Berkeley College Lab Report Summary Essay

Dispersion, Color Observation, and Emission of LightE = hν, Energy and frequency are directly proportional. The higher the energy the higher
the frequency and vice versa.
Theory:
The electromagnetic spectrum includes all radiation from radio, microwave, infrared, visible
light, ultraviolet, X-rays, and gamma rays. The sun emits radiation in the UV, Visible and IR
(infrared region). Each section is measured in nanometers indicating the LENGTH of the
radiation emitted. The shorter the wavelength the greater the energy The longer the wavelength
the deeper the penetration. Visible light (the light that reaches the human retina is from 400nm
(blue) to 700 nm (red). Each spectrum of light has a different biological activity. In this lab, we
will study spectrum and atomic emission of the visible light.
Our eyes are ideally adapted for the light produced by the sun during daylight hours. Human eye
have receptors that received light for day vision (photopic – 555nm max), night vision (scotopic 500nm max) and circadian response (480 nm). (White light from the sun is a composite of all the
visible frequencies.)
We can simplify the radiation curve of the visible light emitted by the sun and divide it into three
regions: a) highest energy (blue), the lowest wavelength b) medium energy (green), the middle
wavelength and c) lowest energy (red), the highest wavelength. Three types of day
photoreceptors (cones) in our eyes perceive color. When all three types of cones are stimulated
equally, we see white.
By adding various amounts of red, green, and blue colors to which each of our three types of
cones are sensitive, we can produce any color in the spectrum.
Color dispersion experiment
Using the light box, fit the slit former that gives a wide beam.
Aim a single wide beam through the equilateral prism and adjust the prism so that the maximum
deflection of the ray is obtained. The refracted (deflected from the original path) beam should be
colored. To see it place a white paper in the path of the ray.
Note that the original beam from the light box is white and when it passes through the prism it is
dispersed into various colors such a spread of color caused by the dispersion of white light is
called a Spectrum.
If more than red and blue are present (and they should be) make a list of the order in which they
appear: violet, blue, green, yellow, orange, red
Which color is refracted (deflected) the least? red
Which color is refracted the most? violet
Which color has the lowest frequency? red
The lowest energy? red
Which has the highest frequency? violet
The highest energy? violet
Is there a correlation between the energy the amount of refraction and the energy (or frequency)
of the light?
What is the correlation? The higher the energy the higher refraction
Color observation experiment (mixing colored lights)
For this part of the experiment, use the end of the light box as well as the side positions. You will
use the red, green and blue filters provided. For best results, place filters vertically in the path of
the beam.
1. 1) With the lamp off, place the red filter on the left side position, the green in the center
position and the blue in the right position.
2. 2) Close the hinged side mirrors
3. 3) Turn the lamp on
4. 4) Use white paper in the path of the beam. You should see a green light
5. 5) Open the left side. Red light should appear. As red and green lights are mixing,
what is the resultant color? RED + GREEN = yellow
6. 6) Close the left side and open the right side. Blue light should appear. As blue and
green lights are mixing, what is the resultant color? BLUE + GREEN = teal
7. 7) Now open the two sides simultaneously (approximately 45 degree angle each).
You should see at least 5 colors. What is the color that results when the three beams
overlap?
RED + GREEN + BLUE = white light
Emission spectra
Every molecule has a fingerprint of light emission after it has been excited. This is similar to the
bar codes on food in the supermarket. The bars are related to the number and position of
electrons in their orbits.
When an atom is excited with light energy, its go to the higher energy orbit and then it will “fall
back” to its original orbit. This “fall back” pattern (black spectral lines) are an absolute
“fingerprint” – something that is distinctive for that chemical element and none other. This is
why we can look at the light of our sun and the light from very distant stars and identify the
elements present in those stars.
I) We will take glass tubes containing various gases at very low pressure, and we will heat the
tubes. Because the gases are at low pressure, the gas molecules will not interact with each other
significantly. The gas molecules will absorb energy from their surroundings and some of their
electrons will increase in energy. When the electrons “fall back” to their lower energy, they
release photons. Falling back from a higher energy level leads to the release of higher energy
(shorter wavelength) photons. The wavelength of light released in this type of experiment is
called the “emission spectrum”. We can tell the wavelength of a photon by the color of light
associated with the photon. The observation that atoms in these experiments released photons
only of particular, discrete energies (rather than every possible energy) led to our understanding
of quantum mechanics and the structure of atoms.
We will use spectrometers to separate photons of different wavelengths and to measure the
wavelengths of light emitted in these experiments.
Write down the emission wavelengths of 3 different emission spectra in the visible range. For
each heated gas, give the color to the naked eye and the colors and wavelengths as diffracted by
the spectrometer.
HYDROGEN – PINK
Violet 420
Blue 480
Red 660
HELIUM – YELLOW ISH
Blue 460
Yellow 580
Red 770
Green 500
MERCURY – BLUE
Violet 460
Green 560
Yellow 580
Red 680
1) Do you think you would be able to use a spectrometer to distinguish Hydrogen from
Deuterium? Explain.
I am not sure but maybe because of different colors?
2) What determines the energies of emitted light from a gas?
Wavelenght. The longer the wavelength the less the energy.
3) What determines if emission will be in the visible, UV, or infrared spectrum?
Position of the spectrum.