Transcript Light and Sound - South High School

LIGHT AND SOUND
In this unit:
1)
Properties of light
2)
Reflection
3)
Colours
4)
Refraction
5)
Properties of sound
6)
Hearing
1/5/2015
What are some questions you have about light and color?
What is Light?
What causes it?
ELECTROMAGNETIC WAVES
Electromagnetic waves – light that travels as a
photon through a vacuum or a medium in the form of
radio, micro, visible light, or xrays
27.4 Light and Transparent Materials
Light is energy carried in an electromagnetic wave, generated by vibrating
electric charges.
When light strikes matter, electrons in the matter are forced into vibration.
Frequency – number of waves per second –
measured in hertz
Wavelength – distance from the same part of the
wave
What is the relationship between wavelength and
frequency
5/27
1. How are the electric field and magnetic field in
an electromagnetic wave related to each
other?
2. What causes light?
MEASURING VIBRATIONS
 All waves are caused by vibrations
 Frequency = vibrations / second
 Frequency = cycles / second
 measured in Hertz (Hz)
 Period = time it takes to
Complete a cycle (s)
 1 Hz = 1 cycle / second
Light travels VERY FAST – around
300,000 kilometres per second.
At this speed it can
go around the world 8
times in one second.
SPEED OF LIGHT
27.2 The Speed of Light
Light coming from Io takes longer to reach
Earth at position D than at position A. The
extra distance that the light travels divided by
the extra time it takes gives the speed of
light.
Light year – distance light travels in one year
27.8 Polarized Light and 3-D Viewing
Try these optical illusions.
27.8 Polarized Light and 3-D Viewing
27.8 Polarized Light and 3-D Viewing
1. Recall that it takes one billion nanometers to equal
one meter. Preform the following conversions
6.25*10-7 m = __________ nm
520 nm = _________ m
2. What is the relationship between frequency and
wavelength? C = f *λ
3. How many nanometers are in a meter?
DAILY OBJECTIVES:
-MEASURE THE ANGLE OF INCIDENCE AND THE ANGLE OF REFRACTION TO
DETERMINE THE INDEX OF REFRACTION
- ADVANCED : CALCULATE THE SPEED OF LIGHT IN GLASS
1/6
Warm up
1. What causes the pencil to appear bent when it sits in
water?
2. What happens to the appearance of the small beaker
when emerged in canola oil?
Refraction – the bending of light when it
passes from one medium to the other.
Snell’s law
N1Sinθ1 = N2 Sin θ 2
N = sin i / sin r
N = index of refraction, which is the ratio of the speed of light
in a vacuum to the speed of light in the substance
N = C / velocity in substance
C = speed of light in a vacuum = 3 *10^8
1/7
Recall that the index of refraction is N = speed of light in vacuum/ speed of light in
substance.
What does it mean if the n is less that 1?
1/8 AGENDA : LIGHT REVIEW
FINISH LAB
Percentage error = (experimental – theoretical) / theoretical
Index of refraction = speed of light in a vacuum / in a substance
1. If the book value for the index of refraction is 1.33 and your
measured value is 1.20, what is your percentage error?
2. What are some applications of snells law
3. What happens to the speed of light when in reaches a more
dense medium
WHO MIGHT USE THE PROPERTY OF
REFRACTION?
http://interactagram.com/physics/optics/refraction/
The light rectangle represents the apparent
position of the pencil. Notice that the end
(X) looks like it is at (Y), a position that is
considerably shallower than (X).
As the light goes from the water to the air
does its velocity increase or decrease?
CAN YOU THINK OF SOME TECHNICAL
APPLICATIONS FOR SNELL’S LAW?
WHAT CAUSES A MIRAGE
As light approaches the
hotter air near the ground
it bends away from the
normal
6/2
Why are diamonds so shinny?
Why might it be useful to know a materials index of refraction?
What are some applications of Snell’s law?
Finish CER
SNELL’S LAW CONCLUSION
Claim – what did you find in your experiment
Evidence – Use your picture and calculations for this. How close to 1.33 where your
measurements, you can use percentage error calculations in these.
[1.33– measured value] / 1.33
Reasoning – How does your experiment show refraction. What are some possible
errors. Use vocabulary like angle of incidence, angle of reflection and normal to
describe what is happening
http://www.youtube.com/watch?v=blnL6z3teUE - computer simulation of a diamond
http://www.youtube.com/watch?v=dWwQqI2BkVc - Snell’s laws song
Singin’ n1 sine theta-sub1 hey, hey hey
Equals n2 sine theta –sine sub 2 hip hip hooray
29.8 Refraction of Light
a.
b.
c.
The apparent depth of the glass block is less than the real depth.
The fish appears to be nearer than it actually is.
The full glass mug appears to hold more root beer than it actually does.
These effects are due to the refraction of light whenever it crosses a boundary
between air and another transparent medium.
27.2 The Speed of Light
The speed of light in a vacuum is a universal constant.
Light is so fast that if a beam of light could travel around Earth, it would make 7.5 trips
in one second.
Light takes 8 minutes to travel from the sun to Earth and 4 years from the next nearest
star, Alpha Centauri.
The distance light travels in one year is called a light-year.
27.7 Polarization
If the rope is shaken up and down, a vertically polarized wave is produced.
The waves traveling along the rope are confined to a vertical plane.
If the rope is shaken from side to side, a horizontally polarized wave is
produced.
27.8 Polarized Light and 3-D Viewing
A 3-D slide show uses polarizing filters. The left eye sees only polarized light from
the left projector; the right eye sees only polarized light from the right projector.
27.7 Polarization
A vibrating electron emits a polarized electromagnetic wave.
A vertically vibrating electron emits vertically polarized light.
A horizontally vibrating electron emits horizontally polarized light.
27.7 Polarization
A rope analogy illustrates the effect of crossed sheets of polarizing material.
27.7 Polarization
a.
b.
Light is transmitted when the axes of the polarizing filters are aligned.
Light is absorbed when they are at right angles to each other.
POLARIZATION
5/16
What are some differences between light and
sound?
What is one thing you learned from your
classmates yesterday?
5/17
True or false black is a combination of all the colors
What do you see below?
Why is candle light more romantic?
1/9
1. The color green has a wavelength of
520 nanometers, what is its wavelength
in meters? (hint I meter =
1,000,000,000 or one billion
nanometers)
2. Write this number in scientific notation.
1/10
Draw a picture and write a formula for each of the
problems
1. The mass of one hydrogen atom is 1.67 * 10-27 kg. A
cylinder contains 3 * 1023 atoms. What is the mass of
the atoms?
2. The average distance from the Earth to the sun is 1.5
*1011 m. The speed of light is 3*108 m/s. How long
does it take for light to travel from the sun to the earth?
Exponent rules
When multiplying scientific notation add
exponents
When dividing subtract exponents
Hint for Physics fix 30 s= d/t what are the other two?
1/15
1. List the types of waves on the electromagnetic spectrum
from lowest frequency to highest frequency.
2. Radio waves travel at the speed of light at 300,000 km
per second. The Frequency of the radio wave is 150
mega hertz. What is the wavelength? ( hint mega=
1,000,000 kilo= 1,000)
wave speed = frequency * wavelength)
1. Test today
1/15
1. List the types of waves on the electromagnetic spectrum
from lowest frequency to highest frequency.
2. Radio waves travel at the speed of light at 300,000 km
per second. The Frequency of the radio wave is 150
mega hertz. What is the wavelength? ( hint mega=
1,000,000 kilo= 1,000)
3. wave speed = frequency * wavelength)
4. Test tomorrow
C = frequency * wavelength
wave speed = wavelength x frequency
v= λxf
C= F * λ
C = is speed of light 3* 10^8
F = frequency = vibrations per second measured in hertz
Λ ( greek letter lambda) Wavelength = measured in
meters
Light is measured in namometers.
What determines the color something is?
Why does yellow feel cool in the summer?
Yellow is the light from the sun that is reflected back, what is not
reflected is absorbed so this is why black feels the warmest in
the summer.
Ozone – blocks harmful UV rays
Why the sky is blue
Blue light is absorbed and then scattered
The colors of the objects
depend on the color of the light
that illuminates them.
Color is in the eye of the beholder
and is provoked by the
frequencies of light emitted or
reflected by things. We see red in
a rose when light of certain
frequencies reaches our eyes.
Many organisms, including
people with defective color
vision, see no red in a rose.
COLOR
The colors of the objects depend on the color of the light
that illuminates them.
Color depends on the wavelength that is reflected back.
28.1 The Color Spectrum
Isaac Newton was the first to make a systematic study
of color.
Passing sunlight through a glass prism, Newton
showed that sunlight is composed of a mixture of all
the colors of the rainbow.
Newton called this spread of colors a spectrum, and
noted that the colors were formed in the order red,
orange, yellow, green, blue, and violet.
What is the jist of this passage?
28.1 The Color Spectrum
When sunlight passes through a prism, it separates into a spectrum of all the colors
of the rainbow.
1/16
1. Compare gamma rays to radio waves.
a. Which one has a greater frequency?
b. Which one has a greater wavelength?
c. Where is each one found?
2. What is the wavelength of a radio wave that has a
frequency of 10 Hz?
Due today – snell’s law lab
Notebook check 1/8 – 1/16
28.2 Color by Reflection
Light Sources
The color of an object depends on the kind of light
used.
• A candle flame is deficient in higher frequencies;
it emits a yellowish light. Things look yellowish in
candlelight.
• An incandescent lamp emits light of all the
visible frequencies, but is richer toward the lower
frequencies, enhancing the reds.
• A fluorescent lamp is richer in the higher
frequencies, so blues are enhanced when
illuminated with fluorescent lamps.
• Do you think you look better in certain light?
• Why is candle light more romantic?
28.2 Color by Reflection
a.
b.
This square reflects all the colors illuminating it. In sunlight, it is white.
When illuminated with blue light, it is blue.
This square absorbs all the colors illuminating it. In sunlight it is warmer
than the white square.
28.4 Sunlight
The radiation curve of sunlight is a graph of brightness versus frequency.
Sunlight is brightest in the yellow-green region.
Mini lab:
Which folder will be brighter under red light, blue or
red?
Which folder will be brighter under blue light, blue or
red?
Expain:
28.5 Mixing Colored Light
The low-frequency, middle-frequency, and high-frequency parts of white light appear
red, green, and blue.
To the human eye, red + green = yellow;
red + blue = magenta; green + blue = cyan.
28.6 Complementary Colors
Six blocks and their shadows appear as different colors depending on the color of light
that illuminates them.
28.2 Color by Reflection
Petals of most yellow flowers, such as daffodils, reflect red and green as well as yellow.
Yellow daffodils reflect light of a broad band of frequencies.
The reflected colors of most objects are not pure single-frequency colors, but a spread
of frequencies.
So something yellow, for example, may simply be a mixture of colors without blue and
violet—or it can be red and
green together.
Main idea : The color you see is a combination of frequencys that are reflected back
into your eye.
WHY IS THE SKY BLUE
Why is the sky blue?
Sunlight reaches Earth's atmosphere and is scattered in all directions by all the gases
and particles in the air. Blue light is scattered in all directions by the tiny
molecules of air in Earth's atmosphere. Blue is scattered more than other colors
because it travels as shorter, smaller waves. This is why we see a blue sky most
of the time.
WHAT MAKES A RED SUNSET?
28.8 Why the Sky Is Blue
The sky is blue because its component particles scatter
high-frequency light.
28.8 Why the Sky Is Blue or black
The higher that one goes into the atmosphere, the fewer molecules there are
in the air to scatter light.
The sky appears darker.
When there are no molecules, as on the moon, for example, the “sky” is
black.
LAW OF REFLECTION
THE ANGLE OF INCIDENCE = THE ANGLE OF
REFLECTION
Refraction – the bending of light due to a change in
light speed
Coming up
next on
Monday
snell’s law
Which topic did you choose?
What is the main idea behind your topic?
Today –
-present your findings to classmate
-Fill out exit slip
5/15
Are you ready to present?
What are some characteristics of a strong presentation?
Exit slip – write a paragraph reflection on how you did.
What was the main idea. What extra information did
you have. Rate yourself 1-5. What did you do well,
what could use work?
5/16
1. What is one thing you learned from your classmates
regarding light?
Light travels much faster than sound. For example:
1) Thunder and lightning
start at the same time,
but we will see the
lightning first.
2) When a starting pistol
is fired we see the
smoke first and then
hear the bang.
PROPERTIES OF LIGHT SUMMARY
1)
Light travels in straight lines
2)
Light travels much faster than sound
3)
We see things because they reflect light into our eyes
4)
Shadows are formed when light is blocked by an object
We see things because they
reflect light into our eyes:
Homework
SEEING COLOUR
The colour an object appears depends on the
colours of light it reflects.
For example, a red book only reflects red light:
White
light
Only red light
is reflected
ADDING COLOURS
White light can be split up to make separate
colours. These colours can be added together
again.
The primary colours of light are red, blue and
green:
Adding
blue and red
Adding blue and
makes magenta
green makes cyan
(purple)
(light blue)
Adding red
and green
makes yellow
Adding all
three makes
white again
A pair of purple trousers would reflect purple light
(and red and blue, as purple is made up of red and blue):
Purple light
A white hat would reflect all seven colours:
White
light
In different colours of light this kit would look
different:
Red
light
Shirt looks red
Shorts look black
Shirt looks black
Blue
light
Shorts look blue
PART 2 - REFLECTION
Reflection from a mirror:
Normal
Reflected ray
Incident ray
Angle of
incidence
Angle of
reflection
Mirror
The Law of Reflection
Angle of incidence = Angle of reflection
In other words, light gets reflected from a
surface at ____ _____ angle it hits it.
The
same !!!
CLEAR VS. DIFFUSE REFLECTION
Smooth, shiny surfaces have a clear
reflection:
Rough, dull surfaces have
a diffuse reflection.
Diffuse reflection is when
light is scattered in
different directions
5/22
1. The color green has a wavelength of
520 nanometers, what is its wavelength
in meters? (hint I meter =
1,000,000,000 or one billion
nanometers)
2. Write this number in scientific notation.
6TH HOUR ASSIGNED SEATS
1. Recall that it takes one billion nanometers to equal one meter.
Preform the following conversions
6.25*10-7 m = __________ nm
520 nm = _________ m
Why is the sky blue?
Agenda
Physics fix 30
29.10 Dispersion in a Prism
Dispersion through a prism occurs because different frequencies of light travel at
different speeds.
COLOUR
White light is not a single colour; it is made up of a mixture of the seven
colours of the rainbow.
We can demonstrate this by
splitting white light with a
prism:
This is how rainbows are
formed: sunlight is “split
up” by raindrops.
THE COLORS OF THE RAINBOW:
Red
Orange
Yellow
Green
Blue
Indigo
Violet
29.11 The Rainbow
Dispersion of sunlight by a water drop produces a rainbow.
29.11 The Rainbow
Light from droplets inside the rainbow form a bright disk with the colored rainbow at its
edge. The sky appears darker outside the rainbow because there is no light exiting
raindrops in the way that produces the main rainbow.
29.11 The Rainbow
think!
If light traveled at the same speed in raindrops as it does in air,
would we still have rainbows?
29.12 Total Internal Reflection
a-d. Light emitted in the water at angles below the critical angle is partly refracted and
partly reflected at the surface.
e. At the critical angle, the emerging beam skims the surface.
f. Past the critical angle, there is total internal reflection.
29.12 Total Internal Reflection
Optical Fibers
Optical fibers, sometimes called light pipes, are transparent fibers that pipe
light from one place to another.
They do this by a series of total internal reflections.
Optical fibers are useful for getting light to inaccessible places.
Mechanics and machinists use them to look at the interiors of engines, and
physicians use them to look inside a patient’s body.
29.11 The Rainbow
think!
If light traveled at the same speed in raindrops as it does in air,
would we still have rainbows?
Answer:
No. If there is no change in speed, there is no refraction. If there is
no refraction, there is no dispersion of light and hence, no
rainbow!
Assessment Questions
1.
Scientists now agree that light is composed of
a. only electromagnetic waves.
b. only photons.
c. electromagnetic waves and particles called photons.
d. an unknown source.
Assessment Questions
1.
Scientists now agree that light is composed of
a. only electromagnetic waves.
b. only photons.
c. electromagnetic waves and particles called photons.
d. an unknown source.
Answer: C
Assessment Questions
3.
All of the following are part of the electromagnetic spectrum EXCEPT
a. light.
b. sound.
c. radio waves.
d. X-rays.
Assessment Questions
3.
All of the following are part of the electromagnetic spectrum EXCEPT
a. light.
b. sound.
c. radio waves.
d. X-rays.
Answer: B
Assessment Questions
5.
Light that is not transmitted by opaque materials is
a. converted to internal energy in the material.
b. mainly reflected.
c. mainly refracted.
d. transmitted at a lower frequency.
Assessment Questions
5.
Light that is not transmitted by opaque materials is
a. converted to internal energy in the material.
b. mainly reflected.
c. mainly refracted.
d. transmitted at a lower frequency.
Answer: A
Assessment Questions
8.
The best way to view something in 3-D is to
a. have keen eyesight.
b. use two eyes.
c. use only one eye.
d. be slightly cross-eyed.
Assessment Questions
8.
The best way to view something in 3-D is to
a. have keen eyesight.
b. use two eyes.
c. use only one eye.
d. be slightly cross-eyed.
Answer: B
Assessment Questions
2.
To say that rose petals are red is to say that they
a. absorb red.
b. reflect red.
c. emit red.
d. transmit red.
Assessment Questions
2.
To say that rose petals are red is to say that they
a. absorb red.
b. reflect red.
c. emit red.
d. transmit red.
Answer: B
Assessment Questions
8.
The blueness of the daytime sky is due mostly to light
a. absorption.
b. transmission.
c. reflection.
d. scattering.
Assessment Questions
8.
The blueness of the daytime sky is due mostly to light
a. absorption.
b. transmission.
c. reflection.
d. scattering.
Answer: D
Assessment Questions
6.
Refraction occurs when a wave crosses a boundary and changes
a. speed and direction.
b. intensity.
c. frequency.
d. amplitude.
Assessment Questions
6.
Refraction occurs when a wave crosses a boundary and changes
a. speed and direction.
b. intensity.
c. frequency.
d. amplitude.
Answer: A
1. How does your TV screen make every color?
2. What happens to light when it goes from a more dense medium into a
less dense medium?
a. Speeds up and goes towards normal
b. Speeds up and goes away from normal
c. Slows down up and goes towards normal
d. Slows down up and goes away from normal
3. Are you ready for the quiz?
Notebook check # of dates from 5/13