Visible Light Waves
The visible spectrum from red (at left) to violet (at right).
Visible light waves are the only electromagnetic waves we can see. We see these waves as the colors of the rainbow.
Each color has a different wavelength. Red has the longest wavelength and violet has the shortest wavelength. When all
the waves are seen together, they make white light.
When white light shines through a prism, the white light is broken apart into the colors of the visible light spectrum.
Water vapor in the atmosphere can also break apart wavelengths creating a rainbow.
Each color in a rainbow corresponds to a different wavelength of electromagnetic spectrum.
What’s a Spectroscope?
A spectroscope works by breaking light into the wavelengths that make it up. Some spectroscopes are made of diffraction
grating- a material that has lots of little parallel lines that are approximately one wavelength apart. There may be 35,000 of
these little lines in one inch of the material. When light hits the lines, it bends. Different wavelengths (colors) of light bend
by different amounts, so it splits the light into its colors. Other spectroscopes are made of prisms- as light passes through
the glass, the different wavelengths slow down by different amounts and are bent into their colors. Scientists can tell the
elements present in a star by looking at its light through a spectroscope. Each element will have its own unique spectral
lines of color, just as people each have a unique fingerprint.
So when you hold your spectroscope up to a light…
The spectroscope will separate light into its component colors by refraction, deflecting the longer wavelength (red) light
more than the shorter wavelength (blue/violet) light. Each wavelength has a different color, so you see a rainbow. With the
spectroscope you can see which wavelengths are present, and how bright each is. Let’s observe & record our findings.
1. Which light source allowed you to see the most different colors of the visible spectrum? Why do you think this?
2. In terms of wave energy, why did the instructions say NOT to choose the sun for this activity?
3. Why exactly does most light appear white yet have a rainbow of colors when you look through the spectroscope?