PHY 101 Section 10497
March 4, 2013
Light up this World
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.
* LEDs and circuits (from previous lab)
* Pipette (or eyedropper)
* Rubbing alcohol
* Index card
* 9-volt battery
* Small cardboard box (shoe box)
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.
|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 | | | | | | | | | | | | | | | | | | | | | |Frequencies(Hz): |4.3·10-14 |6.0·10-14 |6.67·10-14 | |...