Download of light - Nutley Public Schools

Physics - Dr. Naumoff
Review – Chapters 25-29.
Name_________________________________
Date _________________________________
To be shown to your instructor at the end of the period.
1.
(Chapter 25) In the picture below
a. What is the length labeled “a” called?
_____Wavelength
(or Period if x-axis in time)
b. What is the length labeled “b” called? _____
Wavelength
(or Period if x-axis in
time)
c. What is the length labeled “c” called?
______Amplitude
d. What is the point labeled “d” called?
______Trough
e. What is the point labeled “e” called?
_______Crest
2.
A wave is generated by a source with a frequency of
30Hz. The distance between wave crests is 0.25m.
What is the speed of the wave? Please show all work
and units.
V=f*λ
V = 30 * .25 = 30/4 = 7.5 m/s
3.
How is the frequency of a wave related to its period?
The frequency of a wave is the inverse of its
period:
F = 1/T where T is the wave’s
period.
4.
How is the period of a wave related to its frequency?
The period of a wave is the inverse of its
frequency:
T = 1/F where F is the
wave’s frequency.
5.
What is the difference between a transverse wave and
a longitudinal wave?
In a transverse wave the medium (particles of matter
in the wave) move perpendicular to the motion of the
wave.
In a longitudinal wave the medium (particles of
matter in the wave) move in parallel to the motion of
the wave.
6.
(chapters 27 and 28)What does all electromagnetic
radiation have in common?
They are all transverse waves.
7.
What makes different types of electromagnetic
radiation different? _
The frequency and wavelength of the waves.
(Chapter 26)
8.
Define the following terms. Please use complete
sentences.
a. Beats: A throbbing in the loudness of sound
caused by interference when two tones of
slightly different frequencies are sounded
together.
b. Compression: A pulse of compressed air or other
matter.
c. Forced Vibration: The vibration of an object that
is made to vibrate by another vibrating object
that is nearby. The sounding board in a musical
instrument amplifies the sound through forced
vibration.
d. Infrasonic: The term applied to sound pitch too
low to be heard by the human ear, that is, below
20 Hz.
e. Natural Frequency: A frequency at which an
elastic object will vibrate. Minimum energy is
required to continue at that frequency. Also
called resonant frequency.
f. Pitch: The term that refers to how high or low
sound appear to be.
g. Rarefaction : A disturbance in the air (or matter)
in which the pressure is lowered. The opposite of
compression.
h. Resonance: A phenomenon that occurs when the
frequency of forced vibrations on an object
matches the objects natural frequency, resulting
in a dramatic increase in amplitude.
i. Ultrasonic: The term applied to sound pitch that
is too high to be heard by the human ear, that is,
above 20,000 Hz.
9.
What causes all sound waves?
Vibrations of material objects.
10.What
can sound waves travel through?
Mater that is solid, liquid or gas.
11.What
cannot sound waves travel through?
Empty Space or a vacuum.
12.Explain
what causes the sounding board on a guitar
to amplify the sound of the strings?
The strings cause a forced vibration in the sound
board resulting in an amplification of the sound
since the sound board has a greater surface area
than the strings.
13.Will
sound travel faster through air or steel? Why?
Steel because the molecules that need to vibrate
for sound to travel through are closer together in
steel than they are in air.
14.What
happens to the speed of sound in air as the air
temperature increases?
The speed of sound increases when the
temperature of the environment increases.
15.By
how much does the speed of sound increase for
every increase of 1oC in temperature?
The speed of sound increases in speed by
0.6 m/s for every 1 °C increase in temperature.
16.At
0 oC sound travels through air a 330 ms . How fast
does it travel at 5 oC?
V2 = V1 + 0.6*ΔT
= 330 m/s + 0.6 * 5 oC
= 330 + 3
= 333 m/s
17.A
device produces two tones, one at 400Hz and 1 at
410Hz. What is the beat frequency?
FB = F 2 - F1
FB= 410 – 400 = 10 Hz.
18.What
19.How
is important in creating resonance?
A forced vibration at the natural frequency
of the object.
do noise cancelling earphones work?
In coming noise is recorded , shifted by 180
degrees (or ½ wavelength) and then added to the
noise prior to reaching the speakers of the
headphones. This is an example of destructive
interference.
20.If
you have two identical sources producing the same
tone, why does destructive interference occur when
the path lengths from the two sources to the observer
differ by ½ of a wavelength?
Because the sign of the wave that is shifted by ½
wavelength becomes the exact opposite on the
un-shifted wave. When the two waves are added
they cancel each other (+1 +-1 =0).
Chapter 27
21.Define
the following terms. Please use complete
sentences.
a. Photon: A photon is a “particle” of light.
b. Electromagnetic wave : A wave that is partially
electric and partially magnetic and carries
energy. It is emitted by vibrating electrons.
c. Light-year: The distance light travels in one year
in a vacuum traveling at 3 x 108 meters/sec.
d. Opaque : The term applied to materials that
absorb light without reemission, and
consequently do not allow light through them.
e. Penumbra: A partial shadow that appears where
light from part of a source is blocked and light
from another part of the source is not blocked.
f. Polarization: The aligning of vibrations in a
transverse wave, usually by filtering out waves
of other directions.
g. Ray: A thin beam of light.
h. Shadow : A shaded region that results when light
falls on an object and thus cannot reach into a
region on the far side of the object.
i. Transparent : The term applied to materials that
allow light to pass through them in straight lines.
j. Ultraviolet: Electromagnetic waves of
frequencies higher than those of violet. Cannot
be seen by human eyes.
k. Umbra : The darker part of a shadow where all
the light is blocked.
22.What
does all electromagnetic radiation have in
common?
All electromagnetic radiation is composed of
transverse waves.
23.What
makes different types of electromagnetic
radiation different?
Electromagnetic radiation types differ by their
wavelength and frequencies.
24.How
does a penumbra occur?
As an object moves between a light source and a
viewing surface (screen) the object partially
blocks some of the light from that source.
However, some of the light from the source gets
around the object and fills in part of the shadow.
This results in a fuzzy shadow as opposed to a
distinct total shadow (umbra) when the light is
completely blocked by an object.
25.Describe
how ultraviolet electromagnetic radiation is
kept from passing through glass.
Light is transmitted through glass by exciting
electrons in the glass. Since the atoms in glass
have a natural frequency (they are resonant) in
the ultraviolet range, the atoms in the glass
vibrate without exciting the electrons. While
these atoms bump into each other they give up
their energy to each other Within the glass,
thereby warming it up not allowing these
frequencies pass through.
a. Explain why visible light passes through glass.
Light is transmitted through glass by
exciting the electrons in the atoms on the
surface of the glass. As these electrons emit the
light photons, they excite electrons on the inner
portion of the glass. This process continues until
the electrons in the atoms on the other side of
the pane of glass finally emit their photons into
the area enclosed completing the journey through
the glass. This process is also known as the
“Gulp and Burp” transmission of light.
26.Explain
why infrared electromagnetic radiation is
kept from passing through glass?
Infrared radiation vibrates not only the electrons,
but the entire structure of the glass. The vibration
of the structure increases the internal energy of it
warming it up thereby preventing these
frequencies from passing through.
27.How
do polaroid sunglasses block out glare caused
by horizontal surfaces?
Since light is composed of transverse waves
(waves whose particles vibrate perpendicular to
the direction of wave travel), polarized
sunglasses are made with filters that only pass
light that vibrate in the vertical direction.
28.What
causes all electromagnetic radiation?
The vibration of Electrons.
Chapter 28
1. Define the following terms. Please use complete
sentences.
a. Spectrum: For sunlight and other white light, the
spread of colors seen when light is passes
through a prism or diffraction grating.
b. Line spectrum: The pattern of distinct lines of
color corresponding to particular wavelengths
that are seen in a spectroscope when hot gas is
viewed.
c. White light: Light, such as sunlight, that is a
combination of all colors. Under white light,
white objects appear white and colored objects
appear in their individual colors.
d. Additive primary colors: Red, Green, Blue light.
When these three colors of light are added
together, they produce white light.
e. Complementary colors: Two colors of light
beams that when added together appear white.
f. Pigment : A material that selectively absorbs
colored light.
g. Scatter : To absorb sound or light and reemit it in
all directions.
h. Spectroscope: An instrument used to separate the
light emanating from a hot gas or other light
source into its constituent frequencies (colors)
i. Subtractive primary colors: The colors of
magenta, yellow and cyan. These are the three
colors most useful in color mixing by subtraction
(Paints and dyes).
2. Explain why the sky is blue?
The sky is blue because the O2 and N2 in the
atmosphere scatters the blue light the most during the
daylight hours.
3. Why is water greenish blue?
Water absorbs Red & infrared leaving cyan, that
color that appears greenish blue.
4. What is the brightest color in sunlight? YellowGreen because our eyes are most sensitive to that
portion of the visible spectrum.
5. What are the three primary colors of light addition?
Red, Green, Blue
6. What color is produced when red and blue lights
shine on a white surface? Magenta.
7. What is the complementary color of blue
Red.
8. What are the three paint colors useful for color
subtraction?
Magenta, Yellow and cyan.
9. What happens to most of the ultraviolet radiation that
comes to earth from the sun? Most of it is blocked by
the Earth’s atmosphere but some does get through
and reaches the surface.
10.
How does the daytime sky on the moon look?
Black
11. When a solid sample of an element is heated
until it glows what colors of light are given off?
First Infrared which we cannot see, then Red, then
Orange, then Yellow then bluish until it gives off
white light if the heat source is strong enough to raise
the object’s temperature high enough to emit white
light.
12. Explain why sunrises and sunsets are red. At the
time of sunrise and sunset, the sunlight must pass
through more and more atmosphere that scatters more
and more blue light leaving less and less to reach the
surface of the Earth. The light “left over to reach the
Earth’s surface” contains more red light as compared
to blue thereby turning the sky more red.
Chapter 29 –
1. Define the following terms. Please use complete
sentences.
a. Angle of incidence: The angle between an
incident ray of light and the normal
(perpendicular line) to a surface.
b. Angle of reflection : The angle between a
reflected ray of light and the normal
(perpendicular line) to a surface.
c. Critical angle: The minimum angle of incidence
for which a light ray is totally reflected within a
medium.
d. Dispersion : The separation of light into their
colors arranged according to their frequency by
interaction with a prism or diffraction grating.
e. Law of reflection : The Angle of Incidence for a
wave that strikes a surface is equal to the Angle
of Reflection for that wave. This is true for both
partially and totally reflected waves.
f. Normal: The line perpendicular to a surface that
the Angle of Incidence and Reflection is
measured from.
g. Reflection: The bouncing back of a particle or
wave that strikes the boundary between two
media.
h. Refraction: The change in direction of a wave as
it crosses the boundary between two media in
which the wave travels at different speeds.
i. Total internal reflection: The 100% reflection
(with no transmission) of light that strikes the
boundary between two media at an angle greater
than the critical angle.
j. Virtual image: An image formed through
refraction that can be seen by an observer but
cannot be projected on a screen because light
from the object does not come from to a focus.
k. Wave front: The crest, trough or any continuous
portion of a two- dimensional or threedimensional wave in which vibrations are all the
same way at the same time.
2. How does reflection of sound compare with the
reflection of light? Sound and light reflect in the
same way, they both obey the law of reflection.
Therefore, the angle of reflection for sound incident
on a boundary at the same angle of incidence as a
light wave would be identical to that of light.
3. Which color in the visible spectrum is bent the most
when it moves between different media? Violet.
4. Which color in the visible spectrum is bent the least
when it moves between different media? Red.
5. In the space below draw a diagram of a light ray
going from air to water.
Air
‫׀‬
_________ ‫___________׀‬
Water
‫׀‬
6. In the space below draw a diagram of a light ray
going from water to air.
Water
‫׀‬
_________ ‫___________׀‬
Air
‫׀‬
7. What is the index of refraction n?
The ratio of the speed of light in a vacuum
to the speed of light in a medium.
n = Light speed in Vacuum / Light speed in a medium
8. Light moves through a substance with a speed of
2.2×108 meters per second. What is the index of
refraction for that substance?
n = Light speed in Vacuum /Light speed in a medium
= 3 x 108 / 2.2 x 108
= 1.363636
9. A light ray transitions from air into a substance with
a refractive index of 3.0. If the angle of incidence is
25°, what is the angle of refraction?
This is an application of Snell’s Law which
states that: n1 x sin θinc = n2 sin θrefrac
1 x sin (25) = 3 x sin θ2
Sin-1 (θ2) = 1/3 x sin (25)
Sin-1 θ2 = .42/3 =.14
θ2 = 8°
10.
Draw a diagram for the situation described in
question nine.
‫׀‬
‫׀‬
‫׀‬
11.
What kinds of waves obey the law of reflection?
All waves.
12.
How far does an image in a plane mirror appear
to be behind the surface of the mirror?
The same distance the object is in front of the
plane mirror.
13. Is light refracted when passing between
substances that have the same refractive index?
No. Refer to Snell’s Law.
14. Do different colors of light have the same speed
in a vacuum?
Yes.
15. Do different colors of light have the same speed
in substances?
No, the different colors are slowed down and
bent at different rates when traveling through
substances .
16. Why do different colors of light become
separated when going through a prism?
Colors separate when going through a prism
because in a prism the boundary surfaces are not
parallel but rather at angles to each other causing
light rays to be bent more acutely.