Properties of Light
Danielle Silverstein PHY 101 Section 10497 March 4, 2013 Light up this World Purpose: In this lab experiment, LED lights will be used to show how when E&M radiation is absorbed, the energy is converted to heat. A drop of isopropyl alcohol will absorb light energy of different colors, and the evaporation rate of the alcohol will be measured. The key to this lab is the evaporation rate is directly related to the energy of the light shining on the drop.
Materials:
- LEDs and circuits (from previous lab)
- Pipette (or eyedropper)
- Rubbing alcohol Index card
- 9-volt battery
- Flashlight
- Stopwatch
Small cardboard box (shoe box) Procedures: A three-sided enclosure from the cardboard box was made. This created a location for applying light from the LED to the drop of alcohol while minimizing the effect of air currents on the evaporation rate. The eyedropper was used to place a single drop of isopropyl alcohol on an index card within the enclosure. The same size drop was used each time the step was repeated. The time it takes for the drop to evaporate without the LED present was recorded.
The dark spot on the card caused by the alcohol was no longer visible. A flashlight was used to help with the observance of the dark spot. The evaporation time was recorded. The same procedure was repeated for the different colored LEDs over the alcohol drop. The current through each LED and the distance from the LED to the drop of alcohol was the same for each run. The procedure for each color of LED was repeated at least 10 times and an average time of evaporation for each color was calculated. A graph of evaporation time versus frequency of the LED was then made. Data:
Time it took to dry the drop (minutes)
| With no light= 10 minutes | Red(minutes) | Green(minutes) | Blue(minutes) | ||
| 1 | 4:43 | 5:15 | 3:30 | ||
| 2 | 4:49 | 3:59 | 3:14 | ||
| 3 | 5:03 | 4:55 | 4:07 | ||
| 4 | 5:23 | 3:48 | 3:13 | ||
| 5 | 4:00 | 4:26 | 3:26 | ||
| 6 | 5:04 | 4:47 | 3:37 | ||
| 7 | 4:35 | 4:20 | 3:25 | ||
| 8 | 5:25 | 3:54 | 3:10 | ||
| 9 | 4:30 | 5:05 | 3:40 | ||
| 10 | 4:45 | 4:15 | 3:56 |
Results: The results show that red had the lowest frequency and used the least amount of energy, green was in the middle of the two other colors with a frequency of 6. ·10-14 and blue had the highest frequency of 6. 67·10-14 Conclusion: Light is range of the electromagnetic spectrum detectable by the naked human eye. The spectrum also includes radio waves all the way up to gamma rays, and light falls about in the middle. Electromagnetic radiation combines both particles and waves in nature. Electromagnetic radiation can also be described in terms of a stream of photons. These are massless particles traveling with wavelike properties at the speed of light. For example, the changing electric and magnetic fields in space form electromagnetic waves (Library Thinking Quest). The colors on the spectrum vary from red to violet.
The red light has a lower energy than the violet light that’s at the end of the spectrum. The frequency of the light increases as the color of the light changes from red to violet. Wavelength and frequency are inversely proportional, which causes the wavelength to decrease as the color changes from red to violet (Hewitt, pg. 520). Depending on the color of the light, the wavelength can range from 7×10-5 cm (red) to 4×10-5 cm (violet), but all electromagnetic radiation travels at the speed of light. The frequency of the light, which is the number of wavelengths per seconds is calculated using the equation C=LN. L is the wavelength, N is the frequency, and C is the speed of light (Library Thinking Quest).
From the observations collected, the red LED light took the longest to dry the drop of alcohol and the blue dried it the fastest. Since the red light is on the lower end of the electromagnetic spectrum is used the lowest amount of energy. Just by looking at the brightness of the light, this conclusion was made but reassured after doing some research. The red light was very dim and faint compared to the brightness of the green and the blue. The blue was the brightest of the lights. This light used the most energy and is one of the farthest on the spectrum beside violet. Since the frequency of light increases as the color of light moves down the spectrum, the red light has the smallest frequency of 4. 2*10-14, green has middle frequency of 5. 66*10-14 and blue has the largest frequency of 6. 37*10-14. The frequency is directly proportional to the energy produced by each of the light, which is shown in the graph above. The blue light had the highest frequency and that used the most energy. The red LED used the least amount of energy because it had the lowest frequency. The greater the frequency caused the alcohol to dry faster since it used more heat (energy) at one time. Light energy and frequency are directly related in the real world also. Typically since red lights have less energy than blues lights, blue objects are said to be hotter.
In 1923, American astronomer Edwin Hubble (1889-1953) made an astounding discovery. As Hubble observed, the light waves from distant galaxies are shifted to the red end, and he reasoned that this must mean those galaxies are moving away from the Milky Way. These observations concluded that something that showed red was moving away from its observer. The laws of thermodynamics state that where heat is involved, the movement is always away from an area of high temperature and toward an area of low temperature. Heated molecules that reflect red light are areas that are moving toward an area of low temperature. Molecules of low temperature reflect bluish or purple light because the tendency of heat is to move toward them.
Fire, for example, it lets off heat to keep people warm. The color of fire is mostly red and orange. These colors are at the lower end of the spectrum of light. The reason why fire is the color red is because; red gives off the lowest amount of energy because it has the lowest frequency. Fire can be used in many different ways in the world without using mass amount of energy to heat things up. As mentioned in the lab from last week, the alligator clips caused a lot of issues with holing the connections together. A better material would be the connection covers where the wires go inside a little tube and are squeezed together at each end to insure security.
When the light went out due to the connection, it caused created a longer time for the alcohol drop to dry. This created some error in the experiment with the time and the overall average.
References:
- Hewitt, P. G. (1998). Chapter 23,24. Conceptual physics (8th ed. , pp. 494-550). Reading, Mass. : Addison Wesley.
- Lesson 9 Electricity. (n. d. ). PHY 101 .
- Retrieved February 9, 201328, 2013, from https://www. riolearn. org/content/phy/phy101/PHY101_INTER_0000_v4/lessons/lesson08. shtml? encrypted-sectionid=am5lN0s1VHdrNkRZdEdaK3ZBR3dSdz09
- “The Physics of Light: What Is Light?. ” ThinkQuest : Library. N. p. , n. d. Web. 19 Mar. 2013.
