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Edexcel Physics IGCSE Topic 3: Waves Summary Notes (Content in ​bold​ is for physics only) This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0...

Edexcel Physics IGCSE Topic 3: Waves Summary Notes (Content in ​bold​ is for physics only) This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0 https://bit.ly/pmt-cc https://bit.ly/pmt- d https://bit.ly/pmt-cc General wave properties Waves ​transfer energy and information without transferring matter; ​the particles oscillate about a fixed point. Transverse​ waves o Have​ peaks​ and ​troughs o Vibrations are at ​right angles ​to the direction of travel o An example is light Longitudinal​ waves o Consists of compressions (particles pushed together) and rarefactions (particles moved apart) o Vibrations are in the ​same direction ​as the direction of travel o An example is sound Amplitude – the ​distance​ from the ​equilibrium​ position to the ​maximum displacement Wavefront – a line joining points on a wave at the same point in their wave cycle at a given time Frequency – the ​number of waves​ that pass a single point​ per second Wavelength – the ​distance​ between a ​point​ on one wave and the ​same point​ on the next wave Time period – the ​time taken ​for ​one complete wave ​to pass a fixed point The ​speed​ of a wave is equal to the product of the frequency and wavelength: speed = f requency×wavelength v = fλ The frequency of a wave is equal to the reciprocal of the time period, measured in ​Hertz (Hz): 1 f requency = time period f = T1 The Doppler Effect: If a wave source is ​moving relative ​to an observer, there will be a change​ in the ​observed frequency and wavelength ​due to the Doppler effect. ​This is because the wavefronts either get ​bunched together​ or ​spaced apart. ​An example of this is when the siren of an ambulance is high-pitched as it approaches you, and low-pitched as it goes away. Reflection: All ​waves can be ​reflected ​when they travel from a medium of low optical density ​(such as air) to one of much higher optical density (such as glass) The law of reflection states that: o Angle of incidence = angle of reflection Frequency, wavelength, and speed are all ​unchanged Refraction: All waves can be refracted, which is when the ​speed​ of a wave changes​ when it enters a new medium If the wave enters a ​denser​ medium, its speed ​decreases​ and it bends ​towards​ the normal If the wave enters a​ less dense​ medium, its speed ​increases and it bends ​away from​ the normal https://bit.ly/pmt-cc https://bit.ly/pmt- d https://bit.ly/pmt-cc  In all cases, the ​frequency​ stays the ​same​ but the ​wavelength changes.​ As a result, the velocity must change. Electromagnetic spectrum You need to learn the ​main groups ​of the electromagnetic spectrum in order of ​decreasing wavelength ​and ​increasing frequency ​including the ​colours​ of the visible spectrum (ROYGBIV). All electromagnetic waves travel with the ​same high speed​ in a vacuum and ​approximately the same​ speed in air. Uses of electromagnetic waves: Radio waves​ are used for ​radio and television communications.​ They have a long wavelength and are reflected by a layer of the atmosphere called the ​ionosphere​. Microwaves​ are used for ​satellite transmissions​ and in ​cooking.​ As they have a greater frequency (shorter wavelength) they are more penetrating so can pass through the ionosphere and penetrate deep into food. Infrared radiation​ is used in ​heaters ​and​ night vision equipment. Visible light ​is used in ​fibre optics ​and ​photography. Ultraviolet ​light is used in ​fluorescent lamps. X-rays​ are used in ​medical imaging ​and in ​security​ as (because they have a very short wavelength and high frequency) they can penetrate material easily. Gamma radiation​ is used in ​sterilising food and medical equipment ​due to its high energy. Hazards: Microwaves can cause ​internal heating​ of body tissues. Infrared radiation can cause ​skin burns. Ultraviolet light exposure increases the risk of​ skin cancer​ and ​blindness. o Sun cream ​and ​sun glasses ​prevent over-exposure in summer. X-rays and Gamma rays are ​ionising​ radiation that can cause ​mutations​ leading to cancer. o Exposure​ to these kinds of radiation should be ​minimised ​(for example, by using protective shielding made of very dense materials such as lead). https://bit.ly/pmt-cc https://bit.ly/pmt- d https://bit.ly/pmt-cc Light and sound Light​ waves are ​transverse​ waves and can be ​reflected​ and ​refracted. Reflection​ of light can be shown when light reflects at a plane mirror and forms an image. o This can be represented by a ​ray diagram​ like the first one shown on the right. Refraction​ of light can be shown when light is passed through a glass slab at an angle to its normal. o When light enters a more optically dense medium, the ​angle of incidence ​(the angle between the incident ray and the normal) is​ greater​ than the angle of refraction​ (the angle between the refracted ray and the normal). This can be represented by a ray diagram like the second one shown on the right. o The​ opposite​ is true when light enters a less optically dense medium. Snell's law​ relates the angle of incidence and the angle of refraction to the refractive index of a medium by n1sini = n2sinr where n is the optical density & i is the angle of incidence and r is the angle of refraction. Total internal reflection: At a certain angle of incidence called the ​critical angle​, the light will travel along the boundary between the two media. Total internal reflection​ occurs when the angle of incidence is greater​ than the critical angle and the light​ reflects​ back into the medium. For total internal reflection to occur, the light must also be travelling from a ​more optically dense medium​ into a ​less optically dense medium​ (most common example is glass to air). The critical angle c can be related to the refractive index by: 1 n= sin sin c Optical fibres: An ​optical fibre​ is a long thin rod of ​glass​ surrounded by cladding which uses total internal reflection to transfer information by light, even when bent. They are used extensively in ​medicine ​(endoscopes, inside-body flexible cameras) and communications​ (high speed data transfer). https://bit.ly/pmt-cc https://bit.ly/pmt- d https://bit.ly/pmt-cc Sound waves are ​longitudinal​ waves and can be ​reflected​ and ​refracted. The range of audible frequencies for a healthy human ear is 20 Hz to 20000 Hz. To measure the​ speed of sound ​in air, you can make a noise at a known, large​ distance​ from a solid wall and record the ​time​ for the ​echo​ (reflected sound) to be heard, then use speed = distance/time, where distance is 2 x length - taking into account the fact that the sound had to go there and back. An ​oscilloscope​ connected to a ​microphone​ can be used to display a sound wave and find its frequency and amplitude. The ​greater the amplitude​ of a sound wave, the ​louder​ it is. The​ greater the frequency​ of a sound wave, the ​higher its pitch. The first sound wave shown is quiet​ and ​low pitched. The second sound wave shown is ​loud ​and ​low pitched. The third sound wave shown is loud​ and ​high pitched. https://bit.ly/pmt-cc https://bit.ly/pmt- d https://bit.ly/pmt-cc