Measuring Wavelength
Aron Fristoe, Educator, MathScience Innovation Center
Developed with funding from the MathScience Innovation Center. Adapted from
the “LED Color Strip Kit” available through the Institute of Chemical Education
http://ice.chem.wisc.edu/
Questions
What is the difference between an LED light and incandescent light? How is
IR light different from visible light? What is a diode?
Materials
For each group of students:
 LED Color Strip/Clipboard
 9-volt battery
 500 lines/mm linear diffraction grating slides
 Meter stick
 Ruler
 White paper
Safety
Use voltage probe properly.
Procedure
1. Stand the LED Color Strip upright. Place the diffraction slide at the edge
of the table and, using a meter stick, place the LED Color Strip 50 cm
away from the diffraction slide. Look through the diffraction slide with it
up to your eye and view the LED Color Strip. Sketch what you see on the
cm paper showing where the colors appear.
2. Have one partner look through the diffraction slide. (Make sure the
distance from the diffraction slide and the LED Color Strip remains at 50
cm). Record the brightest area of the streak that corresponds to the
distance where the color appears on the cm paper in column A below.
3. Calculate the wavelength of each light. To do this, make sure the
LabQuest or calculator is set to radians and follow these steps:
a. Divide the distance you recorded above by 50 (the distance your LED
Color Strip was from the diffraction slide). Record in Column B in the
chart below.
b. Calculate the sine of Column B. Record in Column C in the chart
below.
c. Multiply Column C by 2000. This number converts the measurement
to nanometers (nm). Record this number in Column D.
The Color of Quantum
http://MathInScience.info
©MathScience Innovation Center, 2012
Data/Analysis
1.
2.
Color
A
Distance
observed on
Ruler (cm)
B
Column A
divided by 50
cm
C
sine (column
B)
D
Column C x
2000
Red
Orange
Yellow
Green
Blue
Questions
1. What relationship can you generate from the colors and their
corresponding wavelengths?
2. If these were to be graphed, what kind of graph would we see (straight
line, linear, curve)?
Extension
Round your calculation to the 10’s place and record it on the LED Data Table
under “Calculated Wavelength (nm)” in Activity: Finding Voltage and
Crunching Numbers.
References
Institute of Chemical Education, “LED Color Strip Kit Activity Manual”:
http://ice.chem.wisc.edu/
MathScience Innovation Center
Information on educational programs available to students, teachers and
school divisions, and procedures for registering for programs.
http://msinnovation.info
The Color of Quantum
http://MathInScience.info
©MathScience Innovation Center, 2012
Measuring the Wavelengths of Light Key
1. Stand the LED Color Strip upright. Place the diffraction slide at the edge of the table and, using a meter
stick, place the LED Color Strip 50 cm away from the diffraction slide. Look through the diffraction slide
with it up to your eye and view the LED Color Strip. Sketch what you see below showing where the
colors appear.
Blue
Green
Yellow
Orange
Red
Infrared (no visible
light)
2. Have one partner look through the diffraction slide. (Make sure the distance from the diffraction slide
and the LED Color Strip remains at 50 cm.) Mark where the brightest area of the streak that
corresponds to the color appears on the paper Column A below.
3. Calculate the wavelength of each light. To do this, MAKE SURE YOUR LABQUEST IS SET TO RADIANS and
follow these steps.
a. Divide the distance you recorded above by 50 (the distance your LED Color Strip was from the
diffraction slide). Record in Column B below.
b. Calculate the sine of Column B. Record in Column C below.
c. Multiply Column C by 2000. This number converts the measurement to nanometers (nm).
Round your calculation to the 10’s place and record it on the LED Data Table under “Calculated
Wavelength (nm).”
Color
A
Distance
observed on
Ruler (cm)
B
Column A
divided by 50 cm
C
sin (column B)
D
Column C x 2000
11.5
0.230
0.228
460
14.1
0.282
0.278
560
15.1
0.302
0.297
590
15.6
0.312
0.307
610
16.7
0.334
0.329
Blue
Green
Yellow
Orange
Red
660
Record these values on the next page in
the LED Data Table under “Measured
Wavelength.” (Extension activity)
The Color of Quantum
http://MathInScience.info
©MathScience Innovation Center, 2012