|Difficulty: Advanced 9|
|Cost ($): 250|
Time required:1 day to prepare, 1 day for observation
Availability of materials:Scuba diving gear, a boat, and lighting equipment may be rented from a scuba diving rental shop
Be extremely careful to ensure the safety of all participants. Life jackets must be worn at all times, and adult involvement is mandatory. The involvement of a qualified and experienced scuba diver is absolutely necessary.
The color of the red and yellow balls seems to reduce in intensity as the balls are submerged deeper into the water.
Colors and water depth
Each color that we see in the color spectrum has its unique wavelength. Violet and blue have shorter wavelengths. The wavelengths gradually increase for green, yellow, orange and red. Red has the longest wavelength.
The colors that we see on an object are due to the light that is being reflected by the surface of the object. A red object will absorb all other colors but red. Red light is reflected off the surface and our eyes detected the color. A white object will not absorb any light and instead reflects all the colors while a black object will absorb all the colors and reflect none of the light.
When light penetrates water, some parts of the spectrum of light will be absorbed by water. This causes perceived color changes. Given perfect conditions, red which has one of the longest wavelengths, will be absorbed first by water. Blue and violet lights have shorter wavelengths and will penetrate deeper into water. This means that a red object may appear to be black in color, in deep water because red light is of a wavelength that is more readily absorbed by water
The materials required for the experiment:
- A boat and life jackets
- 1 set of scuba diving gear
- An experienced scuba diver
- 1 high resolution underwater camera with flash
- 1 underwater handheld flood light
- 1 depth gauge
- Colored metal balls – red, yellow, green and blue
- A black marker pen
1. For this experiment, the independent variable is the color of the ball (i.e. red, yellow, green and blue) and the depths at which the observations are made – 5 meters, 10 meters, 15 meters and 20 meters. The dependent variable is the perceived color of the ball at different depths. This is determined by taking a photo of the balls at different depths. The constants (control variables) are the clarity of the water, whether fresh water or seawater is used, the time of the day and the weather.
2. The services of an experienced scuba diver are required, for this science project. Arrangements are made with the diver to rent a boat and the required diving gear. Select a diving location that has a depth of over 20 meters.
3. On the day of the experiment, a trip to the chosen diving location is made with the diver. Using the black marker pen, the colors of the metal balls are written on its surface. The diver is instructed to take photographs of the metal balls using the underwater camera at depths of 5 meters, 10 meters, 15 meters and 20 meters. He should also make a mental note of what he sees at each depth.
4. The photos are developed and the colors of the balls at different depths are determined. The results as to whether the colors are still visible at various depths are recorded in the table given below.
It is observed that the color of the red and yellow balls cease to be visible at depths of 15 meters and 20 meters under water.
The hypothesis that the intensity of the color of the red and yellow balls seem to lessen as they go deeper into the water is proven to be correct.
There are a lot of factors that determine the visibility of colors in water. The time of the day will determine the angle that sunlight will enter the water surface. Light penetration takes place most during noon when the sunlight is perpendicular to the water surface. The weather will also determine the amount of sunlight and light penetration in the water. A floodlight can be used to augment the lighting required for this science project.
Try to repeat this project using balls of different colors such as violet, brown, white, orange and pink.
Would the results of this experiment differ if it were done in fresh water instead of sea water.
What if it were performed at night, in the absence of any natural sunlight.
Effects of water depth on color visibility - http://www.educatedangler.com/index.php?option=com_content&view=article&id=921
Order of loss of visibility of colors under water with depth - http://www.madsci.org/posts/archives/2000-02/951747486.Ph.r.html