all waves transfer energy without transferring matter oscillations or vibrations are passed along instead of the particles themselves longitudinal waves are those in which the direction of the oscillations is parallel to the direction of energy transfer that is the direction the wave is going examples of these are sound waves and seismic p waves P stands for primary because they're fast in these waves particles Bunch up we call those compressions and when they're spread out we call those rare refractions transverse waves are those in which the direction of oscillations is perpendicular to to the direction of energy transfer they wiggle side to side or up and down examples are waves on the surface of water seismic S waves secondary they're slower than p waves they produce earthquake after shocks and light and also every other em electromagnetic wave too we can represent any wave including longitudinal waves like this we call this a waveform displacement is up the y- Axis basically just how far the particles have oscillated from their original position and it can be either distance or time on the x-axis the peak of a is called the amplitude it's the maximum displacement from equilibrium if it's distance on the x-axis one complete wave here gives you the wavelength we give this the symbol Lambda for short but it's measured in meters if it's time on the x-axis instead one complete wave gives you the time period capital T for short this is the time it takes for one complete wave to pass measured in seconds frequency on the other hand is how many waves pass a point every second and the unit is Hertz so frequency and time period are the opposite in fact they're reciprocals of each other so we can say frequency is equal to 1 over time period FAL 1/ T you can often be asked to find frequency from a wave form like this measure the time period Then do one divided by that easy the wave equation is this V equal F Lambda that's wave speed equals frequency time wavelength a ripple tank will tell you what frequency is made you can measure the distance between 10 Peaks then divide by 10 to get the wavelength say and just use the wave equation to get the speed of the wave you could also just time how long it takes for a ripple in a tray of water to travel the length of the tray 10 times then just do total distance the V by time to get speed instead the speed of sound waves can be measured by attaching a microphone up to oscilloscope for example if you clap once next to the microphone the sound can Echo off a wall un known distance away and it comes back to the microphone then you can just use the oscilloscope to measure the time it took to travel then do total distance divided by time again just for triple sound waves cause the air drum to vibrate which in turn is converted into a signal that travels to your brain the human ear can hear frequencies between 20 Herz and 20 khz 20,000 HZ any frequency Above This is called ultrasound whenever Sound reaches a boundary between two different mediums materials some of it goes through we say it's transmitted while some is reflected this is the case when we emit ultrasound into a person's body and a computer can time how long it takes to return off different layers allowing it to build up an image of what's inside this allows us to scan baby safely we can also time sound waves in water to build up a picture of what's under a boat or around a submarine this is called Sona we've mentioned seismic waves already but you also need to know that while the longitudinal p waves can travel through liquids transverse S waves cannot that's how we've come to believe that the Earth has a molten core there's no Aftershock felt when an earthquake happens on the other side of the earth which implies that there must be a liquid Center when waves reflect off a smth smooth surface we say that's specular reflection that just means not scattered like a mirror the angle of incidence will be equal to the angle of reflection all angles are measured from the normal which is a line we draw perpendicular to the surface if light is scattered off a rough surface we call this diffuse reflection instead em or electromagnetic waves are for everybody they're special because they don't need a medium to travel through they're the only waves that can travel through the vacuum of space there are a range of wavelengths in the em Spectrum which we split up into these sections radio waves microwaves infared radiation visible light ultraviolet x-rays gam if you haven't heard the original version It's a certified Banger Link in description EM waves are produced when electrons lose energy they lose the energy as an EM wave the higher the frequency the more energy the wave carries and the shorter the wavelength The Only Exception are gamma rays which are actually emitted by nuclei instead that means lots more energy is involved that's why they're dangerous they are all however absorbed by electrons this allows our retina to detect light for example phone antennas to receive radio signals and your face to absorb infrared from the Sun and feel heat UV X-rays and gamma rays carry so much energy though that they can cause electrons to leave their atoms the atoms have been ionized that can be dangerous if absorbed by DNA and cells as this can cause mutations that can lead to cancer while some Ian waves can be dangerous we use all parts of the spectrum for communications cooking heating Imaging Medical Treatments and more when light waves move from one medium to another say from Air to Glass they change speed in this case the wave slows down and the wavelength also decreases instead of drawing the wave fronts from above like what you see above water we can just draw a ray to show the direction the light is moving in that's a lot easier a change in medium also results in a change in Direction This is called refraction that is if it's at an angle to the normal the line we draw perpendicular to the surface you can think of light always wanting to get away from the normal but never write that in the exam if light slows down it moves closer to the normal so that means that the angle of refraction is smaller than the angle of incidence that's the angle that it hits the surface at now all of these angles are measured from the normal that means you must have your protractor with the zero on the normal never have it flat on the surface it's always perpendicular to the surface the rest of waves is triple only so skip to magnetism if you're double lenses oh boy here we go okay lenses are curved blocks of glass Al see you have them in your eyes they use refraction to make rays of light converge meet or diverge spread out a convex lens can make Rays converge this is the symbol we use to represent it if Rays enter parallel to what we call the principal axis for example the light from an object very far away the lens will make the Rays converge at this point here this is called the principal Focus the distance from the center of the lens is called the focal length this doesn't change for a lens and we can draw it on both sides and you'll see why in a bit however light doesn't usually come from objects infinitely far away but from objects a little bit nearer the object could be anything but we often represent it with just an arrow convex lens can then project an image using the light that comes from the object but we only consider the light coming from the top of the object and we can do that by drawing two rays one always goes straight through the center of the lens and one goes parallel into the lens then through the principal Focus where these two rays meet is where the image is formed that's where you want your projector screen or retina or camera sensor to be in order to get a clear image formed you'll also notice that the image is smaller than the object so we say it's diminished it's also upside down so we say it's inverted things get a bit trickier when the object is very close close to the lens now the Rays don't meet the image can't be projected however if we extrapolate the two rays back behind the lens they do meet we can draw the image here and we can say that it's magnified it's upright but it's virtual that means that it can't be projected it's no longer a real image like we had before this would be what a magnifying glass does for example your eye can deal with this diverging light accordingly to make it focus on your retina but that means that you see this magnifying virtual image so things appear bigger concave lenses always diverge like Rays so they always produce a virtual image with these our line parallel in goes back through the other principal Focus behind the lens where it meets the other Ray is where the virtual image is this image is also diminished and upright as you can see the magnification of a lens is just the ratio of image height to object height a magnification greater than one means the image is bigger than the object less than one it it's diminished it's smaller than the object what we perceive as color is a result of different wavelengths of light being emitted by a source or reflected by an object that are then absorbed by the cells in our retina most objects will absorb some wavelengths of light while reflect others for example chlorophyll in Plants absorbs longer red wavelengths of Light which is why leaves appear green it reflects those shorter wavelengths this ball looks blue in sunlight because it reflects the blue wavelengths of light shine just red light light on it though and it will appear black as that red light will be absorbed no light will be reflected no idea whether this is gcsc but here we go a black body is an object that perfectly absorbs and emits all wavelengths of radiation while there's no such thing in reality it's a useful concept that we can apply to some objects like stars or planets if a body or object absorbs radiation at a greater rate than it's emitting it its temperature will increase but if the temperature increases that also means that it starts emitting radiation at a greater rate too so I hope you found that helpful leave a like if you did and pop any questions or comments below I'll see you in the next video