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Waves Pt1
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- 1What are waves?Waves are vibrations that transfer energy from place to place without matter (solid, liquid or gas) being transferred.
- 2Seismic WavesShock waves travelling through the Earth, usually caused by an Earthquake
- 3Some waves must travel through a substance...The substance is known as the medium and it can be solid, liquid or gas. Sound waves and seismic waves are like this. They must travel through a medium, and it is the medium that vibrates as the waves travel through
- 4Electromagnetic RadiationEnergy travelling as waves in the form of changing electrical and magnetic fields
- 5MicrowavesElectromagnetic radiation with a frequency between that of visible light and radio waves
- 6Other waves do not need to travel through a substance...They may be able to travel through a medium, but they do not have to. Visible light, infrared rays, microwaves and other types of electromagnetic radiation are like this. They can travel through empty space. Electrical and magnetic fields vibrate as the waves travel.
- 7Transverse WavesIn transverse waves, the oscillations (vibrations) are at right angles to the direction of travel and energy transfer
- 8Types of Transverse WavesLight and other types of electromagnetic radiation are transverse waves. All types of electromagnetic waves travel at the same speed through a vacuum, such as through space. Water waves and S waves (a type of seismic wave) are also transverse waves.
- 9Longitudinal WavesIn longitudinal waves, the oscillations (vibrations) are along the same direction as the direction of travel and energy transfer.
- 10Types of Longitudinal WavesSound waves and waves in a stretched spring are longitudinal waves. P waves (relatively fast moving longitudinal seismic waves that travel through liquids and solids) are also longitudinal waves.
- 11Longitudinal waves show area of compression and rarefactionIn a spring the areas of compression are where the parts of the spring are close together, while the areas of rarefaction are where they are far apart.
- 12AmplitudeAs waves travel, they set up patterns of disturbance. The amplitude of a wave is its maximum disturbance from its undisturbed position. Take care: the amplitude is not the distance between the top and bottom of a wave.
- 13Amplitude and Wavelength of a Transverse Wave
- 14WavelengthThe wavelength of a wave is the distance between a point on one wave and the same point on the next wave. It is often easiest to measure this from the crest of one wave to the crest of the next wave, but it doesn't matter where as long as it is the same point in each wave.
- 15FrequencyThe frequency of a wave is the number of waves produced by a source each second. It is also the number of waves that pass a certain point each second. The unit of frequency is the hertz (Hz). It is common for kilohertz (kHz), megahertz (MHz) and gigahertz (GHz) to be used when waves have very high frequencies.
- 16Radio WavesLow frequency electromagnetic radiation used to transmit information such as television and radio programmes
- 17Wave SpeedThe speed of a wave is related to its frequency and wavelength, according to this equation:
v = f × λ
v is the wave speed in metres per second, m/s
f is the frequency in hertz, Hz
λ is the wavelength in metres, m. - 18Example of Wave SpeedAll waves obey this wave equation. For example, a wave with a frequency of 100 Hz and a wavelength of 2 m travels at 100 × 2 = 200 m/s.
- 19RefractionSound waves and light waves change speed when they pass across the boundary between two substances with different densities, such as air and glass. This causes them to change direction and this effect is called refraction.
- 20There is one special case you need to know...Refraction doesn't happen if the waves cross the boundary at an angle of 90° (called the normal) - in that case they carry straight on.
- 21DiffractionWhen waves meet a gap in a barrier, they carry on through the gap. However, the waves spread out to some extent into the area beyond the gap. This is called diffraction. The extent of the spreading depends on how the width of the gap compares to the wavelength of the waves.
- 22Significant diffraction only happens when the wavelength is of the same order of magnitude as the gap. For example:a gap similar to the wavelength causes a lot of spreading with no sharp shadow, eg sound through a doorway
a gap much larger than the wavelength causes little spreading and a sharp shadow, eg light through a doorway. - 23ReflectionSound waves and light waves reflect from surfaces. When waves reflect, they obey the law of reflection
- 24Law of Reflectionthe angle of incidence equals the angle of reflection
The normal is a line drawn at right angles to the reflector
The angle of incidence is between the incident (incoming) ray and the normal
The angle of reflection is between the reflected ray and the normal. - 25Law of Reflection2Smooth surfaces produce strong echoes when sound waves hit them, and they can act as mirrors when light waves hit them. The waves are reflected uniformly and light can form images. Rough surfaces scatter sound and light in all directions. However, each tiny bit of the surface still follows the rule that the angle of incidence equals the angle of reflection.
- 26The waves can:appear to come from a point behind the mirror, for example a looking glass
be focused to a point, for example sunlight reflected off a concave telescope mirror - 27—In a ray diagram, the mirror is drawn a straight line with thick hatchings to show which side has the reflective coating. The light rays are drawn as solid straight lines, each with an arrowhead to show the direction of travel. Light rays that appear to come from behind the mirror are shown as dashed straight lines.
- 28Construction of Ray DiagramsMake sure that the incident rays (the solid lines) obey the law of reflection: the angle of incidence equals the angle of reflection. Extend two lines behind the mirror. They cross where the image appears to come from.
- 29The image in a plane mirror is:virtual (it cannot be touched or projected onto a screen)
upright (if you stand in front of a mirror, you look the right way up)
laterally inverted (if you stand in front of a mirror, your left side seems to be on the right in the reflection).
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- GCSE Physics Fichas sobre Waves Pt1, creado por Kiera Ashford el 17/04/2017.
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- Kiera Ashford
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