Station # 1. Reflection off of a rough surface. The Law of reflection. Problem: How is light reflected off of a flat smooth surface?

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Gertrude McGee
5 years ago
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1 In your notes Station # 1 LABEL ME When a light ray strikes an object and bounces off Ex. Mirror Reflection off of a smooth surface Reflection off of a rough surface The Law of Reflection states that the angle of incidence = angle of reflection The Law of reflection Problem: How is light reflected off of a flat smooth surface? Data Table: Angle of Incident Angle of Reflection Procedure: 1. Use the protractor and align the laser light to strike the mirror at 20 observe the angle of reflection. incident on the mirror as shown in the chart above. Remember this angle is from the normal. 2. Move the laser to the other angles listed and observe the angle of the reflected beam.

2 In your notes Station # 2 YOU WILL GET THIS AT STATION 3 Label the picture based on the speed of light as it enters each medium Light rays bend when passing from one medium to another change speed Bends towards the normal Bends away from the normal Disappearing penny Problem: Why does an object seem to disappear when placed under a beaker of water? Procedure 1: 1. Place a penny on the table. 2. Place the empty beaker on top of the penny and observe. 3. Place the beaker with water on top of the penny and observe. 4. Look at the penny through the sides of the beaker. Problem: What causes a penny at the bottom of a glass to suddenly appear as water is added to the glass? Procedure 2: 1. Get two cups. Fill one with water and leave the other one empty. 2. Place a penny in the empty cup. The penny should be positioned so that it is on the side closest to your partner. Your partner should barely be able to see the edge of the penny in the cup. 3. Slowly pour water from the second cup into the cup with the penny until your partner tells you that he or she can see the penny completely. Your partner should not move while you are pouring.

3 Station # 3 READ BELOW AND RECORD THE NECESSARY INFORMATION IN ORDER FOR YOU TO UNDERSTAND THE INDEX OF REFRACTION Summarize the diagram below - indicating which medium is the most dense and at what point light is traveling the fastest. When light passes from one medium to another, the light changes speed, and when it changes speed, it changes direction a little bit. The degree to which the light changes direction is called the Index of Refraction. The Index of Refraction Magic Show Problem: If two objects have the same index of refraction what will happen to the light ray? Procedure 1: 1 st look at the bottom of the glass rod it should be close to invisible! Next, swirl the glass rod in the beaker (GENTLY) does the second beaker become visible? WHY DID THAT HAPPEN? You see a glass object because it both reflects and refracts light. When light traveling through air encounters a glass surface at an angle, some of the light reflects. The rest of the light keeps going, but it bends or refracts as it moves from the air to the glass. When light passes from air into glass, it slows down. It s this change in speed that causes the light to reflect and refract as it moves from one clear material (air) to another (glass). Every material has an index of refraction that is linked to the speed of light in the material. The higher a material s index of refraction, the slower light travels in that material Wesson vegetable oil has nearly the same index of refraction (n) as Pyrex glass (n = 1.474). Different types of glass have different indices of refraction. In Wesson oil, Pyrex disappears. Procedure 2: Try putting the paper with arrows and the word WOW behind (about 6-8 inches) the glass of water. Do the arrows change direction?

4 Station # 4 interaction between light and matter that causes light to change direction. Look at the pictures and descriptions listed summarize why the sky is blue HERE Look at the pictures and descriptions listed summarize why sunsets are red and orange HERE Why is the sky blue? Problem: Why does the sky appear blue? Procedure: 1. Using the flashlight on your phone shine the flashlight over the top, try looking from the top, the side and then from the bottom. 2. Now shine your flashlight from the side, change your point a view again looking from the top, side and bottom. Can you see a blue sky? A red sunset? 1 st 2 nd ORANGE BLUE

5 Station # 5 Properties of plane mirrors It s true that plane mirrors produce simpler images than curved mirrors, but they certainly aren t trivial. Ask a group of people who have never studied optics where they think the image produced by a plane mirror is located and you ll get three responses. Some will say, On the mirror surface, of course. Others will say, In front of the mirror s surface, of course. Still others will say, Behind the mirror s surface, of course. People tend to be emphatic about what they know to be true. But all three locations can t be right. Decide as a group where the image produced by a plane mirror is located. Procedure: 1. Line the mirror up on the line marked XY. 2. Place the object about 7 cm in front of the mirror. Where does the image appear? 3. Move the object closer to the mirror. Where does the image appear? 4. Place the card with the word in front of the mirror. What happens? **BASED ON YOUR OBSERVATIONS FILL OUT THE INFORMATION IN YOUR NOTES** Are light rays actually crossing where the IMAGE appears? Mirrors produce VIRTUAL IMAGES. Virtual images are images that are formed in locations where light does not actually reach. Light does not actually pass through the location on the other side of the mirror; it only appears to an observer as though the light is coming from this location. Whenever a mirror (whether a plane mirror or otherwise) creates an image that is virtual, it will be located behind the mirror where light does not really come from. *** Fill in your notes and answer Example 1***

6 Station # 6 Mirror vocabulary Beginning a study of spherical mirrors demands that you first become acquainted with some terminology that will be periodically used. Principal axis Center of Curvature Vertex Focal Point Radius of Curvature Focal Length If a concave mirror were thought of as being a slice of a sphere, then there would be a line passing through the center of the sphere and attaching to the mirror in the exact center of the mirror. This line is known as the principal axis. The point in the center of the sphere from which the mirror was sliced is known as the center of curvature and is denoted by the letter C in the diagram below. The point on the mirror's surface where the principal axis meets the mirror is known as the vertex and is denoted by the letter A in the diagram below. The vertex is the geometric center of the mirror. Midway between the vertex and the center of curvature is a point known as the focal point; the focal point is denoted by the letter F in the diagram below. The distance from the vertex to the center of curvature is known as the radius of curvature (represented by R). The radius of curvature is the radius of the sphere from which the mirror was cut. Finally, the distance from the mirror to the focal point is known as the focal length (represented by f). Since the focal point is the midpoint of the line segment adjoining the vertex and the center of curvature, the focal length would be one-half the radius of curvature. ON YOUR PAPER LABEL THE DIAGRAM USE THE READING TO DEFINE EACH OF THE TERMS LISTED. The focal point is the point in space at which light incident towards the mirror and traveling parallel to the principal axis will meet after reflection. The diagram at the right depicts this principle. In fact, if some light from the sun were collected by a concave mirror, then it would converge at the focal point. Because the sun is such a large distance from the Earth, any light rays from the sun that strike the mirror will essentially be traveling parallel to the principal axis. As such, this light should reflect and pass through the focal point.

Station # 7 Properties of concave mirrors If the inside of the spherical surface is the reflecting surface, the mirror is said to be concave or converging.

7 Station # 7 Properties of concave mirrors If the inside of the spherical surface is the reflecting surface, the mirror is said to be concave or converging. They form upright, enlarged images, and are therefore useful in makeup application or shaving. They are also used in flashlights and headlights because they project parallel beams of light, and in telescopes because they focus light to produce greatly enlarged images. They are referred to as converging because they collect light from a large area into a small area (telescope) and they gather light into beams (Car headlights, or spotlight). Concave mirrors form both real and virtual images. Real images are always inverted and can be projected on a screen. PROCEDURE: 1. Using the concave mirrors provided find a photo on your phone TURN YOUR BRIGHTNESS ALL THE WAY UP. It also helps to have a photo of one object (like a selfie) see if you can get the photo projected onto the wall using the mirror. Try to get the photo as clear as possible. (See diagram below although I have found phones to work better than outside) Is the photo upright or inverted? 2. Hold the mirror close in front of you. What do you see? Compare the size of this image with the image in the plane mirror. Answer questions on your lab sheet. 3. Now hold the mirror as far away far you as you can,i.e. with your arm fully stretched. What do you see? 4. Using the mirrors on the table move back and forth seeing if your image is inverted (flipped upside down) and if so is it clear? (focused) What do you have to do for the image to be upright?

Station # 8 Properties of convex mirrors A convex mirror is sometimes referred to as a diverging mirror because as light rays are reflected off of the mirror they are spread outward.

After reflection, the light rays diverge; subsequently they will never intersect on the object side of the mirror.

Compare the size of this image with the size of the image in the plane and concave mirrors.

8 Station # 8 Properties of convex mirrors A convex mirror is sometimes referred to as a diverging mirror because as light rays are reflected off of the mirror they are spread outward. The diagram at the right shows four incident rays originating from a point and incident towards a convex mirror. These four rays will each reflect according to the law of reflection. After reflection, the light rays diverge; subsequently they will never intersect on the object side of the mirror. For this reason, convex mirrors produce virtual images that are located somewhere behind the mirror. PROCEDURE 1: Hold a convex mirror close in front of you. What do you see? Compare the size of this image with the size of the image in the plane and concave mirrors. Using the large mirror in the front of the room, stand back at least 10 feet, describe the type of image produced. Move closer to the mirror and describe if there are any changes in the image. Using the convex mirrors provided find a photo on your phone TURN YOUR BRIGHTNESS ALL THE WAY UP. It also helps to have a photo of one object (like a selfie) see if you can get the photo projected onto the wall using the mirror. (This may not be possible) Describe the images formed on your lab sheet.

9 Station 9: Vocabulary and Protractor Practice REAL IMAGES images formed where light rays actually cross. are always inverted (flipped upside down) Used in movies projected onto screen. VIRTUAL IMAGES rays do not actually converge to form image. Cannot be projected. images are formed where light rays appear to have crossed. are always upright

Converging Lenses. Parallel rays are brought to a focus by a converging lens (one that is thicker in the center than it is at the edge).

Converging Lenses. Parallel rays are brought to a focus by a converging lens (one that is thicker in the center than it is at the edge). Chapter 30: Lenses Types of Lenses Piece of glass or transparent material that bends parallel rays of light so they cross and form an image Two types: Converging Diverging Converging Lenses Parallel rays