Waves REVISION PODCAST (Edexcel IGCSE physics topic 3)

Waves REVISION PODCAST (Edexcel IGCSE physics topic 3)

Hello! This is a revision podcast for Excel I G C S E and this is on topic
3 waves. There are two kinds of waves: transverse and longitudinal waves. Longitudinal waves vibrate back and forth in the direction in which
the wave travels this could be a slinky spring here are areas where the spring has been
compressed. The spring will pass on that vibration to the adjacent particle. That particle will move forwards and
then move back into position. The wave moves across to the right but
the particles themselves move forwards and backwards. Areas where the waves are close together are compressions. And areas where they are spread apart are called rarefactions. Transverse
waves vibrate up and down across the direction
of travel in this example the wave is moving to
the right but the water (if it was a
water wave) or the particles would move up and then back down again.
The wavelength is the distance from one peak to the next and the amplitude from the
center of a wave to the top. Both of these kinds of wave
transfer energy although neither of them transfer any matter. The time period is the time it takes to make one
complete oscillation so that will be measured in seconds
which are the standard units for time. the frequency is the number of vibrations made in a second and that has standard units hertz (Hz) which means the number per second. In this graph you can see that as the time
period reduces the frequency increases. In fact the
relationship between frequency and time period is reciprocal frequency is one over the time period.
You are given this equation on the Excel paper. Here is an example using that equation: if a jigsaw blade vibrates up and down at a frequency of 80 hertz, how long
does it take to make one complete vibration? That’s the time period. You
rearrange this formula to make T the subject that will be T equals 1 over f. Substitute the data: 80 Hertz. 1 over 80 is 0.0125 seconds that’s the time period for the jigsaw
blade. The wave equation relates the wave speed to the wave’s
frequency and its wavelength. The letter lambda is a Greek L and that represents the
wave length as the frequency of a wave decreases the wavelength increases for example if the waves at the shore for beach arrive
at a frequency of 0.4 hertz and are eight meters apart, calculate the
wave speed. so you’d use this equation in this form wave speed would be the frequency times by the wavelength gives 3.2 meters
per second note the the units here are standard so
the output units are also standard units for speed – or
meters per second Any wave involving electromagnetic waves would travel at
the speed of light so if a question asked you: Radio one is
broadcasting a radio wave 97.9 megahertz what would be its wavelength? You’d rearrange this
equation to make a lambda the subject. So if you
use a triangle cover up this term and that leaves v divided by f. Lambda is speed over frequency so 3 x 10^8 over 97.9 x 10^6 that’s 97.9 million gives 3.06 meters When waves pass through a gap they
spread out slightly this process is called diffraction diffraction is greatest when the
wavelength of the wave that’s the distance from one peak to the
next is about the same size as the width of the gap and destroying the show’s about maximum
diffraction was the wavelength here is about the
same size as the gap when you draw these diagrams note that
the wavelength remains constant throughout distance here is about the
same as the distance here diffraction happens when there’s only
one edge in this case the gap is considered very
large and so the diffraction is greatest when the wavelength is very large I E a very long distance gap so a very
long way will def racked the most always to fract including lights but we
don’t observe like defecting very much because its wavelength is so small you’d need a very small gap to see its
diffraction you need to know about electromagnetic
waves which are oscillations electric and magnetic fields that may sound confusing but the part of
a family of well-known waves three from long wave radio waves to very
short wave gamma rays all electromagnetic waves carry energy but only the shortest wavelength ones
are ionizing gamma rays a very ionizing and
ultraviolet least ionizing all electromagnetic waves travel at the
same speed that’s the speed of light here’s a new moniker might help you
learn the spectrum in terms of frequency amp it starts with
gamma rays which are the lead shortest wavelength
and goes to radio waves which are the longest wavelength I can’t
claim credit for this demonic it was invented by one of my students generally the higher the frequency the
more dangerous the electromagnetic wave gamma X rays and ultraviolet are all
ionizing it’s not about some uses and some
dangers electromagnetic waves here some statements taken from the
syllabus ready way to use for broadcasting Mike Rice for cooking infrared for
heating visible light ultraviolet X-rays and gamma rays all have uses and hear
some dangers microwaves will he to internal body
tissue they don’t ionized a infrared can cause
skin burns it’s also not ionizing ultraviolet does damage to the skin surface cells
and blind and can cause blindness and gamma rays can cause cancer and can
mutate cells mirrors will reflect light according to
the law of reflection that is that the angle of
incidence is equal to the angle of reflection you measure angles to the normal line a
normal line is drawn at 90 degrees to the surface of the mirror you need to build to
construct a diagram to show the location of on image so here is an object that we’re looking
at and the image is formed the same
distance away inside the mirror so after all on the image location equally distant and
level with the object here if an observer looks at this object they will see the image inside the
mirror this ray diagram shows you how it forms
have the image forms here to start off with your ruler at the
position of the image and you draw or brave that goes to the
mirror and continues to the eye that ray would’ve come from the in the
object over here and it reflects at the mirror surface I’ve repeated that process for a second
ray of light and you can see that diverging spreading
out if you put your pencil at the object
position and join a lineup with where the ray
hits the mirror you will get an accurate reflection these rays reflect of the mirror go to
the RI these rays aren’t real they’re called
Virtual Race and they should be door drawn dotted now the diagrams complete we haven’t
image that’s inside the mirror the same
distance away but laterally inverted that is swapped
left to right and that’s virtual the image can’t be
formed on the screen from these rays nope really travel there
is no light here virtual raise to show where the
image appears you can see reflections mirrored surfaces and also obviously at
waters edge is refraction is what happens when a wave
changes speed here waves kept to a boundary and they
travel slower in this medium one side of the way
travels faster than the other side of the way and so it overtakes and they travel in a
different direction once they go into the other medium note that the wavelength is also shorter
in the slower medium this happens to light when it travels
into glass the angle of incidence is greater than
the angle of refraction as the light bends towards the normal a normal line here is at 90 degrees to
the surface as it was for a merit roaring an analogy to explain it would be a car
driving from tarmac into mud as the car drives towards the mud eventually one wheel gets to the mud
before the other we’ll this wheel will travel slower and this
will foster so the car will change direction one
side will be traveling faster and it will turn here the car is now change direction and once it’s entered the mud it will
continue going to straight-line when it leaves the mud on the other side
the opposite will happen and this we’ll we’ll get traction first
and the car will move back to its original path the mathematics of
refraction are that n the refracted index of the
material is equal to Sinai over synar and that
could be put into a triangle to help you manipulate the formula the
opposite of the sine function is signed to the -1 he normally press
SHIFT and then sign on your calculator you’ll need that in the examples so much
in light enters glass at an angle of 45 degrees
to the normal and refracts 29 of 30 degrees calculate
the refracted index formula here is used in this form Sinai over synar which comes out to be
1.41 that’s the refracted index at the glass
and it doesn’t have units it’s a ratio in this example we want to know what angle light will
refract T when it enters diamond at an angle diamonds refracted indexes
2.4 because we want to know what angle it
refracts to you we need to cap Hill 8 are of formula rearranges to give us sign a bar sign a
bar Sinai over N which comes out to be not point 319 that isn’t the angle of refraction bio to find that
we need to use the inverse sine function are is the inverse sin of the art so we
just got which gives 18.62 grease worth checking
when you’ve got an answer but a look sensible compared to the
original angle of incidence let’s consider what happens to light
when it tries to leave glass or more optically dense material
if it travels at a fairly shallow angle it will refract and leave the class it
bans away from the normal of course if you increase the angle of incidence
at the surface eventually the lights will graze along
the glass surface edge it does that at an angle called the
critical angle so acts the critical angle light bends as far as it possibly can along
the surface of the glass beyond to the critical angle litres got nowhere left to refract and
so it reflects inside to block all the light energy reflects none comes out
and so this is called total internal reflection the
relationship between two critical Anglesey and to refract if index have the glass
is this sign see equals 1 over N and you could
put that into a triangle to help you manipulate
it again to calculate the critical angle for perspex if you know it’s reflective indexes 1.4
again you start by calculating sign of the critical
angle which is 1 I’ve Iran with that number we then need to use the
inverse sine function again to calculate the critical angle which
comes out to be close to 45 or 46 degrees a prism can disperse light into its constituent colors here white
lights refracts when enters and refract again
as it leaves the prism but the refractive index of blue lights is slightly more the refracted index for
red light so it bends slightly more and the white
light is split into its constituent colors when light hits this prism its arrives
at the surface at the normal line and so it doesn’t
refract and hits this surface at an angle a 45
degrees to the normal which is above the
critical angle and so it reflects the same process
happens again here and we’ve used these prisons to create a
periscope SLR cameras use presumes to reflects
light down through the lens of a camera so
that you see a picture of what you’re about to take like can be transmitted along optic
fibers as a digital signal the light flashes on and off quickly to
represent am code of ones and zeros which is a binary code light hits the edge at an angle greater than
the critical angle between the two materials and so always totally internally
reflects analog signals take any shape or size
but digital signals are either on or of when you transmit signals along any in any medium noise
can distort them let’s have a look at the distorted
signals so he’s the signals with some noise
added to them you can see the analog signal has lost
some of its original integrity we could clear this up but it would be
less like the original shape whereas a digital signal you can still interpreters ones and zeros you still
know if the voltage is high or low or in this case if the
light intensity is bright or dim so digital signals are less prone to noise by interference
and the original can be cleared up sound waves along tattooed no vibrations
a family kills the air from a loudspeaker moves back
and forwards and Knox into the molecules of its
neighbors creating a compression wave like other way a sound can be reflected
at san ako it can be refracted and it can be
diffracted you need to know experiment to measure
the speed of sound to do so you need some people a large
distance away from a loud sound you use a gun you by the guy and you’d watch for the smoke the people
would start the stopwatch when they saw the smoke and stop it when they hear the bank they
do see question speed equals distance over time to calculate that speed but the sound to
take and travel there are other methods for working at
the speed of sound other methods may be more accurate than
this method but this method works if you connect a microphone to an
oscilloscope you can create a trace that represents the sound the trace would be voltage produced by
the microphone against time but the voltage represents
the position or movement of the microphone had the time period can be measured from the
time taken to from one wave to the next and you could use the
frequency former remember that was given on the pegs am
paper to calculate the frequency of the wave if you knew its time period higher
sounds have higher frequencies when object vibrates the Soundwave a
crate on this telescope will look different depending on the
sound is producing the app to cheat and the wavelength
represents the loudness on the pitch can you work
out which one of these waves his loudest and which one is highest the higher the pitch the shorter the
period over wave so this one represents the highest pitch
sound because it has the highest frequency and
therefore shortest time period the Bourne object vibrates
the greater the empty will be so be represents the quietest wave and the shape of a wave indicates what
was vibrating so love these were the same instrument
and the was slightly different instruments it
vibrates in a slightly different way humans here sounds from about 20 to
about 20,000 hurts although as you get older this high-end
tends to drop off

57 thoughts on “Waves REVISION PODCAST (Edexcel IGCSE physics topic 3)

  1. These videos are great 🙂 But what about things like the rules for total internal reflection and how optic fibres work along with their uses?

  2. 5:37 you say gamma has a high ionizing power, doesn't it have a high penetrating power and a low ionizing power? please correct me if im wrong

  3. Great video!!!Well, don't we need to know the experiment to measure the speed of sound using resonance?

  4. There is nothing on the specification about an experiment to measure the speed of sound using resonance. In fact, resonance is not mentioned either, so it's unlikely that this will be examined. But Edexcel have surprised us in the past!

  5. Thank you very much. Just to make sure, do this playlist plus the playlist consisting of the extra parts related to CIE IGCSE cover the entire CIE  syllabus? Also it'd be great if you post any notes you pass out to your students. Thanks again!

  6. thanks a lot for this video but what about the experiment how to measure speed in air using a resonance tube 😅

  7. I am deeply upset that my impeccable revision notes have been ruined, by what are in general useful videos. I am talking in particular about YOU drawing a straight virtual image line, and then a dotted line (8:01), causing me to ruin my needless to say, spectacular notes. EXTREMELY ANNOYING! For a man of your academic pride, I expected better, than this low grade apathetic approach.

  8. the mnemonic for EM spectrum waves by the edexcel igcse revision guide is
    "R"un "M"iles "I"n "V"ery "U"npleasant e"X"treme "G"ames

  9. halo sir thank you for your well explained videos i am not really good in physics and I think your videos will help me 🙂

  10. Thank you sir. i have my mock exam next week and i hardly understood anything about waves in class these videos are so helpfull. p.s i hope you dont mind but i downloaded the video😊

  11. Thank you so much for this! Waves has been my worst topic for a while now in Physics but now I think I finally understand it.

  12. Sorry if this question is interrupting if the pitch is decide by the time period ,so what is the frequency of a sound wave determines its?thank you so much for those videos it is really really helpful!

  13. Thank youu so muchh! it was veryy helpful 😀
    However i freaked out when i heard the gun shot HAHA i wasnt expecting that at all

  14. Transverse and longitudinal waves: 0:09
    Time period and frequency: 1:21
    Wave equation: 2:31
    Diffraction: 4:01
    Electromagnetic spectrum: 5:08
    Mirrors: 6:58
    Refraction: 9:12
    Total internal reflection: 12:25
    Prisms: 14:03
    Digital signals: 15:03
    Sound: 16:13
    Oscilloscope sound traces: 17:54

  15. "I can't claim credit for this mnemonic, it was invented by one of my students"
    well played ben, well played….

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