Ex In the ocean waves travel across but the water only oscillates up and down returning to their original position Pulse a single wave from a disturbance Ex Throwing a rock in water a pulse travels in all directions from the point of contact ID: 783711
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Slide1
What is a Wave?
Wave- movement of a disturbance (energy) without a net movement of matter
Ex. In the ocean, waves travel across but the water only oscillates up and down returning to their original position
Pulse - a single wave from a disturbance
Ex. Throwing a rock in water (a pulse travels in all directions from the point of contact)
Slide2Types of Waves
Mechanical Waves- waves that require a medium to travel through
in the ocean, water is the medium; for sound, air is usually the medium.
Electromagnetic Waves- waves that do not require a medium to travel through
Ex. Light, radio waves, x-rays, microwaves
Slide3Shapes of waves
Transverse wave- the particles of the medium move perpendicular to the direction of wave movement (wave propagation)
Ex. Waves in water, doing the wave at a football game
Longitudinal Wave- particles of the medium oscillate parallel to the direction of wave propagation
Ex. Sound wave
Slide4Shapes
Transverse Wave
Longitudinal
Wave
The wave moves
The particles move
compression
rarefaction
Wavelength
Slide5Wave Equation
Slide6Wave Equation
v = d/t
Wavelength (
)- length of one
wave (m)
Period (T)- time it takes for one complete wave to travel past a given
point (s)
Frequency (f) number of waves to pass by in a second (Hz)v = / TT = 1/f v = f
Slide7Problems
92.3 The Fan
broadcasts its radio station at 92.3 MHz (Mega means 10
6
). Radio waves are electromagnetic and travel at the speed of light (3.00 x 10
8
m/s). What is the wavelength of the signal sent out? What is the period of the waves sent out?
v =
f 3.00x108 = ()92.3x106 Hz ; = 3.25 m
T = 1/fT = (92.3x106 Hz)-1 = 1.08 x10-8
sec
Slide8Echolocation
Bats
and dolphins use
a sonar style adaptation to “see” the
world called echolocation.
What
that means is they emit sound waves and have receptors to check for their
reflections, echoes.
If the wavelength of their sounds waves is larger than their target, they likely will miss it. Therefore, they must keep the wavelength shorter than their target.
Slide9SONAR
SO
und
NA
vigation
and
R
angingA SONAR machines were developed in the early 1900’s that emitted a sound into the water to locate objects in the water. This became very important in WWII to determine the location of submarines.
Slide10SONAR
If
the speed of sound in air is 346 m/s at 25
C, and bats main target would be an insect no bigger than
.60
inches long, at what frequency must they emit their sound waves?
(0.60
in = 0.015 m)sound navigation and ranging
Slide11Answer
v
= f
346 m/s = .
015
m (f)
f = 23000 Hz to hit a bug no bigger than .60 inches it can be greater than or equal to 23000 Hz This type of sound is called ultrasound, and can’t be heard by humans.
Slide12One More
A spring was placed in a pool, the spring has a spring constant, k of 490 N/m.
When the spring was set into motion with a mass of
1250
kg, it created
a
wave action in the pool. The period of oscillation will be equal to the period of the waves created. If you noted that the waves were 5.0 m apart, and it was 102
m
from the spring to “shore”, how long would it take for a wave to go from creation to the shore?