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Chapter 17: Lesson 3 - Ray Diagrams
Chapter 17: Lesson 3 - Ray Diagrams
Ray Diagrams for Concave Mirrors
Ray Diagrams for Concave Mirrors
Concave mirrors can form both read and virtual images. We will use ray diagrams to show how concave mirrors form images and how to locate and describe those images.
To easily understand how ray diagrams works with curved mirrors, we use an arrow to represent the object and the image. The arrow tells us the magnitude (the size) and the direction of the object/image.
There are two rays that we draw to find the image in a curved mirror. Look at the pictures below to see the blue ray as it starts from the object and is reflected off of the mirror and the green ray as it starts from the object as is reflected from the mirror.
You start drawing the first ray from the top of the object parallel to the principal axis.
That first ray is then reflected through the mirror's focal point.
The second ray is just the opposite to the first ray. You start from the top of the object and align your ruler through the focal point. Your ray is drawn until it reaches the mirror.
The ray is then reflected parallel to the principal axis.
Drawing the Image
Drawing the Image
The image is found where the two reflected rays intersect. The image is drawn from the principal axis to where the two reflected rays intersect. You can see the image here in red.
Describing the Image
Describing the Image
To describe the image, we use the acronym LOST.
L stands for location. This is where the image is located. We describe the image in relation to the center of curvature, C and the focal point, F.
O stands for orientation. The orientation is where we see if the image is erect (right side up) or inverted (upside down) as compared to the object.
S stands for size. We describe the size of the image as compared to the size of the object. If the image is smaller than the object or if the image is larger than the object.
T stands for type. The image is either a real image or a virtual image. A real image is where the reflected rays converge. A virtual image is where the reflected rays do not converge and we have to draw dotted lines behind the mirror to show where the rays appear to converge.
This is a concave ray diagram where the object is beyond the center of curvature. The image in this ray diagram (the green arrow) is...
L: Between C and F
O: Inverted
S: Smaller
T: Real Image
This is a convex ray diagram. The image in this ray diagram (the blue arrow on the right) is...
L: Behind the mirror
O: Erect
S: Smaller
T: Virtual Image
Ray Diagrams for Convex Mirrors
Ray Diagrams for Convex Mirrors
Convex mirrors form virtual images. We will use ray diagrams to show how convex mirrors form images and how to locate and describe those images.
Things are a little different from the concave mirrors because the focal point is behind the mirror.
You start drawing the first ray from the top of the object parallel to the principal axis.
You then line up your straight edge between the point where the first ray hit the mirror and the focal point. The red line is where you would line your ruler up with. That first ray is then reflected through the mirror's focal point, away from the mirror.
The second ray is just the opposite to the first ray. You line up your straight edge between the top of the object and the focal point. The red line is where you would line your ruler up with. Your ray is drawn from the top of the object until it reaches the mirror.
The ray is then reflected parallel to the principal axis.
This picture shows the two rays. The blue ray and the green ray will never intersect, so there is one more step that you have to do to find out where they APPEAR to converge.
You take the reflected rays and, using a dotted line, you extend the reflected ray behind the mirror. We use a dotted line to represent the light is not really going behind the mirror.
Drawing the Image
Drawing the Image
The image is found where the two reflected rays intersect. The image is drawn from the principal axis to where the two reflected rays intersect. You can see the image here in red. It is a virtual image because the light only appears to converge there. It doesn't actually do so.
Check Your Understanding:
Check Your Understanding:
Click on the down arrow when you have your answer to check to see if you are correct.
Describe the purple image in this ray diagram of a concave mirror. The object is beyond the center of curvature.
This image is between C and F, inverted, smaller, and real.
2. Describe the red image in this ray diagram of a convex mirror.
The image is behind the mirror, erect, smaller, and virtual.
Practice Drawing Ray Diagrams
Practice Drawing Ray Diagrams
Click here for the paper that I use in the video. As you watch this video, pause it and try to draw the rays and describe the image on your own.
It is important that you know how to draw the four different concave mirror cases and the one convex mirror case. Use the LOST acronym to help you describe the image.
These are ALL the cases for concave mirrors (4 cases) and convex mirrors (1 case). If you can draw these, you will be all set!
Remember there are more practice ray diagrams under Chapter 17 Resources. Practice the drawing and describing the image and then see if your answer matches my answer.
Before the Next Class Period
Before the Next Class Period
Practice these Ray Diagrams Before Class!
Practice these Ray Diagrams Before Class!
Click on the picture to take you to the ray diagrams that I will be going over the next time we have class. Remember, you need to try the ray diagrams on your own to see where you make your mistakes if you want to learn how to do the ray diagrams on your own.
You have finished Lesson 3!
You have finished Lesson 3!
Be sure to head over to google classroom and fill out the exit pass.
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