Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: Focal length vs wavelength

Learn more physics!

Most recent answer: 03/13/2013
Q:
we know that focal length increases with increase of wavelength of light. can we use different color zero watt bulb as the source of light for the convex lens and prove the above statement?
- megha (age 11)
chennai, tamilnadu,india
A:
Hi Megha,

The difference in focal length for red versus blue light is fairly small, so you'll have to do the measurement carefully. Ideally, you would have a red laser beam and a blue laser beam, since these beams don't spread out as quickly before hitting your lens, and they have nice focuses that are easy to measure. Since you probably just have light bulbs, take care to keep everything except the wavelength exactly the same between your two tests. If you bump anything between taking the measurements, it might not work.

Even if you are very careful, it might be tricky.

Good luck! Let us know if it works.
David

(published on 03/13/2013)

Follow-up on this answer.