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Try to think back to when you used a spoon to mix drink crystals with water. The part of the spoon you see through the water may appear to be slightly out of position.
When a light travels through the boundary or edge of a transparent substance, such as water or a glass, changes to the light occur at the boundary. What happens to the light that passes through the boundary? Could those changes explain why the spoon appears to be displaced? That's the subject of this lesson. You will investigate the path light follows as it is transmitted from one substance into another.
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When light passes from one transparent or translucent substance - a medium for light - into another, it is likely refracted. Refraction is a fundamental or basic property of light.
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Remember that you see an object - such as your finger - because light from a source is reflected from the object to your eyes. Figure 3.26 on page 200 in the textbook illustrates the phenomenon. You can imagine that if you were spearing a fish for lunch, you would have to aim lower than where the fish appeared to be or go hungry!
Read the introduction to refraction on page 200 of the textbook for an explanation of why the refraction of light occurs.
1. The speed of light is affected by the substance it travels through.
a. What is the speed of light in air, glass, and diamonds?
b. The densities of these materials are 0.0013 g/mL, 2.6 g/cm3, and 3.5 g/cm3, respectively (1 mL = 1 cm3). Based on the data provided, write a prediction about the relationship between the density of a material and the speed at which light travels through it.
2. Use the concept of refraction to explain why it is likely that a young bear's first salmon-fishing expedition will be unsuccessful.
Find Out Activity
The Re-appearing Coin
Refer to the activity on page 200 of the textbook.Follow the steps of "Procedure" with a partner, if possible. Relate your observations to the concept illustrated in Figure 3.26.
3. Answer the question in "What Did You Find Out?"
I n v e s t i g a t i o n 3C
When Light Refracts
Refer to the "Inquiry Investigation" on page 201 of the textbook.Carefully read the entire investigation. Then do the steps of "Procedure."
4. Answer questions 1 to 4 of "Analyze" and "Conclude and Apply."
Going Around the Bend with Light
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Generally, when light travels from one medium to another that is more dense, the light will bend toward the normal. Going into a less-dense medium, light will bend away from the normal.
PhotoDisc Collection/Getty Images
PhotoDisc Collection/Getty Images
A rectangular prism of an unknown substance is submerged in water. A ray of light enters the prism from the water at point A and is refracted as shown in the diagram.
b. Predict the path the refracted ray will follow at B - path 1 or 2?
I n v e s t i g a t i o n 3D
Follow That Refracted Ray!
Refer to the "Inquiry Investigation" on pages 202 and 203 in the textbook. Read through the entire investigation.Look at the photo on page 202 to see a ray box. The electrical device in the picture is a ray box, which makes a beam of light. If you don't have a ray box you won't have to actually do the investigation. Sample results will be included so you can still think your way through the investigation.
Follow these general tips if you have a ray box:
6. Identify and list your manipulated variable, responding variable, and at least one controlled variable for this science question:
How does the density of a liquid affect the amount of bending toward the normal?
Suppose you have a way of sending a narrow beam of light through a transparent container. The container is like that in the diagram on page 202. The container is transparent and shaped like a shallow aquarium. You can fill it with various liquids.
7. Write down two questions you could investigate with such an apparatus and materials.
8. Write your hypothesis for an investigation about the refraction of light.
9. Do steps 1 and 2 of "Procedure." Briefly describe your procedure. If you do not have a group to work with, talk about your plans with a friend or family member.
Note: When preparing actual-size diagrams to record your observations, start one diagram in the following way:
Step 1: Draw an oblique straight line on the sheet of paper. Make your line long enough so that it will extend beyond the parallel sides of the tray when the tray is in position.
Step 2: As part of your procedure, make a light ray beam follow the line as it enters the tray. Trace the path of the beam coming out of the tray.
Step 3: Compare the traced path of the exiting beam to the position of the line you drew earlier.
10. Sketch diagrams as outlined in steps 4 (a), (b), and (d) of "Procedure," or study the following diagrams.
The path of a light ray going through an empty tray is as follows.
Path of the Light Through a Tray
Going Further
You have likely observed a glass prism or a glass ornament that projects rainbow colours onto a wall. The colours appear due to refraction. The study of refraction led to the discovery that white light, such as sunlight, is actually a mixture of colours. Isaac Newton demonstrated this.
Do you want to learn more about white light, colour, and the interaction of light with coloured surfaces? Then read pages 228 to 230 of the textbook.
12. To test your understanding of the concepts in this lesson, answer questions 1 to 5 of "Topic 3 Review" on page 206 of the textbook.
Going Further
Practise your investigative skills as you learn more about light. Complete questions 8 and 9 on page 206 of the textbook. Note that you will need your instructor's approval to actually do an investigation.
Looking Back
In this lesson you observed that light is refracted when it passes through a boundary, a surface, or an edge between two optically different, transparent substances. In other words, a ray of light is bent. From observations, you reasoned that moving from a less dense substance to a denser substance causes light to bend toward the normal line as it slows down. Moving from a more dense substance into a less dense substance, light bends away from the normal line as it speeds up.
The rays of light changed direction. They were bent by the water. The bent ray got past the rim, allowing you to see the coin again. A ray diagram shows this.
1. The pencil was lying flat on the table, with the ends visible on either side of the glass. Light from the ends travelled only through the air. Light from the middle of the pencil travelled through air, plastic, water, plastic, and back into the air. This light did not travel in a straight line. You know this because the middle part of the pencil appeared bent, as in the following sketch.
2. Light from the bottom of the pencil travelled through water, plastic, and air. The light did not travel in a straight line. When the light moved from the water into air it was bent. This makes the pencil appear to be broken at the water's surface, as in the sketch on the left.
3. Light travels through three different media in this activity - these are air, plastic, and water. The effect of plastic is not noticed because the cup is not very thick.
Note: You may want to compare viewing the pencil through the empty plastic cup and through an empty, but thick, drinking glass.
4. The path of light changes direction during refraction. The image of the object appears to be bent or broken.
refraction: the change in direction of a ray of light when it passes from one medium into another due to a change in the speed of the light