16-1 Nature of Waves.mp4
Summary
TLDRThis lecture delves into the world of waves, distinguishing between longitudinal and transverse waves. Longitudinal waves, like sound, move in the direction of the disturbance, while transverse waves, such as light, move perpendicularly. Mechanical waves involve the motion of matter, whereas electromagnetic waves are characterized by oscillating electric and magnetic fields. The lecture also explores wave properties like wavelength, amplitude, and period, and how they relate to wave speed and frequency. To engage students, the instructor poses questions about the differences between these wave types and challenges them with a problem involving the calculation of wavelengths for different radio frequencies.
Takeaways
- 🌊 A wave is a disturbance that transfers energy from one place to another, and it can be mechanical or electromagnetic.
- 🔄 Mechanical waves, such as sound waves and water waves, involve the motion of matter and molecules.
- 🌐 Electromagnetic waves, like light and radio waves, carry energy through oscillating electric and magnetic fields.
- ↕️ Transverse waves have disturbances that are perpendicular to the direction of wave travel, like electromagnetic waves and strings.
- 🔄 Longitudinal waves have disturbances that move parallel to the direction of wave travel, such as sound waves.
- 🌀 Water waves are unique as they have both transverse and longitudinal components, causing particles to move in circular paths.
- 🏔 The crest is the highest point of a wave, while the trough is the lowest point, both being part of a wave's cycle.
- 🔗 The wavelength is the distance for one complete cycle of a wave, measured in meters, from crest to crest or trough to trough.
- 🕒 The period is the time it takes for one complete cycle of a wave, and it is inversely related to frequency.
- 🔢 Frequency is the number of cycles per second, and it can be calculated as the reciprocal of the period.
- ⏱️ Wave speed is calculated by multiplying the frequency by the wavelength, with units of meters per second.
Q & A
What is a wave?
-A wave is any disturbance that carries energy from one place to another.
What are the two main types of waves?
-The two main types of waves are longitudinal waves and transverse waves.
How is the disturbance in a transverse wave related to the direction of travel?
-In a transverse wave, the disturbance is perpendicular to the direction of travel.
Give an example of a transverse wave.
-An example of a transverse wave is an electromagnetic wave, such as light or radio waves.
What is the direction of disturbance in a longitudinal wave?
-In a longitudinal wave, the disturbance moves in a direction parallel to the motion of the wave.
What is a common example of a longitudinal wave?
-Sound waves are a common example of longitudinal waves.
Can waves be a combination of transverse and longitudinal?
-Yes, some waves like water waves can have both transverse and longitudinal components.
What is the term for the top part of a wave?
-The top part of a wave is called the crest.
What is the term for the bottom part of a wave?
-The bottom part of a wave is called the trough.
How is wavelength related to the period of a wave?
-The wavelength is the length for one cycle of a wave, and the period is the time for one cycle. They are related through the wave speed, where wave speed equals frequency times wavelength.
What is the relationship between frequency and period?
-Frequency is the inverse of the period, meaning frequency equals one over the period.
How can you calculate the wave speed?
-Wave speed can be calculated by multiplying the frequency by the wavelength.
What are the units for wavelength, frequency, and wave speed?
-Wavelength is measured in meters, frequency in hertz (Hz), and wave speed in meters per second.
How do you find the wavelength of a radio wave given its frequency and the speed of light?
-The wavelength of a radio wave can be found using the formula wavelength = speed of light / frequency.
Outlines
🌊 Introduction to Waves
Chapter 16's first lecture introduces the concept of waves as disturbances that carry energy from one place to another. The lecture covers two main types of waves: longitudinal and transverse. Longitudinal waves, such as sound waves, involve the movement of particles in the same direction as the wave's travel, creating areas of compression and rarefaction. Transverse waves, like those seen in a slinky or electromagnetic waves, have disturbances moving perpendicular to the direction of wave travel. The lecture also discusses the parts of a wave, including the crest, trough, equilibrium point, wavelength, amplitude, and period. Wavelength is the length of one cycle, measured in meters, while the period is the time for one cycle, measured in seconds. Frequency, the number of cycles per second, is the inverse of the period. The lecture sets the stage for understanding the properties and behaviors of different types of waves.
📡 Wave Speed and Radio Frequencies
The second paragraph delves into the concept of wave speed, which is measured in units of length per time (meters per second). It explains that wave speed can be calculated as the wavelength divided by the period or as the product of frequency and wavelength. The paragraph then poses a question about the difference between longitudinal and transverse waves, and between mechanical and electromagnetic waves, reinforcing concepts discussed earlier. It concludes with a practical problem involving the calculation of wavelengths for two radio stations broadcasting at different frequencies: 102.5 FM (102.5 megahertz) and 850 AM (850 kilohertz). The problem requires the application of the formula for wave speed, considering that all radio signals are electromagnetic waves traveling at the speed of light (3 * 10^8 m/s). The solution involves converting the frequency units from megahertz and kilohertz to hertz and then using the speed of light to find the respective wavelengths, emphasizing the importance of scientific notation in the calculations.
Mindmap
Keywords
💡Wave
💡Longitudinal Wave
💡Transverse Wave
💡Mechanical Waves
💡Electromagnetic Waves
💡Wavelength
💡Amplitude
💡Period
💡Frequency
💡Crest
💡Trough
Highlights
Introduction to Chapter 16 focusing on waves, covering sections 16.1 and 16.2.
Definition of a wave as a disturbance that carries energy from one place to another.
Differentiation between mechanical waves, which move a substance, and electromagnetic waves, which carry energy in the form of changing electric and magnetic fields.
Explanation of transverse waves where the disturbance is perpendicular to the direction of travel.
Illustration of electromagnetic waves as a type of transverse wave.
Introduction to longitudinal waves where the disturbance moves in the same direction as the wave's travel.
Sound waves are given as an example of longitudinal waves.
Discussion on waves not being strictly transverse or longitudinal, using water waves as an example of a combination.
Description of periodic waves and their characteristics.
Identification of the crest, trough, and equilibrium point as parts of a wave.
Definition of wavelength as the length for one cycle of a wave.
Definition of period as the time for one cycle of a wave.
Explanation of amplitude as the maximum displacement from equilibrium.
Relation between period and frequency, and their impact on wave speed.
Formula for calculating wave speed as frequency times wavelength.
Question on the difference between longitudinal and transverse waves.
Question on the difference between mechanical and electromagnetic waves.
Problem-solving question involving the calculation of wavelengths for different radio stations based on their frequencies.
Transcripts
welcome to chapter 16's first lecture
this will follow along in chapter 16.1
and
16.2 we'll be looking and introducing
waves different types of waves both
longitudinal and transverse and the
parts of a
wave a wave is any disturbance that
carries energy from place to place um
there are all types of different waves
that we'll look at there are mechanical
waves which move uh a substance they
move a material um it's a disturbance in
materials that's could be like a water
wave a sound wave or all mechanical
waves they involve the motion of
uh of really of just like molecules and
matter in general um then there's
electromagnetic waves which we'll look
at a little bit later on which um they
do still carry energy but in a different
form it's a changing magnetic and
electric field but a wave is just a
disturbance that carries energy from one
place to
another there are two types of waves the
first type of wave that we'll look at is
a transverse wave um in this case the
disturbance is perpendicular to the
direction of travel for the wave so here
we have the wave itself traveling down
the slinky from left to right the
disturbance is moving up and down so the
disturbance is moving back and forth in
a direction that is perpendicular to the
motion of the wave uh electromagnetic
waves or transverse waves we'll also see
these whenever you uh move back and
forth like a string or um something else
there uh so we'll see those often in
class the second type of wave that we
will look at is a longitudinal wave in
this case the disturbance is moves in a
Direction
parallel to the motion of the wave so
here we have and the sprinky the slinky
is as you can see the compressed area
moves um in an area in the same
direction that the waves moves on and
what we'll have is we have an area of
compression and an area of what's called
rare fraction where the stretched where
the spring or whatever the matter is is
stretched out um longitudinal waves only
occur uh they're they're only mechanical
waves so they only occur within matter
um example the most common example is
sound wave sound is a longitudinal
wave on not all waves are necessarily
classified within transverse or
longitudinal um you can't have
combinations of both of them for example
a water wave actually has both a
transverse and longitudinal uh component
to it uh so a water molecule will move
up and down and kind of actually ends up
moving in a circular motion um the
direction of travel for the wave
continues on in this case from left to
right from our drawing but uh they're
not necessarily just a straight UPS
transverse or longitudinal but rather a
combination of both of
them all right parts of a different wave
so periodic waves are any waves that are
repeated over and over again at a
constant rate um there is there are a
couple parts there's one the top part of
a wave the little bubble is called the
crest that little the top Ridge it's
called The Crest where it crosses the
equilibrium point that's called the
equilibrium point excuse me crosses zero
kind of on the for the Y AIS that would
be uh the equilibrium point and when it
gets to the bottom that's the trough TR
r o u g h so the bottom part is the
trough um the wavelength is any is the
length for one cycle similarly the
period is the time for one cycle uh
wavelength is is always measured at
meters um and that can be from a Crest
to a Crest a trough to a trough um but
it's any full complete cycle so one back
and forth motion um amplitude is the
distance from equilibrium to the maximum
uh to the either the crest or the trough
so it's the maximum displacement from
equilibrium once again again period is
the time it takes to complete one cycle
or it's the time it takes for one
wavelength to go by um period is the
inverse of frequency so frequency is how
many cycles per second or frequency is
equal to one over the period um so it's
the rate that a a wave is oscillating
the the rate at which it moves back and
forth so there period and frequency are
related and period once again is the
time it takes to complete one full cycle
or
wavelength speed is in measured in
length per time units of length per time
so that's meters per second uh the
wavelength is is obviously wavelength is
a length and time is usually measured by
the period the time for one cycle so
wavelength over time would give us wave
speed but we can also re rewrite this to
say that uh one over the period is the
same thing as frequency so we could say
that wave speed is the frequency
multiplied by the
wavelength so frequency is units of one
over the seconds wavelength is meters
wave speed frequency times wavelength
meters per
second
all right two easy questions and one
that involves probably a little bit more
thinking so first what is the difference
between longitudinal and transverse
waves second what is the difference
between mechanical and electromagnetic
waves both of those things were touched
on in the video earlier I'm sure they're
in the
textbook Mr Wolf this third question
loves two different radio stations 102.5
FM this is a country radio station it's
broadcast in megahertz that means
million of Hertz which is the unit of
frequency
um so that's
102.5
MHz megahertz um and he loves 850 a.m.
Wei that's where the Red Sox play on
there and that's broadcast in kilohertz
so 850 KZ kerz is a th000 Hertz um given
that all radio signals are
electromagnetic waves that travel at the
speed of light 3 * 10 E8 m/s what are
the respective wavelengths for the two
different radio stations so a little bit
of a plug and solve right there make
sure to pay attention to uh significant
uh excuse me scientific notation there
thank you very much have a good night
and I'll see you in class
tomorrow
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