Visible light meets clear glass
Cell phone signals pass through walls
Blue light hits a red sweatshirt
Visible light does not pass through a black wall
Reflection or scattering
Red light hits a red sweatshirt
White light hits a white piece of paper
Light comes from a light bulb
Light comes from your computer screen
Process of Science: The Solar Spectrum
The prism bends different wavelengths of light by different amounts, causing the white light from the Sun
to spread out into a rainbow of colors. Absorption features appear as dark lines against the brighter
background of the spectrum.
Wavelength × frequency = speed of light
o The key relationship is wavelength × frequency=speed of light. The speed of light through space is
always the same, so when wavelength goes up (longer), frequency must go down (lower), and vice
o The visible light with the longest wavelength is red.
To remember this, think about the fact that infrared light has longer wavelength than visible
light and is called infrared because it is close to red light in the spectrum.
Red light is the longest wavelength visible light, and longer wavelength means lower
frequency (because wavelength×frequency=speed of light).
Which of the following best describes why the Sun’s spectrum contains black lines over an underlying
o The Sun’s hot interior produces a continuous rainbow of color, but cooler gas at the surface absorbs
light at particular wavelengths.
o The Sun’s spectrum is an absorption line spectrum, which is produced when continuous light from a
hot source (the Sun’s interior) passes through a cooler cloud of gas (the gas that makes up the Sun’s
Notice that the Sun’s spectrum appears brightest (or most intense) in the yellow-green region. This fact
tells us __________.
o The approximate temperature of the Sun’s surface
o One of the two laws of thermal radiation (Wien’s law) states that the peak wavelength of a
spectrum is directly related to an object’s temperature. A peak at yellow-green wavelengths
corresponds to a temperature of about 5800 K.
A spectral line is produced when __________.
o an electron in an atom, ion, or molecule gains or loses a precise amount of energy
o an electron in an atom, ion, or molecule gains or loses a precise amount of energy Suppose we want to know what the Sun is made of. What should we do?
o Compare the wavelengths of lines in the Sun’s spectrum to the wavelengths of lines produced by
chemical elements in the laboratory.
o Each chemical element (or ion or molecule) produces a unique set of spectral lines; the wavelengths
of these lines can be measured in the laboratory. If the Sun's spectrum contains the set of lines for
some particular element, we conclude that the Sun contains that element. We determine the Sun’s
overall chemical composition by examining all the lines in its spectrum.
Any spectrum can be displayed either in photographic form as shown to the left or as a graph. Which of the
following graphs could represent a portion of the Sun’s visible light spectrum?
o The smooth part of the curve represents the graph of the background rainbow of color; the dips in
the curve represent the black lines where light is missing from the rainbow
Three Basic Types of Spectra
Recall that one of the laws of thermal radiation states that a higher-temperature object emits photons with
higher average energy (Wien’s law). This law is