# Homework Help: Suitable experiment for 16-year-olds? Topic: Light

1. Sep 29, 2005

### quaanaa

Suitable experiment for 16-year-olds? Topic: "Light"

Does anyone have a suggestion for a good physics experiment for first-year high school students (in Denmark), which has to do with light? It doesn't matter what, it only needs to be "fleshy" enough to write a three-page report about, include a series of concrete measurements which can be used in calculations, and NOT include any trigonometry (since they haven't learned to use that yet).

This last requirement sadly throws any spectral measurements and other grating/interference experiments.

I would be very appreciative of any ideas you may have.

2. Sep 29, 2005

### Pengwuino

ooo... things were looking great until you said "Not include any trigonometry".

3. Sep 29, 2005

### Danger

Maybe report on the effects (observed) of various shapes of lenses? Make a telescope or microscope? Burn down the school with a magnifying glass?

4. Sep 29, 2005

### blimkie

yea i just satrted typing a huge lsit out for you then i reread and saw the no trig part

5. Sep 29, 2005

### blimkie

Perhaps you could just use fibre optic cables there always neat. Or the old shine the lazer through water vapor or smoke chalk dust etc. I have no idea about experiemnts that dont invlove trig tho. Just tell them how fast light travels and put them to work fidning the time it takes for light to travel various distances! that ell keep em busy

6. Sep 30, 2005

### quaanaa

That's not an experiment, that's just solving problems.

7. Sep 30, 2005

### quaanaa

Not bad. They could measure focal lengths and show the rule that you just add the dioptries of different lenses to find the cumulative effect...

8. Sep 30, 2005

### quaanaa

Exactly :) That's the challenge....

9. Sep 30, 2005

### andrevdh

quaanaa,
you could investigate how a convex lens forms images with light. Learn how it magnifies images and determine the focal length of a convex lens. You need a convex lens, a metre ruler, 2 corks (large diameters) and four pins.

Stick two of the pins in one of the corks. Position them 2 centimeters apart on top of the cork. The pins should be positioned in front of the lens with the connecting line perpendicular to the axis of the lens. Cut the other cork in half lengthwise. Stick the other two pins into the tops of the two halves. Align these two pins with the images on the other side of the lens. You need to look through the lens on the other side while moving your head closer and further away from the lens. The idea is to look in the air for the images.Once you have located them and positioned the two pins (on the cork halves) to coincide with these you need to measure the object (u), image (v) and separation (d) distances. Tabulate these. Move the object (the cork with the two pins in it) by a few centimeters closer (or further) to the lens and repeat the process. Do this another three times. The magnification of the image is given by:
$$m=\frac{v}{u}$$
which you calculate from half of the separation between the 2 pins behind the lens. Plot a graph of the magnification against the image distance. From the lens formula it can be shown that:
$$m=\frac{v}{f}-1$$
The slope of your graph will therefore be:
$$slope=\frac{1}{f}$$
and the intercept on the v axis will be f also. At unit magnification (v = u) we can show by using the lens formula that:
$$v=u=2f$$
another value for f can thus be obtained from the graph:
$$f=\frac{OB}{2}$$
Calculate the average of the focal lenghts obtained in these ways.

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Last edited: Nov 29, 2006