GCSE Physics - Intro to Waves - Longitudinal and Transverse Waves #61

Summary

This educational video delves into the fundamentals of wave physics, explaining how waves transfer energy without matter. It covers wave labeling, including amplitude, wavelength, crest, and trough, and introduces the concepts of time period and frequency. The video also demonstrates how to calculate wave speed using wavelength and frequency, and distinguishes between transverse and longitudinal waves, providing examples of each. The content is designed to clarify complex wave dynamics in an accessible manner.

Takeaways

• 🌊 Waves are energy transfer phenomena that do not move matter from one place to another.
• 👀 Our brain interprets energy from light and sound waves as meaningful information, allowing us to see images and hear sounds.
• 📊 The displacement distance graph shows how far a wave has traveled and oscillated from its equilibrium point.
• 🔼 Amplitude is the maximum displacement of a wave from its equilibrium position.
• 🌀 Wavelength is the distance of one complete oscillation of a wave, from crest to crest or trough to trough.
• 🕒 Time period is the duration of one complete oscillation, measured when time is on the x-axis of a graph.
• 🔢 Frequency, measured in hertz, is the number of complete oscillations per second and can be calculated using the time period.
• 🚀 Wave speed is calculated by multiplying the wavelength by the frequency, giving the total distance waves travel per second.
• 📏 For a given example, a sound wave with a frequency of 400 Hz and a wavelength of 70 cm (0.7 m) has a speed of 280 m/s.
• ↕️ Transverse waves oscillate perpendicular to the direction of energy transfer, like light and water waves.
• 🔄 Longitudinal waves oscillate parallel to the direction of energy transfer, with regions of compression and rarefaction, such as sound waves.

Q & A

What is the primary function of waves?

Waves transfer energy from one place to another without transferring matter.

Can waves transfer information? If so, how?

Yes, waves can transfer information. For example, light waves from a phone screen or sound waves from speakers can be interpreted by the brain as images or sounds.

What are the key parts of a wave?

The key parts of a wave include the crest (the highest point), trough (the lowest point), wavelength (the distance of one complete oscillation), and amplitude (the maximum displacement from the equilibrium point).

How do displacement-distance and displacement-time graphs differ?

In a displacement-distance graph, the x-axis represents distance, while in a displacement-time graph, the x-axis represents time. The wavelength corresponds to distance in the former, while the time period corresponds to time in the latter.

What is the time period of a wave, and how is it related to frequency?

The time period is the time it takes for one complete oscillation. It is inversely related to frequency, which is the number of oscillations per second. The relationship is given by the formula: Time Period = 1 / Frequency.

How can you calculate the frequency if you know the time period?

Frequency can be calculated using the formula: Frequency = 1 / Time Period.

What equation is used to calculate wave speed, and how does it work?

Wave speed is calculated using the equation: Wave Speed = Wavelength × Frequency. This equation multiplies the length of one wavelength by the number of wavelengths per second, giving the total distance the wave travels per second.

What is the wave speed of a sound wave with a frequency of 400 Hz and a wavelength of 70 cm?

First, convert 70 cm to meters, which is 0.7 meters. Then, multiply by the frequency of 400 Hz. The wave speed is 280 meters per second.

What is the difference between transverse and longitudinal waves?

In transverse waves, the oscillations are perpendicular to the direction of energy transfer (e.g., light waves). In longitudinal waves, the oscillations are parallel to the direction of energy transfer (e.g., sound waves).

Can you provide examples of transverse and longitudinal waves?

Examples of transverse waves include electromagnetic waves (like light and radio waves) and water ripples. Examples of longitudinal waves include sound waves and seismic P-waves.

Outlines

00:00

🌊 Basics of Waves and Energy Transfer

This paragraph introduces the fundamental concepts of waves, emphasizing their role in transferring energy without matter. It explains how waves, such as light and sound, carry energy and can convey meaningful information to our brain, allowing us to perceive images and sounds. The paragraph delves into the terminology of waves, including amplitude, wavelength, crest, and trough, and introduces the concept of displacement and distance graphs to illustrate wave behavior. It also explains the time period and frequency, highlighting their relationship and how they can be calculated using specific equations.

05:01

📏 Understanding Wave Speed and Types

The second paragraph focuses on calculating wave speed and distinguishing between transverse and longitudinal waves. It teaches how to determine wave speed by multiplying wavelength by frequency, using an example of a sound wave to illustrate the calculation. The paragraph also contrasts transverse waves, where oscillations are perpendicular to the direction of energy transfer, with longitudinal waves, where oscillations occur parallel to the energy transfer. Examples of each type of wave are provided, such as electromagnetic waves for transverse and sound waves for longitudinal, concluding with a brief mention of shock waves like seismic P-waves.

Keywords

💡Waves

Waves are disturbances that transfer energy through a medium or space, as described in the video. They are central to the theme as they form the basis for discussing various concepts like energy transfer, wave speed, and types of waves. The script mentions light and sound waves as examples of how waves carry energy without matter.

💡Energy Transfer

Energy transfer refers to the movement of energy from one point to another, which is a fundamental concept in the video. It is exemplified by the script's explanation of how light waves transfer energy from a phone screen to the eye, and sound waves from speakers to the ear.

💡Displacement

Displacement in the context of waves is the distance a point on the wave has moved from its equilibrium position. It is key to understanding wave behavior, as the script describes it in relation to amplitude and wavelength, using a graph to illustrate the concept.

💡Amplitude

Amplitude is the maximum displacement of a wave from its equilibrium position. It is a measure of the wave's energy and is crucial for understanding wave characteristics. The script mentions amplitude when explaining the distance of one complete oscillation.

💡Wavelength

Wavelength is the distance of one complete oscillation of a wave, which could be from peak to trough or from one crest to the next. It is a fundamental property of waves and is used in the script to explain how waves travel and their speed.

💡Crest

The crest is the highest point of a wave, as mentioned in the script when describing the distance of one oscillation. It is an important part of the wave's structure and is used to help understand the concept of wavelength.

💡Trough

The trough is the lowest point of a wave, opposite to the crest. It is used in the script to contrast with the crest and to illustrate the concept of a complete oscillation, which is vital for understanding wavelength.

💡Time Period

The time period is the duration of one complete oscillation of a wave, measured in seconds. It is related to frequency and is used in the script to explain how to calculate frequency and vice versa, providing a way to quantify wave behavior over time.

💡Frequency

Frequency is the number of complete oscillations a wave makes per second, measured in hertz. It is a key concept in the video, as it helps to understand how often a wave oscillates and is used in the script to demonstrate the relationship between time period and wave speed.

💡Wave Speed

Wave speed is the distance a wave travels per second, calculated by multiplying the wavelength by the frequency. It is a central concept in the video, as it quantifies how fast waves propagate and is illustrated with an example of a sound wave in the script.

💡Transverse Waves

Transverse waves are waves where the oscillations are perpendicular to the direction of energy transfer. They are a key type of wave discussed in the video, with examples including light and radio waves, and are contrasted with longitudinal waves.

💡Longitudinal Waves

Longitudinal waves have oscillations that are parallel to the direction of energy transfer, creating regions of compression and rarefaction. They are a type of wave explained in the video, with sound waves and seismic waves as examples, to contrast with transverse waves.

Highlights

Waves transfer energy without transferring matter.

Waves can carry meaningful information that our brain interprets as images or sounds.

A displacement distance graph illustrates the wave's travel and oscillation from the equilibrium point.

Amplitude is the maximum displacement of a wave from its equilibrium position.

Wavelength is the distance of one complete oscillation, from crest to crest or trough to trough.

Crest is the highest point of a wave, while the trough is the lowest.

A displacement time graph shows the wave's oscillation over time.

Time period is the duration of one complete oscillation.

Frequency, measured in hertz, is the number of complete oscillations per second.

The relationship between time period and frequency is reciprocal, calculated as 1/frequency.

Wave speed is calculated by multiplying wavelength by frequency.

An example calculation shows how to find the speed of a sound wave given its frequency and wavelength.

Transverse waves have oscillations perpendicular to the direction of energy transfer.

Examples of transverse waves include light, radio waves, water ripples, and string vibrations.

Longitudinal waves have oscillations parallel to the direction of energy transfer, causing regions of compression and rarefaction.

Sound waves and seismic P-waves are examples of longitudinal waves.

The video concludes with a summary of the key concepts covered.

Transcripts

in today's video we're going to look at

the basics of waves

including how to label the different

parts

how to calculate the wave speed

and the differences between transverse

and longitudinal waves

the first thing to understand about

waves is that they transfer energy from

one place to another but they don't

transfer any matter

so when light waves pass from a phone

screen to your eye

or sound waves pass from the speakers to

your ear

only energy is being transferred

sometimes though we can interpret that

energy as meaningful information

which is why our brain is able to build

up images and tunes from the light and

sounds that it receives

to travel from one place to another

the waves vibrate or oscillate

as we can see in this displacement

distance graph

the distance is how far the wave has

traveled from the starting point

while the displacement is how far from

the equilibrium point the wave has

oscillated

so how far it's gone up or down

the maximum displacement is known as the

amplitude

while the distance of one entire

oscillation is called the wavelength

so that could be from equilibrium

up down and back up

or it could be from the very top of a

wave which we call the crest

down and back up to the next crust

it just has to be one entire oscillation

and the opposite of the crest is called

the trough

now sometimes you might see a

displacement time graph instead

which looks pretty much the same

but because we have time on the x-axis

instead of distance

the length of one complete oscillation

would be the time period instead of the

wavelength

and the time period is just the time it

takes for one complete oscillation

the benefit of knowing the time period

is that we can then use this equation

here to work out frequency

which is measured in hertz

and is a number of complete oscillations

per second

to see how it works imagine that each

oscillation takes 0.5 seconds

or in other words the time period is 0.5

seconds

this means that there must be a total of

two oscillations per second

so the frequency is two

which is what we'd get if we did one

divided by the time period of 0.5

we can also use the equation the other

way around

so time period equals 1 over frequency

so if we were told that the frequency of

a wave was four hertz

which means four oscillations per second

then to find the time period we'd just

do one divided by four

which tells us that each oscillation

must be 0.25 seconds

the next equation to know is that we can

find the speed of the wave

so the wave speed

by multiplying the wavelength by the

frequency

so basically we multiply how long each

wavelength is

by how many there are per second

and that will give us the total distance

they travel per second

to see how this works let's imagine we

had a sound wave that had a frequency of

400 hertz

and a wavelength of 70 centimeters

what is its wave speed

well in this case all we'd have to do is

convert the 70 centimeters to 0.7 meters

because we always want our wavelength in

meters

and then multiply it by the frequency of

400 hertz

which gives us 280 meters per second as

our wave speed

the last thing we need to look at are

the differences between transverse and

longitudinal waves

in transverse waves the oscillations are

perpendicular to the direction of energy

transfer

or the direction in which the wave is

moving

which is why on our drawing the

vibrations are going up and down

whilst the overall wave is traveling

from left to right

most waves we can think of are

transverse

including all electromagnetic waves

like light and radio waves

ripples and waves in water

and the waves of strings like on a

guitar

longitudinal waves on the other hand

have oscillations that are parallel to

the direction of energy transfer

this one's a bit trickier to get your

head around but basically it leads to

some regions that are more spread out

and other regions that are more

compressed

because the waves vibrating back and

forth

in motion it would look as if this area

of compression is moving from the left

to the right within the wave

examples of longitudinal waves include

sound waves

and some types of shock waves like

seismic p waves

anyway that's everything for this video

so hope you found it useful

and i'll see you again soon

you