16-1 Nature of Waves.mp4

Summary

This 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

00:00

🌊 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.

05:02

📡 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.

Keywords

💡Wave

A wave is defined as any disturbance that carries energy from one place to another. In the context of the video, waves are the central theme, with the lecture focusing on different types of waves, their properties, and behaviors. Waves can be mechanical, involving the motion of molecules and matter, or electromagnetic, involving changing electric and magnetic fields.

💡Longitudinal Wave

A longitudinal wave is a type of wave where the disturbance moves in the same direction as the wave's travel. The video uses the example of a slinky to illustrate this, where the compression and rarefaction (areas of compression and stretching) move along the slinky in the direction of the wave's propagation. Sound waves are given as a common example of longitudinal waves.

💡Transverse Wave

Transverse waves are characterized by disturbances that are perpendicular to the direction of wave travel. The video describes how, in a transverse wave, the oscillations occur up and down while the wave itself moves from left to right, as demonstrated with a slinky. Electromagnetic waves and waves on a string are examples of transverse waves.

💡Mechanical Waves

Mechanical waves are disturbances that move through a material medium, such as water or air. The video explains that these waves involve the motion of molecules and matter, and examples include water waves and sound waves. Mechanical waves require a physical medium to propagate.

💡Electromagnetic Waves

Electromagnetic waves are a type of wave that carries energy through a changing electric and magnetic field. Unlike mechanical waves, they do not require a physical medium to travel and can propagate through a vacuum. The video mentions that these waves will be discussed later, indicating their importance in the broader study of waves.

💡Wavelength

Wavelength is the physical length of one complete wave cycle, measured from one point of corresponding phase to the next. The video explains that wavelength can be measured from crest to crest or trough to trough, and it is a fundamental property of a wave, used to calculate wave speed.

💡Amplitude

Amplitude refers to the maximum displacement from the equilibrium position of a wave. It is a measure of the wave's energy and is described in the video as the distance from the equilibrium point to either the crest or the trough of the wave.

💡Period

The period of a wave is the time it takes for one complete cycle to occur. The video clarifies that period and wavelength are related, with the period being the time for one wavelength to pass a given point. It is inversely related to frequency.

💡Frequency

Frequency is the number of wave cycles that pass a given point per unit of time, typically measured in Hertz (Hz). The video explains that frequency is the inverse of the period, meaning the higher the frequency, the more cycles occur in a given time frame.

💡Crest

The crest of a wave is the highest point of the waveform, representing the peak of the wave's oscillation. The video uses the crest to illustrate the concept of amplitude and the measurement of wavelength.

💡Trough

A trough is the lowest point of a wave cycle, opposite to the crest. The video mentions the trough in the context of defining amplitude and the characteristics of wave cycles.

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