PHYS 1260 EXAM 3 QUESTIONS WITH VERIFIED
ANSWERS
electromagnetic waves - Answers - - light is the only thing we can see
* originates from the accelerated motion of electrons
* electromagnetic phenomenon
- electromagnetic wave: made up of vibrating electric and magnetic fields
if an electron vibrates up and down 1000 times each second, it generates an
electromagnetic wave w/ a - Answers - frequency of 1000 Hz
electromagnetic spectrum - Answers - - classification of electromagnetic eaves
according to frequency
- lowest frequency of visible light we can see appears red
- highest frequency of visible light we can see appears violet
- higher frequency of light is ultraviolet -> more energetic and causes sunburns
- beyond are x-ray and gamma ray
- no sharp boundary b/w regions
the electromagnetic spectrum spans waves ranging from lowest to highest frequencies.
the smallest portion of the electromagnetic spectrum is that of - Answers - visible light
which of these is fundamentally different from the others?
A. Sound waves
B. light waves
C. radio waves
D. x-rays - Answers - Sound waves -> all are electromagnetic waves except sound
which is a mechanical wave
transparent materials - Answers - - light is transmitted similarly to sound
* both are vibrations due to a vibrating source
- how light penetrates transparent material such as glass:
* electrons or molecules in the glass are forced into vibration
* energy is momentarily absorbed and vibrates the electrons in the glass
* this vibrating electron either emits a photon (a corpsucle of light) or transfers the
energy as heat
- time delay b/w absorption and re-emission of energy of vibrating electrons results in a
lower average speed of light through a transparent material
- in glass, infrared waves, w/ frequencies lower than those of visible light, cause not only
the electrons but entire atoms or molecules to vibrate, increasing the temp of the
structure
- so we see that glass is transparent to visible light, but not ultraviolet and infrared light
- avg speed of light through different materials
, * vacuum -- c (300,000,000 m/s)
* atmosphere -- slightly less than c (but rounded off to c)
* water -- 0.75 c
* glass -- 0.67 c, depending on material
* diamond -- 0.41 c
strictly speaking, the photons of light incident on glass are - Answers - not the ones that
travel through and exit the other side --> the light that exits the glass is not the same
light that begins the process of absorption and re-emission
compared w/ the frequency of illuminating light on a sheet of transparent plastic, the
frequency of light that is transmitted - Answers - is the same --> speed of light in plastic
may vary, but the frequency transmitted doesn't
the avg speed of light is less in - Answers - glass
opaque material - Answers - - most things around us are opaque --> they absorb light
w/o re-emitting it
* books, desks, chairs, and people are opaque
- vibrations given by light to their atoms and molecules are turned into random kinetic
energy -- into internal energy
* these materials become slightly warmer
- metals
*light shining on metal forces free electrons in the metal into vibrations that emit their
own light as reflection
- Light incident on:
* dry surfaces bounces directly to your eye
* wet surface bounces inside the transparent wet region, and reaches your eye darker
than from a dry surface
- shadows
* a thin beam of light is often called a ray
* when we stand in the sunlight, some of the light is stopped while other rays continue in
a straight-line path
* we cast a shadow = a region where light rays do not reach
- either a large, far-away light source or a small nearby light source will produce a sharp
shadow
- a large, nearby light source produces a somewhat blurry shadow
- there is usually a dark part on the inside and a lighter part around the edges of a
shadow
* a total shadow = umbra
* partial shadow = penumbra
* a penumbra appears where some of the light is blocked but where other light fills it in
* a penumbra also occurs where light from a broad source is only partially blocked
eclipses - Answers - - solar eclipse = bc of the large size of the sun, the rays taper to
provide an umbra (total eclipse) and a surrounding penumbra (partial eclipse)
ANSWERS
electromagnetic waves - Answers - - light is the only thing we can see
* originates from the accelerated motion of electrons
* electromagnetic phenomenon
- electromagnetic wave: made up of vibrating electric and magnetic fields
if an electron vibrates up and down 1000 times each second, it generates an
electromagnetic wave w/ a - Answers - frequency of 1000 Hz
electromagnetic spectrum - Answers - - classification of electromagnetic eaves
according to frequency
- lowest frequency of visible light we can see appears red
- highest frequency of visible light we can see appears violet
- higher frequency of light is ultraviolet -> more energetic and causes sunburns
- beyond are x-ray and gamma ray
- no sharp boundary b/w regions
the electromagnetic spectrum spans waves ranging from lowest to highest frequencies.
the smallest portion of the electromagnetic spectrum is that of - Answers - visible light
which of these is fundamentally different from the others?
A. Sound waves
B. light waves
C. radio waves
D. x-rays - Answers - Sound waves -> all are electromagnetic waves except sound
which is a mechanical wave
transparent materials - Answers - - light is transmitted similarly to sound
* both are vibrations due to a vibrating source
- how light penetrates transparent material such as glass:
* electrons or molecules in the glass are forced into vibration
* energy is momentarily absorbed and vibrates the electrons in the glass
* this vibrating electron either emits a photon (a corpsucle of light) or transfers the
energy as heat
- time delay b/w absorption and re-emission of energy of vibrating electrons results in a
lower average speed of light through a transparent material
- in glass, infrared waves, w/ frequencies lower than those of visible light, cause not only
the electrons but entire atoms or molecules to vibrate, increasing the temp of the
structure
- so we see that glass is transparent to visible light, but not ultraviolet and infrared light
- avg speed of light through different materials
, * vacuum -- c (300,000,000 m/s)
* atmosphere -- slightly less than c (but rounded off to c)
* water -- 0.75 c
* glass -- 0.67 c, depending on material
* diamond -- 0.41 c
strictly speaking, the photons of light incident on glass are - Answers - not the ones that
travel through and exit the other side --> the light that exits the glass is not the same
light that begins the process of absorption and re-emission
compared w/ the frequency of illuminating light on a sheet of transparent plastic, the
frequency of light that is transmitted - Answers - is the same --> speed of light in plastic
may vary, but the frequency transmitted doesn't
the avg speed of light is less in - Answers - glass
opaque material - Answers - - most things around us are opaque --> they absorb light
w/o re-emitting it
* books, desks, chairs, and people are opaque
- vibrations given by light to their atoms and molecules are turned into random kinetic
energy -- into internal energy
* these materials become slightly warmer
- metals
*light shining on metal forces free electrons in the metal into vibrations that emit their
own light as reflection
- Light incident on:
* dry surfaces bounces directly to your eye
* wet surface bounces inside the transparent wet region, and reaches your eye darker
than from a dry surface
- shadows
* a thin beam of light is often called a ray
* when we stand in the sunlight, some of the light is stopped while other rays continue in
a straight-line path
* we cast a shadow = a region where light rays do not reach
- either a large, far-away light source or a small nearby light source will produce a sharp
shadow
- a large, nearby light source produces a somewhat blurry shadow
- there is usually a dark part on the inside and a lighter part around the edges of a
shadow
* a total shadow = umbra
* partial shadow = penumbra
* a penumbra appears where some of the light is blocked but where other light fills it in
* a penumbra also occurs where light from a broad source is only partially blocked
eclipses - Answers - - solar eclipse = bc of the large size of the sun, the rays taper to
provide an umbra (total eclipse) and a surrounding penumbra (partial eclipse)
