How Does the Focal Length of a Lens Vary with Red and Green Light?

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SUMMARY

The discussion focuses on the variation of focal length in lenses when using red and green light, emphasizing the relationship between wavelength and refractive index. Participants mention the equation 1/u + 1/v = 1/f, which relates object distance (u), image distance (v), and focal length (f). The inverse proportionality of refractive index (n) to wavelength indicates that shorter wavelengths, such as green light, will be refracted more than longer wavelengths like red light. Users share their experimental setups involving LEDs, lenses, and measurement tools to explore these optical properties.

PREREQUISITES
  • Understanding of basic optics principles, including focal length and lens behavior.
  • Familiarity with the lens formula: 1/u + 1/v = 1/f.
  • Knowledge of the relationship between wavelength and refractive index.
  • Experience with experimental setups involving light sources and measurement tools.
NEXT STEPS
  • Research the effects of wavelength on refractive index in different materials.
  • Learn about experimental methods for measuring focal lengths using various light sources.
  • Explore graphical analysis techniques for plotting object and image distances.
  • Investigate the behavior of lenses with different types of light (e.g., LED vs. incandescent).
USEFUL FOR

Students and educators in physics, optical engineers, and hobbyists conducting experiments with lenses and light to understand optical phenomena.

Ahem
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"To use a graphical approach to determine whether there is a difference between the focal length of a lens when used with red and green light."

What would I expect to see?

What sort of results do you think I will get?

What would be the variable?

I need to use the equation 1/u + 1/v = 1/f can anyone help in explaining it?

Has anyone done anything similar before?

Thanks for any help.
 
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I can't remember the exact equation, but I do recall that the refractive index, n, of an object is inversely proportional to the wavelength (i.e. as the wavelength decreases, the amount the light is refracted by increases).

Have you been given any more information then that that you've given in your post? Because, otherwise, I can't see how to do more then give a vague approximation of what would happen.
 
Well, using a suitable lens I had to take measurements over a range of object and image distances to help me plot the graph. I've got some results, but I don't know if they're correct or suitable.


I'm not sure what you mean in the first half of your post.
 
My results are all ****ty, say for instance I wanted to make up some results. I'm using an LED with a green and red light, a lens, a white block (improvised as a screen to project the image -red or green light-) and a metre ruler. What sort of results do you think I would get or see?
 
Anybody??
 

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