bends towards normal Normal Line

Why Light Bends You just observed refraction, or the bending of light. Light can travel through many materials, although it does so at different speeds. When light passes from a medium such as air into a second medium, such as water, the speed of light changes. This change in speed causes the light to bend. In order to figure out whether light is speeding up or slowing down, you need to compare the direction the light ray bends. If a light ray bends towards the normal line, this bending towards the normal means that the speed of light has decreased when it entered the new media. This is illustrated in Figure 2, Light Slowing Down. FIGURE 2 LIGHT SLOWING DOWN Incident Ray Faster Light Speed Slower Light Speed Refracted ray bends towards normal Normal Line

If you see the light bending away from the normal line when entering a new media, the bending away means that the light has increased in speed. This is shown in Figure 3, Light Speeding Up. Incident Ray Faster Light Speed Slower Light Speed Refracted ray bends away from normal. Normal Line FIGURE 3 LIGHT SPEEDING UP

If you see the light bending away from the normal line when entering a new media, the bending away means that the light has increased in speed. This is shown in Figure 3, Light Speeding Up. Incident Ray Faster Light Speed Slower Light Speed Refracted ray bends away from normal. Normal Line FIGURE 3 LIGHT SPEEDING UP

Concept Check 10. Was the light moving faster or slower through the gelatin?

Practice: Slower or Faster?

Surface Line Normal ANSWER: Slower As the light enters the water (red line), the light refracts (blue line). The light is moving slower because the angle of refraction is smaller than the angle of incidence.

Practice: Slower or Faster?

ANSWER: Faster As the light enters the air, the light refracts. The light is moving faster because the angle of refraction is greater than the angle of incidence.

Exit Ticket You have to capture the fish from the classroom aquarium. You see the image of the fish at location B as you stare through the waters surface. What location would you need to aim you net to catch the fish? Location A, Location B, or Location C? Support your answer using knowledge of refraction of light. (HINT- The speed of light decreases as the light wave leaves the air and enters water.)

Exit Ticket You have to capture the fish from the classroom aquarium. You see the image of the fish at location B as you stare through the waters surface. What location would you need to aim you net to catch the fish? Location A, Location B, or Location C? Support your answer using knowledge of refraction of light. (HINT- The speed of light decreases as the light wave leaves the air and enters water.)