The Relationship between Distance and Light Intensity

Abstract

The purpose of my Science Fair Project is to find out whether distance affects the light intensity of different sources of light such as a flashlight and laser pointer.

In each experiment, I put a light probe in clamp stand on one end of 2 meter sticks and a light source in other clamp stand at the other end of the meter sticks. For every 10 cm interval, I got a light intensity reading. I repeated this 4 times for each light source.

My hypothesis was correct. The flashlight decreased in intensity with distance. The laser stayed about the same intensity as I predicted. The light waves of a laser travel in parallel lines so the intensity should not decrease. The light intensity of a flashlight decreases in a curve and never should approach zero.

Problem

What is the relationship between light and distance?

I hope to get an understanding of light intensity and the effect of distance on it. This problem is important because if we know that distance does or does not have a affect on the light intensity of a flashlight or laser, we could find out if that is why some planets get sun and some don’t.

Background Information - What are Lasers?

Light is a swift messenger that comes to us from tiny invisible worlds of atoms from the enormous worlds of distant stars. A laser is a device that produces an intense beam of light of one color. White light consists of a combination of wavelengths all traveling randomly. Lasers produce coherent light. This means that it is of only one wavelength with waves and crests all traveling together. Lasers are used for many things: making accurate measurements, surgery, reading CDs, and reading the UPC codes on products.

A flashlight is a portable electric light in a metal fiber or plastic case. There is a tiny wire in the bulb of a flashlight that is lighted by being brought into contact with the electric from one or more dry cell batteries.

Hypothesis

I predict that the light intensity of the flashlight will decrease but will never hit the X- axis. I think this because the brightness will never get to zero because the light source will never turn off to get to zero. This is what I think will happen to the results of the flashlight section of my Science Fair Project.

I predict that the light intensity of the laser will stay somewhat the same. I think this because the beam will not spread out into a light cone like the flashlight. The waves and crests will all travel together in a parallel path.

Materials

TI-83 Calculator

CBL w/ Light Probe

2 meter sticks

laser

flashlight

Procedure

1. Clamp light probe in clamp stand.
2. Clamp flashlight in other clamp stand.
3. Put two meter sticks (front-to-back and cm side up) in between the two clamp stands.
4. Set up the light probe program on the TI-83 calculator.
5. Make sure the room is completely dark and no light is shining directly on light probe by getting a zero value with lights off.
6. Put the light end of the flashlight on the end of the meter stick (still in clamp stand over top meter stick.)
7. Make sure that the flashlight is directly shining on the light probe. Adjust to get highest reading for each distance.
8. Get a reading from the CBL at the 200 cm point.
9. Then move the flashlight (still in clamp) to the 190 cm point (make sure the flashlight is still lined up with the light probe).
10. Keep this procedure going for every 10cm and get a reading.
11. Once you have gotten through all the points with the flashlight, repeat the steps 1-11 for the laser in the place of the flashlight.
12. Repeat the experiment with the laser & flashlight four times each. (Make sure the light is shinning on the light probe, and that you are recording your data.)
13. Now see if you can find any relationship between the variables.

Data

See http://www.qacps.k12.md.us/cms/sci/PROJBD.HTM#data