Astronomy Chapter 5

Suppose you look at a spectrum of visible light by looking through a prism or diffraction grating. How can you decide whether it is an emission line spectrum or an absorption line spectrum?

An emission line spectrum consists of bright lines on a dark background, while an absorption line spectrum consists of dark lines on a rainbow background.

Suppose we want to know what the Sun is made of. What should we do?

Compare the wavelengths of lines in the Sun's spectrum to the wavelengths of lines produced by chemical elements in the laboratory-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.

Which of the following procedures would allow you to make a spectrum of the Sun similar to the one shown, though with less detail?

Pass a narrow beam of sunlight through a prism-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.

Which of the following best describes why the Sun's spectrum contains black lines over an underlying rainbow?

The Sun's hot interior produces a continuous rainbow of color, but cooler gas at the surface absorbs light at particular wavelengths.-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 visible surface).

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?

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.

Suppose you watch a leaf bobbing up and down as ripples pass it by in a pond. You notice that it does two full up and down bobs each second. Which statement is true of the ripples on the pond?

They have a frequency of 2 hertz.

Which of the following best describes the fundamental difference between two different chemical elements (such as oxygen and carbon)?

They have different numbers of protons in their nucleus.

Study the graph of the intensity of light versus wavelength for continuous spectra, observing how it changes with the temperature of the light bulb. 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 illustrated by the fact that for a higher temperature object, the graph peaks at __________.

a shorter wavelength

If we say that a material is opaque to ultraviolet light, we mean that it _________.

absorbs ultraviolet light

What type of visible light spectrum does the Sun produce?

an absorption line spectrum

The absorption line spectrum shows what we see when we look at a hot light source (such as a star or light bulb) directly behind a cooler cloud of gas. Suppose instead that we are looking at the gas cloud but the light source is off to the side instead of directly behind it. In that case, the spectrum would __________.

be an emission spectrum

From shortest to longest wavelength, which of the following correctly orders the different categories of electromagnetic radiation?

gamma rays, X rays, ultraviolet, visible light, infrared, radio

The spectra of most galaxies show redshifts. This means that their spectral lines _________.

have wavelengths that are longer than normal

Blue light has higher frequency than red light. Thus, blue light has:

higher energy and shorter wavelength than red light.

Suppose you know the frequency of a photon and the speed of light. What else can you determine about the photon?

its wavelength and energy

In the illustration of the solar spectrum, the upper left portion of the spectrum shows the __________ visible light.

lowest frequency-Red light is the longest wavelength visible light, and longer wavelength means lower frequency (because wavelength x frequency = speed of light

Click "show" for the emission line spectrum, then click "choose gases" and study the emission line spectrum for neon. The neon "OPEN" sign appears reddish-orange because __________.

neon atoms emit many more yellow and red photons than blue and violet photons

Thermal radiation is defined as _________.

radiation with a spectrum whose shape depends only on the temperature of the emitting object

Notice that the Sun's spectrum appears brightest (or most intense) in the yellow-green region. This fact tells us __________.

the approximate temperature of the Sun's surface-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.

Suppose you want to know the chemical composition of a distant star. Which piece of information is most useful to you?

the wavelengths of spectral lines in the star's spectrum