The World Communicates 1. The wave model can be used to explain how current technologies transfer information * describe the energy transformations required in one of the following: mobile telephone, fax/ modem, radio and television Energy transmission in mobile telephone: ound wave energy (input sound) -> electrical (in transmitting phone) – > radio wave (transmit signal) -> electrical (in receiving phone) -> sound (output sound) * describe waves as a transfer of energy disturbance that may occur in one, two or three dimensions, depending on the nature of the wave and the medium A wave is a travelling disturbance which transfers energy without transporting matter. They may occur in 1D, 2D or 3D, depending on the nature of the wave and the medium. D- slinky, laser light >>> only moves in one direction 2D- water wave >>> propagates in all directions on a single plane 3D-light, sound, all EM waves >>> spreads/ radiates in all directions from a single point *
identify that mechanical waves require a medium for propagation while electromagnetic waves do not Mechanical waves require a medium (particles in order to propagate) while electromagnetic waves do not. Classification of Waves: in terms of medium > mechanical (requires), electromagnetic (doesn’t require) -in terms of particle oscillation > mechanical >>> transverse (perpendicular), longitudinal (parallel) * define and apply the following terms to the wave model: medium, displacement, amplitude, period, compression, rarefaction, crest, trough, transverse waves, longitudinal waves, frequency, wavelength, velocity Mechanical Waves -require a medium to propagate -involves the transfer of energy through a medium by the motion of particles of the medium itself -particles moves as oscillations or vibrations around a fixed point
Transverse waves (e. g. light) - mechanical waves - particles of the medium oscillate back and forth in a direction perpendicular to the direction of wave propagation -does not require a medium Longitudinal/compressional waves (e. g. sound) -mechanical waves -particles of the medium oscillate back and forth in a direction parallel to the direction of propagation -requires a medium Period (T) – time taken for a single wave to pass through a fixed point OR the time taken for a particle of a medium to make one complete oscillation (measured in seconds) -T = 1f
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Frequency (f) – number of waves that pass through a fixed point per second OR number of complete oscillations of a medium particle in one second (measured in hertz > Hz) Medium – material through which a wave can propagate Displacement-shortest distance from initial position to final position of a particle Amplitude (A) – maximum displacement of particles from the undisturbed state (equilibrium position) Compression – zones where particles are closer together than in their undisturbed state Rarefaction – zones where the particles are further apart than in their undisturbed state Crest- highest part of the waves
Trough- lowest part of the wave Wavelength (? ) – distance between 2 successive identical points on a wave (e. g. distance measured in metres, between adjacent crests or troughs) Velocity (v) – speed at which the wave transfers energy away from the source * describe the relationship between particle motion and the direction of energy propagation in transverse and longitudinal waves Particles in a transverse wave oscillate back and forth in direction perpendicular to direction of propagation.
Particles in a longitudinal wave oscillate back and forth in direction parallel to direction of propagation. * quantify the relationship between velocity, frequency and wavelength for a wave: Velocity is directly proportional to the product of the frequency and wavelength of the wave. 2. Features of a wave model can be used to account for the properties of sound * identify that sound waves are vibrations or oscillations of particles in a medium Sound Waves -are vibrations or oscillations of particles in a medium classed as a mechanical longitudinal wave -when sound wave propagates, vibrations of the particles create pressure variations within that medium -frequency of a sound is determined by the frequency of the original vibration,
NOT by the medium it travels through (i. e. frequency of a sound doesn’t change through any medium) -speed of sound is different in different media -sound travels fastest in solids, followed by liquids then gases (i. e. higher density- particles packed more closely together- vibrations travel faster) -speed of sound in air = 343 m/s relate compressions and rarefactions of sound waves to the crests and troughs of transverse waves used to represent them Compressions > crests Rarefactions > troughs * explain qualitatively that pitch is related to frequency and volume to amplitude of sound waves The amplitude of a sound wave determines the volume of the sound. high amplitude = high volumelow amplitude=low volume Likewise, the frequency of a sound wave is directly related to the pitch of a sound. The higher the frequency, the more vibrations per second, and thus, the higher the pitch.
High frequency= high pitchlow frequency=low pitch * explain an echo as a reflection of a sound wave Echo - forms when a sound wave reflects off a hard surface and rebounds back to its original source, essentially becoming the reflection of a sound wave. - wide variety of applications including SONAR (Sound Navigation And Ranging) > method for finding the depth of water and detection of animals and other objects in water * describe the principle of superposition and compare the resulting waves to the original waves in sound Superposition- also known as wave interference when two or more waves of the same type pass through the same medium at the same time, they will interfere with each other -individual component waves will interfere to give the resultant wave -position of any point on the resultant wave is the sum of the amplitudes of the component waves -rules to superimpose component waves: 1. End points 2. Intersecting points 3. Crests/ Troughs -note: > curve + curve = curve gt; curve + line = curve > line + line = line > once component waves no longer interfere with each other, they will return to their initial state -constructive interference > component waves are in phase (crests and troughs aligned) -destructive interference > component waves 180? out of phase (crests of one wave aligned to troughs of the other and vice versa) > resultant wave is a straight line 3.
Recent technological developments have allowed greater use of the electromagnetic spectrum * describe electromagnetic waves in terms of their speed in space and their lack of requirement of a medium for propagation Electromagnetic Waves - travel through space at the speed of light, 3x10? m/s. - do not require a medium to propagate (i. e. can pass through a vacuum, are all transverse waves) - e. g. gamma rays, X-rays, ultraviolet, visible (VIBGYOR), infrared, microwaves, radio waves * identify the lectromagnetic wavebands filtered out by the atmosphere, especially UV, X-rays and gamma rays Waves able to penetrate atmosphere and reach surface of the Earth> visible light, radio waves, microwaves -too much exposure to UV radiation can result in cancers and dangerous mutations -too much exposure to X-rays and Gamma radiation would quickly kill us -Earth’s atmosphere has the ability to absorb ay incoming high energy radiation * identify methods for the detection of various wavebands in the electromagnetic spectrum EM Wave| Detectors| Source|
Gamma| Geiger Muller tube| Nuclei of radioactive atoms and cosmic rays| X-ray| Fluorescent screen| X-ray tubes| Ultraviolet (UV)| Photo/solar cellsFluorescent chemicals| Very hot objectsArcs and sparksMercury capour lamps| Visible| Photo/ solar cellsEye| Hot objectsLampsLasers| Infrared| Special photographic filmSkinSemiconductor devices such as LDR and photodiode| Warm and hot objects (e. g. ire, people)| Radio/ Microwaves| Aerials connected to tuned electric circuits in radio and TV sets| Microwaves and ovensTV and radio transmitters using electric circuits and aerialsOscillating electrons| Note: the sun is a producer of all EM waves sending all bandwidths to Earth Photographic film detects all EM waves except for radio/ microwaves * where k = amount of energy of source, d = distance away from source, I= intensity explain that the relationship between the intensity of electromagnetic radiation and distance from a source is an example of the inverse square law:
Intensity – the energy received per square metre per second at a distance away from the source Attenuation – decrease in the strength of the signal or light -EM waves decrease in intensity the further they are away from the source - to reduce attenuation in long distance communication, signal needs to be either: > sent out as a very large strong signal > signals travelling long distances need to be amplified at repeater or booster stations along their path * outline how the modulation of mplitude or frequency of visible light, microwaves and/or radio waves can be used to transmit information Bandwidth – space taken up in terms of frequency Modulation – process of adding (encoding) signal information to an EM wave Amplitude Modulation -signal wave encoded onto carrier wave by adding amplitude of signal wave and carrier waves using principle of superposition -turns into resultant modulated wave -information stored in variations of amplitude -constant frequency, changing amplitudes when received, radio receiver will decode variation in amplitude to obtain original signal, which is then amplified Advantages| Disadvantages| * requires a much smaller bandwidth of frequencies for transmission * number of transmissions possible in the AM band is larger| * depend on changing of amplitude through superposition of waves and therefore e very prone to interference |
Frequency Modulation -signal wave added to carrier waves by changing frequency of carrier wave -information stored in variations of frequency -constant amplitude, changing frequencies low signal corresponds to low frequency and vice versa for high signals Note: frequency bands = megahertz (MHz)= _x10^6 m/s Advantages| Disadvantages| * since FM waves store information on varying frequencies, less prone to interference -harder to influence frequency of a wave by interference and superposition| * each transmission utilises a large bandwidth * different transmitters must be allocated different frequency bands for transmission to avoide interference with each other * limited number of transmitters allowable in given area| discuss problems produced by the limited range of the electromagnetic spectrum available for communication purposes -each transmission requires different frequency bands, but available bandwidth for certain types of EM waves is limited so there’s a possibility may run out of bandwidth and have transmissions start interfering with each other 4. Many communication technologies use applications of reflection and refraction of electromagnetic waves * describe and apply the law of reflection and explain the effect of reflection from a plane surface on waves Reflection – When a wave strikes a boundary, it bounces back.
This is known as the reflection of a wave. Law of Reflection: - angle of incidence is equal to the angle of reflection - incident ray, reflected ray and the normal are on the same plane * describe ways in which applications of reflection of light, radio waves and microwaves have assisted in information transfer Light > fibre optic communcation Radio waves > AM/ FM radio transmission Microwaves > microwave repeating stations (to boost intensity of received signals through use of parabolic concave surface of satellite dishes) > mobile phone, internet cable data describe one application of reflection for each of the following: plane surfaces, concave surfaces, convex surfaces, radio waves being reflected by the ionosphere Plane > dressing and shaving Parabolic concave > satellite dishes (to reflect incoming signals to an antenna at the focus, hence amplifying signal), used in microwave repeating stations and radar control towers to boost intensity of received signals) >produce parallel beams of light used in torches, car headlight, etc Convex > shop security mirrors and side view mirrors (provides wider range of view) Radio waves reflected by ionosphere
Ionosphere – region of Earth’s atmosphere which consists of charged particles (electrons and ions) -charged property allows it to reflect low frequency (high wavelength) EM waves such as radio waves -this reflection property enables the transmission of radio waves to receivers that are ‘out of sight’ due to the Earth’s curvature * explain that refraction is related to the velocities of a wave in different media and outline how this may result in the bending of a wavefront Wavefront – a line that joins all the point that are in phase in a wave (e. . a line that joins all crests, so is perpendicular to direction of propagation) Refraction – when waves travel from one medium to another, where they experience a change in speed, travel different distances (for the same interval of time), causing its wavefronts to bend. This changes the direction of propagation of the wave. Exception – when wave hits boundary between the two media at right angles, incident wavefronts are parallel to boundary, or incident angle is 0? -wavelength and velocity change -frequency remains the same
When a wave travels from a more dense to a less dense medium, direction of wave bends away from the normal and vice versa. Note: deep water is less dense than shallow water * define refractive index in terms of changes in the velocity of a wave in passing from one medium to another Refractive Index – the absolute refractive index of a material is a ratio of the speed of light in a vacuum to the speed of light in the material RI = cv , where c is the speed of light, and v is the speed of light in material It is the change in velocity of a wave passing from one medium to another. related to optical density (i. e. high RI = high OD and vice versa) * define Snell’s Law: = ???? = n? n? * identify the conditions necessary for total internal reflection with reference to the critical angle Total internal reflection occurs when the incidence angle is greater than the critical angle. * i. e. boundary totally reflects the waves, hence the wave never escapes the medium it is in Critical angle: - wave travelling from more dense to less dense - angle of incidence forms an angle of reflection of 90? the critical angle) * outline how total internal reflection is used in optical fibres Fibre-Optic Communication - optic fibres made of glass or plastic materials -An optical fibre consists of a core (made of material with higher RI/ is more optically dense) and a cladding - Light encoded with data is guided along the length of the fibre via total internal reflection until it reaches the other end where the information is extracted and decoded Advantages| How/ Why| large amount of data can be transmitted at any one time * suitable for transmitting information where straight line transmission is impossible * interferences by outside disturbances are minimised since light waves are confined within fibres * energy lost due to long distance transmission minimised| * by using a group of many fibres * light waves only travel in straight lines * light waves are confined within fibres * energy of light waves totally trapped within core of fibres| . Electromagnetic waves have potential for future communication technologies and data storage technologies * identify types of communication data that are stored or transmitted in digital form * fibre optic communication * AM/FM radio broadcasting * mobile telephone calls * satellite communication
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