# Physics - P1.5 - Waves

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## P1.5.1 - The Nature of Waves

• Waves - used to transfer energy and information, direction of travel = direction wave transfers energy
• Different types of waves:
• transverse wave - oscillation of particles is perpendicular to direction wave travels
• longitutinal wave - oscillation of particles is parallel to waves travel direction, made up of compressions and rarefactions
• electromagnetic waves - light and radio waves, travel through vacuum, no particles - waves are oscillations in electric and magnetic fields, oscillation is perpendicular to direction wave travels - tranverse waves
• mechanical waves - waves on springs, and sound waves, travel through a medium - transverse or longitudinal
• Sound waves are longitudinal waves
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## P1.5.2 - Measuring Waves

• Amplitude - height of wave crest, or depth of wave trough, from rest position, greater amplitude = more energy carried
• Wavelength - transverse: distance from one crest, or trough, to the next, longitutinal: middle of one compression, or rarefaction, to the middle of the next
• Frequency - transverse: number of wave crests passing a point in one second, longitudinal: number of compressions passing a point in one second, unit - hertz (Hz) - equivilant to per second (s)
• Speed of wave - v = f x λ
• v - wave speed - m/s
• f - frequency - Hz
• λ - wavelength - m
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## P1.5.3 - Wave Properties: Reflection

• Image seen in a mirror is due to reflection of light
• Incidence ray - goes towards the mirror
• Reflected ray - goes away from mirror
• Normal - perpendicular to mirror, at the point incidence ray hits mirror
• Angle of incidence - angle between incidence ray and normal
• Angle of reflection - angle between reflected ray and normal
• Any reflected ray - angle of incidence = angle of reflection
• Image in a plane mirror is: same size, upright, same distance behind mirror, virtual
• Real image - can be formed on a screen - rays of light that produce image actually pass through it
• Virtual image - can't be formed on a screen - rays of light that produce image only appear to pass through it
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## P1.5.4 - Wave Properties - Refraction

• Waves change speed and wavelength when cross a boundary between different substances, frequency stays the same
• Refraction - property of all waves, including light and sound
• Change in speed of the waves causes change in direction
• Light enters more dense substance - slows down, changes direction towards normal
• Light enters less dense substance - speeds up, changes direction away from normal
• If wave is travelling along normal it won't change direction
• Different colours of light - different wavelength and refracted by slightly different amounts - when white light is shone onto a triangular prism, spectrum is produced - dispersion
• Violet light refracted most, red light refracted least
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## P1.5.5 - Wave Properties: Diffraction

• Diffraction - property of all waves, including light and sound - spreading of waves when passing through a gap or around an obstacle
• Effect is most noticable if wavelength of wave = size of gap or obstacle
• TV signals carried by radio waves - people living in hilly areas may not receive signal as a hill is blocking it - radio waves passing the hill will be diffracted around the hill - don't diffract enough = poor radio or TV signal
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## P1.5.6 - Sound

• Casued by mechanical vibrations
• Travels as a wave through solids, liquids and gases - fastest in solids and lowest in gases - can't travel through a vacuum
• Longitudinal waves, direction of vibration = direction of travel
• Range of frequences heard by humans - 20-20000Hz - decreases with age
• Reflected to produce echoes - only hard, flat surfaces reflect sound, soft things absorb sound, an empty room will sound different once things are put in it
• Refraction takes place at boundaries between layers of air at different temperatures
• Sound waves can also be diffracted
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## P1.5.7 - Musical Sounds

• Pitch depends on frequency of sound waves - higher frequency = higher pitch
• Loudness depends on amplitude of sound waves - greater amplitude = more energy carried by wave = louder sound
• Differences in waveform can be shown on an oscilloscope
• Tunng forks and signal generators produce 'pure' waveforms - quality of note depends on waveform
• Different instruments = different waveforms - sound different
• Vibrations created in an instrument when it's played produce sound waves
• In some instruments, a column of air vibrates, others, a string vibrates, some instruments vibrate when struck
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