PHYS 1600 Lecture Notes - Lecture 1: Triangular Prism, Molecular Cloud, Binary Star

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4 Feb 2016
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Chapter 6- light
1 When a rod of metal is heated intensely, its predominant colour will
A) remain predominantly red as the intensity of light increases.
B) change from red through orange to white and then to blue.
C) change from blue through white, then orange, and finally red, when it becomes
red-hot at its hottest.
D) be white, all colours mixed together, as the intensity of light increases.
2. To a physicist, a blackbody is defined as an object that
A) always emits the same spectrum of light, whatever its temperature.
B) reflects all radiation that falls upon it, never heating up and always appearing
black.
C) always appears to be black, whatever its temperature
D) absorbs all radiation that falls upon it.
3. The Sun's spectrum peaks in the yellow-green region of the spectrum (i.e., this
region is the most intense part of its spectrum). The spectrum of Rigel (the star in the
knee of Rigel) peaks in the short-wavelength end of the visible spectrum. Compared
to the Sun, Rigel is
A) cooler and redder.
B) cooler and more white.
C) hotter and redder.
D) hotter and more white
4. What property of helium allowed scientists to first discover its existence?
A) It accumulates inside meteoroids (fragments of rock and iron orbiting the Sun that,
when they fall to the Earth, are known as meteorites).
B) It refuses to combine chemically with other elements.
C) It absorbed light at certain wavelengths that were not characteristic of any element
known at that time.
D) It was characteristically found in rocks containing radioactively decaying
elements, such as uranium.
5. What is a diffraction grating?
1
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A) A flat, rectangular array of closely spaced photosensitive cells
B) A piece of glass with thousands of closely spaced, parallel grooves
C) An array of many radio telescopes used to observe a single source simultaneously
D) A triangular prism of solid glass used to disperse light into its colours
6. The spectrum of sunlight, when spread out by a spectrograph, has what
characteristic appearance?
A) A continuous band of colour, crossed by innumerable emission lines
B) A continuous band of colour, crossed by innumerable dark absorption lines
C) A series of separate emission lines, characteristic of many elements, that overlap in
certain regions of the spectrum to produce short continuum segments
D) A continuous and uniform band of colour from violet to deep red
7. The spectrum of a star shows an equivalent set of dark absorption lines to those of
the Sun, but with one exception: Every line appears at a slightly longer wavelength,
shifted toward the red end of the spectrum. What conclusion can be drawn from this
observation?
A) A cloud of cold gas and dust surrounds the star and is absorbing light from it.
B) The star is moving rapidly toward the Earth.
C) The temperature of the star's surface is higher than that of the Sun.
D) The star is moving rapidly away from the Earth.
8. An astronomer measures the spectrum of a star and finds a spectral line at 499 nm
wavelength. In the laboratory, this spectral line occurs at 500 nm. According to the
Doppler effect, this object is
A) moving toward the Earth at 1/500 the speed of light.
B) moving away from the Earth at 1/500 the speed of light.
C) moving toward the Earth at 499/500 the speed of light.
D) moving away from the Earth at 499/500 the speed of light.
9. The radial velocity of a star or other object is measured by
A) measuring the change in the angular diameter of the object.
B) watching the object move compared to the background stars.
C) measuring the intensity of the light in different regions of the blackbody curve
D) observing the Doppler shift of spectral lines in the light from the object.
10. An example of an object that emits no radiation at all is
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A) any object at a temperature of 0 K.
B) any object at the temperature of outer space.
C) any blackbody at any temperature.
D) any object made of ice, at 0°C.
1. Light is a wave phenomenon involving the propagation of an oscillating electric
(and magnetic) field. These are called Electromagnetic waves.
2. Electromagnetic waves are differentiated only by their wavelength. The
electromagnetic spectrum spans a vast range of wavelength from the longest
radio waves to the shortest gamma rays. The range of visible light is from 670 nm
(red light) to 400 nm (blue-violet light).
3. When radiation is spread out according to its wavelength we have a "spectrum" of
the radiation. Various devices such as a prism or a diffraction grating can be used
to produce a spectrum. The instruments that effect this analysis are called
"spectrometers" or "spectrographs".
4. Virtually everything we know about astronomical objects comes from a study of
their light spectra. In particular we can determine
a. The temperature of the object.
b. The chemical composition of the object
c. The radial velocity of the object
5. Hot dense objects emit continuous spectra. Glowing rarefied gases emit line
spectra or exhibit absorption spectra when a continuous source illuminates them.
6. When radiating objects move toward an observer the radiation wavelength is
observed to be shifted to a shorter wavelength (blue shift). When it moves away
the wavelength is observed to be shifted to a longer value (red shift). This is
known as the Doppler effect.
Chapter 7- The sun
1. What is the Sun's photosphere?
A) The envelope of convective mass motion in the outer interior of the Sun
B) The lowest layer of the Sun's atmosphere
C) The middle layer of the Sun's atmosphere
D) The upper layer of the Sun's atmosphere
2. The approximate temperature of the visible surface of the Sun is
3
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