Transcript Quiz 7 Solutions

Frequency and Wavelength
• How are frequency, wavelength, and speed
related for electromagnetic radiation in empty
space?
– speed = frequency x wavelength, where speed is the
speed of sound.
– speed = frequency/wavelength, were speed is the
speed of light.
– speed = frequency x wavelength, where speed is the
speed of light.
– speed = wavelength/frequency, were speed is the
speed of light.
– speed = wavelength/frequency, were speed is the
speed of sound.
Frequency and Wavelength
• How are frequency, wavelength, and speed
related for electromagnetic radiation in empty
space?
– speed = frequency x wavelength, where speed is the
speed of sound.
– speed = frequency/wavelength, were speed is the
speed of light.
– speed = frequency x wavelength, where speed is the
speed of light.
– speed = wavelength/frequency, were speed is the
speed of light.
– speed = wavelength/frequency, were speed is the
speed of sound.
Bullets
• Suppose someone is shooting bullets at
you with a machine gun that fires a bullet
every 10 seconds. If you run toward the
stream of bullets, the frequency at which
you get hit will
– stay the same
– increase
– decrease
Bullets
• Suppose someone is shooting bullets at
you with a machine gun that fires a bullet
every 10 seconds. If you run toward the
stream of bullets, the frequency at which
you get hit will
– stay the same
– increase
– decrease
Photons
• Suppose that a star was shooting green photons
at you. You measure the time between peaks in
the photon wave. If you are moving toward the
star, what happens to the time between wave
peaks in the photon wave? What will happen to
the color you see?
– I see the wave peaks more frequently. The photon
appears to be more blue.
– I see the wave peaks less frequently. The photon
appears to be more red.
– I see the wave peaks less frequently. The photon
appears to be more blue.
– I see the wave peaks more frequently. The photon
appears to be more red.
Photons
• Suppose that a star was shooting green photons
at you. You measure the time between peaks in
the photon wave. If you are moving toward the
star, what happens to the time between wave
peaks in the photon wave? What will happen to
the color you see?
– I see the wave peaks more frequently. The photon
appears to be more blue.
– I see the wave peaks less frequently. The photon
appears to be more red.
– I see the wave peaks less frequently. The photon
appears to be more blue.
– I see the wave peaks more frequently. The photon
appears to be more red.
Blackbody approximation
• One way of creating a blackbody is to (1)
create an empty ball out of iron (2) make
its interior rough and (3) drill a small hole
in it. If you shoot a photon into the hole,
when will it be emitted from hole?
• After one reflection.
• After a very, very long time.
• After two reflections.
• After three reflections.
Blackbody approximation
• One way of creating a blackbody is to (1)
create an empty ball out of iron (2) make
its interior rough and (3) drill a small hole
in it. If you shoot a photon into the hole,
when will it be emitted from hole?
• After one reflection.
• After a very, very long time.
• After two reflections.
• After three reflections.
Color and Temperature
• Why does an opaque and dense object (such as
metal) first glow white before it glows blue when
it is heated?
– Before the metal glows blue, it emits white photons
because this is the emission spectra of that metal at
that temperature.
– Because the metal is not a perfect blackbody.
– Because humans tend to associate cold with blue.
– As you heat the metal, its blackbody curve shifts until
the peak is at a green wavelength. What humans call
white corresponds to the special combination of
intensity of green photons along with fewer red and
blue photons that the blackbody curve specifies.
Color and Temperature
• Why does an opaque and dense object (such as
metal) first glow white before it glows blue when
it is heated?
– Before the metal glows blue, it emits white photons
because this is the emission spectra of that metal at
that temperature.
– Because the metal is not a perfect blackbody.
– Because humans tend to associate cold with blue.
– As you heat the metal, its blackbody curve shifts until
the peak is at a green wavelength. What humans call
white corresponds to the special combination of
intensity of green photons along with fewer red and
blue photons that the blackbody curve specifies.
Spectrum 3
• The image below is the spectrum discussed in
class. Suppose Earth's atmosphere contained
only nitrogen atoms. What would change?
– There would be fewer dips in curve C. The locations
of the dips would correspond to the location of the
empty spots in the spectra that one would measure of
light from a blackbody passed through a cloud of
nitrogen gas.
– The peak in curve B would be less pronounced.
– Curve B would look much more like curve C.
– All of the curves would increase in amplitude and their
peak location would shift to the left.
– All of the curves would increase in amplitude and their
peak location would shift to the right.
What will
the
spectrum
look like
here?
Absorption Spectrum
Earth’s atmosphere
Black lines in absorption
line spectrum will
appear as low points in
Energy Flux curve
Count photons
per second on
absorption line
spectrum and
translate to
Energy Flux.
Spectrum 3
• The image below is the spectrum discussed in
class. Suppose Earth's atmosphere contained
only nitrogen atoms. What would change?
– There would be fewer dips in curve C. The locations
of the dips would correspond to the location of the
empty spots in the spectra that one would measure of
light from a blackbody passed through a cloud of
nitrogen gas.
– The peak in curve B would be less pronounced.
– Curve B would look much more like curve C.
– All of the curves would increase in amplitude and their
peak location would shift to the left.
– All of the curves would increase in amplitude and their
peak location would shift to the right.
You ought to be in pictures
• How much larger is a raw image of
900x900 pixels than one with 300x300
pixels? That is, how many more pixels are
in the 900x900 image?
–9
– 42
–3
– 27
– 81
You ought to be in pictures
• How much larger is a raw image of
900x900 pixels than one with 300x300
pixels? That is, how many more pixels are
in the 900x900 image?
–9
– 42
–3
– 27
– 81
Driving on the lawn
• In the following image, what happens to the wheels when
they hit the grass, and why?
– The wheels turn as in case (a). When the leading wheel hits the
grass, it slows down while the trailing wheel keeps at the same
speed. While the trailing wheel is on the sidewalk, the axle turns
as shown in (a).
– The wheels turn as in case (a). When the leading wheel hits the
grass, it speeds up while the trailing wheel keeps at the same
speed. While the trailing wheel is on the sidewalk, the axle turns
as shown in (a).
– The wheels turn as in case (c). When the leading wheel hits the
grass, it slows down while the trailing wheel keeps at the same
speed. While the trailing wheel is on the sidewalk, the axle turns
as shown in (c).
– The wheels turn as in case (b). When the leading wheel hits the
grass, it slows down at the same rate as the trailing wheel. While
the trailing wheel is on the sidewalk, the axle turns as shown in
(a).
Driving on the lawn
• In the following image, what happens to the wheels when
they hit the grass, and why?
– The wheels turn as in case (a). When the leading wheel hits the
grass, it slows down while the trailing wheel keeps at the same
speed. While the trailing wheel is on the sidewalk, the axle turns
as shown in (a).
– The wheels turn as in case (a). When the leading wheel hits the
grass, it speeds up while the trailing wheel keeps at the same
speed. While the trailing wheel is on the sidewalk, the axle turns
as shown in (a).
– The wheels turn as in case (c). When the leading wheel hits the
grass, it slows down while the trailing wheel keeps at the same
speed. While the trailing wheel is on the sidewalk, the axle turns
as shown in (c).
– The wheels turn as in case (b). When the leading wheel hits the
grass, it slows down at the same rate as the trailing wheel. While
the trailing wheel is on the sidewalk, the axle turns as shown in
(a).
Chromatic aberration
• What causes chromatic aberration?
– The fact that all electromagnetic radiation travels at
the speed of light in a vacuum.
– The fact that when a light beam strikes a mirror, it is
reflected at the same angle with respect to the normal
as its incident angle.
– The fact that light at different frequencies bends a
different amount when it goes from air into glass.
– The fact that each photon has an energy that is given
by Plank's Law.
Chromatic aberration
• What causes chromatic aberration?
– The fact that all electromagnetic radiation travels at
the speed of light in a vacuum.
– The fact that when a light beam strikes a mirror, it is
reflected at the same angle with respect to the normal
as its incident angle.
– The fact that light at different frequencies bends a
different amount when it goes from air into glass.
– The fact that each photon has an energy that is given
by Plank's Law.
Light bending 2
• If white represents air and blue represents
water, which way does the beam go when
it enters the water?
–A
–B
–C
Bends toward the normal
Dashed line is path of line A if it does not b
normal
When a light ray goes from air
into glass (or water) it bends
toward the normal
Light bending 2
• If white represents air and blue represents
water, which way does the beam go when
it enters the water?
–A
–B
–C
Lens
• Suppose you have a single lens from a
pair of eyeglasses that is 3 inches in
diameter. How many more photons hit this
lens per second than would hit a lens that
is only 1.5 inches in diameter?
– 4 times
– 2 times
– 8 times
– 16 times
Lens
• Suppose you have a single lens from a
pair of eyeglasses that is 3 inches in
diameter. How many more photons hit this
lens per second than would hit a lens that
is only 1.5 inches in diameter?
– 4 times
– 2 times
– 8 times
– 16 times
Refraction
• When light is incident on a surface,
refraction occurs when
– it enters the second medium and changes
direction.
– it “bounces off” at an angle (measured from
the normal) equal to the incident angle.
– it enters the second medium and changes
frequency.
– it “bounces off” at an angle (measured from
the normal) greater than the incident angle.
Refraction
• When light is incident on a surface,
refraction occurs when
– it enters the second medium and changes
direction.
– it “bounces off” at an angle (measured from
the normal) equal to the incident angle.
– it enters the second medium and changes
frequency.
– it “bounces off” at an angle (measured from
the normal) greater than the incident angle.
Telescopes
• Why is the Hubble Space Telescope in
orbit of Earth?
– Maintenance on the telescope is easier to do
in Earth orbit than on the Earth’s surface.
– To detect X-rays, which cannot penetrate the
Earth’s atmosphere.
– To get away from human-generated
electromagnetic interference.
– To eliminate the distorting effect of the Earth’s
atmosphere.
Telescopes
• Why is the Hubble Space Telescope in
orbit of Earth?
– Maintenance on the telescope is easier to do
in Earth orbit than on the Earth’s surface.
– To detect X-rays, which cannot penetrate the
Earth’s atmosphere.
– To get away from human-generated
electromagnetic interference.
– To eliminate the distorting effect of the Earth’s
atmosphere.
Objective lens
• What is the primary purpose of the
objective lens in a telescope?
– To isolate visible light from other
electromagnetic radiation
– To magnify the image
– To gather light
– To correct for chromatic aberration
Objective lens
• What is the primary purpose of the
objective lens in a telescope?
– To isolate visible light from other
electromagnetic radiation
– To magnify the image
– To gather light
– To correct for chromatic aberration
Camera lens
• Why does a camera with a bigger lens give you
a more detailed image? Select the best answer.
– More photons are used to create the image. More
photons means more detail for the same reason you
could draw a more detailed object using many dots
versus fewer dots.
– Fewer photons are used to create the image. Fewer
photons means more detail because there is less
interference among photons.
– Fewer photons are used to create the image. Fewer
photons means more detail because there is less
chromatic aberration.
– More photons are used to create the image. More
photons means more detail because there is less
chromatic aberration.
Camera lens
• Why does a camera with a bigger lens give you
a more detailed image? Select the best answer.
– More photons are used to create the image. More
photons means more detail for the same reason you
could draw a more detailed object using many dots
versus fewer dots.
– Fewer photons are used to create the image. Fewer
photons means more detail because there is less
interference among photons.
– Fewer photons are used to create the image. Fewer
photons means more detail because there is less
chromatic aberration.
– More photons are used to create the image. More
photons means more detail because there is less
chromatic aberration.