School Science Project Help

Hello everyone, I was wondering if I could bother you for some quick opinions. My daughter is learning about optics at school and needs to put together a project that demonstrates how a lens works. She had an idea of shining a laser pointer through a convex lens and inserting a sheet of paper at various points to show how the beam diverges and then creates a focal point. Before we go out and spend money for the components, could you answer a few questions?

1. Is the attached diagram an accurate description of what would happen?
2. In those divergent areas, would you guess that the beam profile would be "fuzzy"? My fear is that there will be a consistent red dot over the entire length.
3. I've been looking for a smallish lense that might work. Would you have a suggestion for something to use with a red laser pointer rated at 5mW?
4. We obviously don't want to catch anything on fire. Would you guess that the focal point would heat up? I can't find a laser pointer less than 5mW.

Thanks in advance for your time. My apologies is these questions are muddled or have been posted before (I did a search. Really, I did!)

You can find cheap 5mw modules on ebay with drivers attached. Just supply the required voltage and youre off! Find one witha focusable lens. The only problem is that the beam comes out fairly small so the difference between the lens and focal point would be hard to demonstrate to a large audience. Past the focal point you could move the paper inches or even feet away and clearly see the beam incrising in size as it diverges out.

Excellent, I'll do an Ebay search. Thank you for your time!

Does the project have to be a lens?

The reason I ask is there is a pretty easy and cheap way to make a big impact with refraction in water.

Fill a small container with flat sides with water and add enough milk to make it murky.

Then shine a laser through it - you will clearly see the beam, and it will be refracted by the water making an angle to the glass when compared to the entrance angle.

See this...
Index of Refraction Pre-lab

If you have to do the lens, it will be more difficult as the 5mw beam is very hard to see regardless due to its low power... you may want to make a bit of steam or glycerin fog to make the beam more visible - and then you can visually appreciate the convergence and divergence of the beam...

Edit: I just realized you were going to use paper to show the beam-spot... it may be easier if you first diverge the beam and then re-converge it, since the spot size is so small to start with, it wont converge much.. See the image below:

Optics by Christopher Purdy, on Flickr