.Drawing Ray Diagrams: Tips & Tricks for Solving Problems

In summary, the conversation is about drawing ray diagrams for a lab assignment and the person is seeking tips and resources for doing so. They mention a specific problem involving a converging lens and ask for help with understanding the focal length and determining the location and magnification of the image. The expert confirms that the person should draw the three principal rays and provides a helpful website for doing so. They also clarify the meaning of focal length and explain how to use the lens equation to find the location of the image.
  • #1
GingerBread27
108
0
I'm having a lot of trouble drawing ray diagrams (this is for a lab assignment). If anyone could give me some tips or links to websites that are helpful in teaching how to draw ray diagrams that would be great. One example of a problem is: A 1-cm tall arrow (the object) is placed 2 cm to the left of a converging lens having a 7 cm focal length. Show all three pricipal rays. Is the image real/virtual?Erect of inverted? Measuring from diagram determine the location and magnification of the image.

Now I think that I draw an upright arrow, 1 cm tall, to the left of the lens and then 7 cm to the right of the lens i draw another arrow? Is it upside down, larger/smaller? I have no idea what I'm doing and the write up for the lab is not helpful. Please help! thanks
 
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  • #2
You draw the three principle rays emanating from the tip of the 1-cm arrow you drew (which is your object). If you draw them correctly, they will meet at the point where the image of that arrow tip is. You'll be able to tell whether the image is real, inverted, magnified, just by looking at your (carefully drawn) diagram.

Here's a site that tells you how to draw those rays: http://www.glenbrook.k12.il.us/gbssci/phys/Class/refrn/u14l5da.html
 
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  • #3
For the problem I posted above would it be correct to do:

(1/do)+(1/di)=(1/f)=== (1/2)+(1/di)=(1/7), to get a di=-14/5=-2.8 cm, putting the image at 2.8 cm to the right of the lens?
Or am I completely clueless as to what focal length truly means, I thought it meant that the image was 7 cm from the lens.
 
  • #4
Or am I completely clueless as to what focal length truly means, I thought it meant that the image was 7 cm from the lens.

No, that's not what it means. The focal length is the property of the lens itself.

to get a di=-14/5=-2.8 cm, putting the image at 2.8 cm to the right of the lens?

Notice that [itex]d_i[/itex] is negative. This means that the image is virtual. So, the image is to the left of the lens.
 
  • #5
GingerBread27 said:
For the problem I posted above would it be correct to do:

(1/do)+(1/di)=(1/f)=== (1/2)+(1/di)=(1/7), to get a di=-14/5=-2.8 cm, putting the image at 2.8 cm to the right of the lens?
Your use of the lens equation is correct, but your interpretation of the minus sign is not. (See Berislav's comments.) The sign convention says that a positive image distance is to the right of the lens; a negative image distance, to the left.

Or am I completely clueless as to what focal length truly means, I thought it meant that the image was 7 cm from the lens.
A focal length of 7cm means that parallel rays will be focused at the focal point, which is 7cm past the lens; it describes how much the lens converges (or diverges) the light that goes through it. (The shorter the focal length, the more powerful the lens.) Where the image is formed depends on (1) where you put the object and (2) the focal length of the lens. To find where the image is, use the lens equation (just as you did).
 

1. What is the purpose of drawing ray diagrams in science?

Ray diagrams are used to visually represent the path of light in a given situation. They help scientists understand and predict how light will behave, making it easier to solve problems and make predictions about the behavior of light in various scenarios.

2. How do I draw a ray diagram?

To draw a ray diagram, start by identifying the object, the light source, and the location of the lens or mirror. Then, draw a straight line from the object to the lens or mirror, representing the incident ray. Next, draw a line from the lens or mirror to the focal point, representing the refracted or reflected ray. Finally, draw a line from the focal point to the image, representing the final position of the light rays.

3. Can I use ray diagrams to solve problems involving lenses and mirrors?

Yes, ray diagrams are an essential tool for solving problems involving lenses and mirrors. By accurately drawing the path of light, you can determine the size and position of images formed by lenses and mirrors, as well as the properties of the images (e.g. whether they are real or virtual, upright or inverted).

4. Are there any tips or tricks for drawing ray diagrams?

Yes, there are a few tips and tricks that can make drawing ray diagrams easier. First, remember that light travels in a straight line, so your incident and reflected/refracted rays should always be straight lines. Additionally, remember that the angle of incidence is equal to the angle of reflection, and the angle of incidence plus the angle of refraction always equals 90 degrees.

5. Can I use ray diagrams for other types of waves besides light?

While ray diagrams are most commonly used for light, they can also be used to represent the behavior of other types of waves, such as sound waves or water waves. However, keep in mind that the principles of reflection and refraction may differ for these types of waves, so the diagrams may look slightly different.

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