Wave

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Wave: A traveling disturbance that carries energy
through matter and/or space. Waves move through
material…they do not move the material
• Need a vibration as a source
Vibration: source of all waves; particles moving
• Any movement that follows the same path
repeatedly. gives rise to a wave.
Medium: the matter or substance ( s, l, g ), through
which a wave is transmitted. Ex: air-gas; water –
liquids, glass-solids
The parts of a wave:
• CREST: The highest point of a wave.
• Trough: the lowest point of a wave.
What are the 3 major characteristics of waves?
amplitude, wavelength and frequency.
Wavelength:
the distance between 2 consecutive crests or troughs (
crest to crest or trough to trough)
Amplitude: maximum movement from rest. It
shows the energy of the wave!
Height of the wave( rest to crest; rest to trough)
Frequency: the # of complete waves, or cycles,
per second. Higher frequency= more energy
crest and trough = 1 wave
Ex:
Hertz: unit used to measure freq.
Higher the energy, the higher the freq-
Diagram of a Wave- pg. 4
Amplitude
rest
Frequency = crest to trough–
How many are there?
2 types of waves :
1. Transverse: particles move perpendicular to
the direction of the wave propagation
2.Longitudinal:
particles move in the same direction of
the wave propagation
..ex: sound waves
rarefaction
rarefaction
longitudinal
transverse
• Transverse and longitudinal waves can
combine to form surface waves.
• These are how water waves are formed
NOT ALL WAVES NEED A MEDIUM(SOLID, LIQUID
OR GAS)
Mechanical waves: waves that require a
medium
Ex: sound waves, water waves, slinky waves
and rope waves
Electromagnetic waves:
waves that do NOT require a medium- can
move thru space.
Ex: light waves, microwaves, radio waves,
visible light
DO NOW
Ex: light waves
Ex: sound waves
Ex: rope, slinky , water
waves
HAVE 2 CATEGORIES :
TYPE OF WAVE:
Transverse, waves,
transverse,
Needs a medium,
mechanical,
Does not need a medium,
electromagnetic, longitudinal,
Homework
Check :
waves
HAVE 2 CATEGORIES :
mechanical
electromagnetic
NEEDS A:
medium
DOES NOT NEED A:
medium:
TYPE OF WAVE:
longitudinal
Ex: sound waves
transverse
Ex: rope, slinky,
Water waves
transverse
Ex: light waves
://studyjams.scholastic.com/studyjams/jam
s/science/weather-and-climate/waves-andcurrents.htm
• Slinky and rope demo
Light
• Light is an electromagnetic (EM) wave. An
electromagnetic wave is a wave that travels as
vibrating electric and magnetic fields.
• EM waves do not require medium to travel
through.
• EM waves are produced by the vibration of
electrically charged particles.
Study jams on light
• http://studyjams.scholastic.com/studyjams/ja
ms/science/energy-light-sound/light-absorbreflect-refract.htm
Wave bounce back after striking a
.
barrier
during reflection.
Barrier
The normal
Angle of
reflection
Angle of
incidence
A. Of incidence = A. of reflection
Refraction is the bending of a wave when it
passes at an angle from one medium to
another.
Wave
Refraction
• The straw looks
“bent” in the
water
Diffraction
• Waves bend around barriers or through
openings during diffraction.
• Radio waves are most often used for
communication.
• Microwaves
are used for
cooking and
in radar.
• Infrared waves have shorter wavelengths and higher
frequencies than microwaves. The absorption of
infrared waves is felt as an increase in temperature.
• Visible light is the very narrow range of
wavelengths that humans can see. Different
wavelengths are seen as different colors.
• Ultraviolet light is
useful for killing
bacteria and for
producing vitamin D
in the body, but
overexposure can
cause health
problems.
• X rays and gamma rays are EM waves that are often used
in medicine. Overexposure to these EM waves can damage
or kill living cells.
• Highest energy is gamma ray, with shortest wavelength
What is sound?
Sound WaveThe energy produced by a sound, which
emanates outward as a wave in all
directions, and is carried by matter, such as
air.
Sound can also travel through water, glass and
metals.
Anything that vibrates produces sound.
Sound waves require a medium.
Study jams on Sound
Study Jams
Sound
• Waves that require a medium are called
mechanical waves.
• Sound waves are mechanical waves.
• All sounds are created by vibrations and travel
as longitudinal waves.
Frequency
A description of sound known as
high or low is the frequency of
the sound.
Frequency units - Hertz
1 Hz= to 1 wave or cycle
per second.
Fill in on your sound sheet
•
•
•
•
•
Infrasonic: below 20 Hz ( frequency )
Ultrasonic: above 20,000 Hz ( frequency )
Add: Humans hear from 20 – 20 000 Hz (frequency)
Add: SW need a medium
Add: Speed of sound: fastest in a solid, depends on
the medium, and is affected by:
a) temperature, b) density and c) elasticity.
• Echo: reflected SW
• Sonar /ultrasound: reflected SW
• Add: As Amplitude increases, intensity of sound
increases, which makes sounds louder.
Sound waves above
frequencies of 20,000 are
called : Ultrasonic, b/c they
are above range of Human
Hearing.
Ex: dogs, bats, cats, dolphins
Humans hear from 20-20,000 Hz.
Infrasonic:
sound waves below 20 Hzbelow range of human
hearing.
Ex: elephants
Echoes are reflected sound waves.
Some animals use echolocation to find food or
navigate around objects. Sonar and ultrasonography
are types of echolocation. They reflect sound waves !
• Sound
waves
travel
in all
directions
away
from their
source.
Decibel scale – 0- 130 dB ( loudness)
The doppler effect
When there is a motion between the source of
a sound and its receiver,( the person) the
Doppler Effect occurs. THE CHANGE IN
FREQUENCY OF A WAVE, CAUSES THE
DOPPLER EFFECT !
EX: Driving in a car past a police siren or an
ambulance
• The Doppler Effect is the apparent change in frequency of
a sound caused by the motion of either the listener or the
source of the sound.
Speed of sound is determined by the
Temperature, elasticity and density of
the medium through which the sound
travels through.
In general, it travels fastest through solids !
Sound travels slower at a lower temperature,
and faster at a higher temperature.
For elasticity, solids are most elastic, liquids next
elastic and gases the least elastic-therefore the
poorest transmitters of sound
• The speed of sound depends on the medium through
which the sound is travelling. Changes in temperature of
the medium can affect the speed of sound.
• Avg. speed of sound in air at 68 deg. F is about 340 m/s
STOP
Loudness is related to the amount of energy
carried by a wave.
How much energy is carried by the wave in a
certain amount of time is called the INTENSITY
of the wave.
Intensity determines the loudness of sound.
Measured in decibels( dB).
The larger the amplitude, the greater the
intensity, the higher the dB.
Frequencies measured in Hz;
Intensity measured in dB.
PITCH
• The pitch of a sound depends on frequency.
• High-frequency sounds are high-pitched, and lowfrequency sounds are low-pitched.
• Humans can hear sounds with frequencies between
20 Hz and 20,000 Hz.
Highest Pitch
Lowest Pitch
• The intensity of a sound
increases as the amplitude
increases.
• Loudness is affected by
intensity(amplitude), and is
expressed in decibels.
• An oscilloscope can be used to
“see” sounds.
When you speak, your vocal cords vibrate.
When they move inward, the air between them is
pushed together(compressed).
when they move outward, there is less air in that
area, so fewer particles are there (rarefaction).
Let’s do pages 5 and 7 together:
now, page 9 :
Then , get a ruler each, and draw the angle of reflection at
the same angle as the angle of incidence ( incoming light
wave ), but in the opposite side and direction….
Now: we are ready to do a small lab on:
reflection, refraction and diffraction…..
Wave Interference
• The result of two or more waves
overlapping is called interference.
• Amplitude increases during
constructive interference and
decreases during destructive
interference.
What increased?
What decreased?
amplitude
Wave
Diffraction
• Standing waves are waves in which portions
of the wave do not move and other portions
move with a large amplitude.
Sample Calculation
• Calculate the speed of a wave that has a
frequency of 3 waves per second and a
wavelength of .5 m
• 3-Step Answer
– 1. ν = λ x f
– 2. f = 3 waves/sec (Hz)
ν=?
λ = .5 m
– 3. ν = .5 m x 3 waves/sec
ν = 1.5 m/sec
Wave Calculations
• The speed that a wave can travel depends on
the media it travels through
– Ex: The speed of sound through air is 340 m/s, but
through steel it is 5200 m/s.
• The speed that waves are traveling can be
calculated.
• Formula for calculating wave speed: ν = λ x f
– v = speed
– λ = wavelength
– f = frequency
• The sounds you hear are converted into electrical
impulses by your ears and then sent to your
brain for interpretation.
• Exposure to loud sounds can cause hearing
loss and tinnitus.
http://science360.gov/obj/tkn-video/f06b3ba0-6b5f-4e00-a821-6d97dc67ed68
• The speed of light (and all other EM waves) in a
vacuum is 300,000,000 m/s.
• All EM waves travel at the speed of light.
• EM waves differ only by wavelength and
frequency.
• The entire range of EM waves is called the
electromagnetic spectrum.
• http://phet.colorado.edu/en/simulation/bend
inglighthttp://phet.colorado.edu/en/simulation/
bending-light
The main function of the eye is to convert light from the
outside world into electrical nerve impulses
6.
2.
PRODUCES THE
UPSIDE DOWN
IMAGE
AND CONVERTS
TO ELECTRICAL
IMPULSES
1.
MUSCLE THAT
CONTROLS
AMOUNT OF LIGHT
ENTERING EYE.
3.
PROTECTS THE EYE FROM DIRT
AND BACTERIA
PATH FOR ELECTRIC IMPULSES
OPENING THRU
FROM RETINA TO BRAIN
5
WHICH LIGHT
4.
LIGHT ENTERS
ENTERS
AND IS FOCUSED .
The eye
The main function of the eye is to convert light from
the outside world into electrical nerve impulses
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