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P1.5 The Use Of Waves
For Communication
- P1.5.1 General Properties Of Waves
- Waves transfer energy and may be
either transverse or longitudinal. In a
transverse wave the oscillations are
perpendicular to the direction of
energy transfer. In a longitudinal
wave the oscillations are parallel to
the direction of energy transfer.
- Electromagnetic waves are transverse, sound waves are
longitudinal and mechanical waves may be either
transverse or longitudinal. All types of electromagnetic
waves travel at the same speed through a vacuum (space).
Electromagnetic waves form a continuous spectrum.
- As waves travel, they set up patterns of disturbance. The amplitude
of a wave is its maximum disturbance from its undisturbed position.
The wavelength of a wave is the distance between a point on one
wave and the same point on the next wave. The 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 speed of a wave is related to its frequency
and wavelength, according to this equation: v = f
× λ where v is the wave speed in metres per
second, m/s, f is the frequency in hertz, Hz and λ
(lambda) is the wavelength in metres, m.
- Longitudinal waves
show areas of
compression and
rarefaction.
- Waves can be reflected, refracted and diffracted.
Significant diffraction only occurs when the wavelength
of the wave is of the same order of magnitude as the
size of the gap or obstacle. Waves undergo a change of
direction when they are refracted at an interface.
- Radio waves, microwaves, infrared and visible
light can be used for communication.These waves
are typically used as: radio waves – television, and
radio (including diffraction effects); microwaves –
mobile phones and satellite television; infrared –
remote controls; visible light – photography.
- Radio waves, microwaves, infrared and visible
light can be used for communication.These waves
are typically used as: radio waves – television, and
radio (including diffraction effects); microwaves –
mobile phones and satellite television; infrared –
remote controls; visible light – photography.
- Waves can be reflected, refracted and diffracted.
Significant diffraction only occurs when the wavelength
of the wave is of the same order of magnitude as the
size of the gap or obstacle. Waves undergo a change of
direction when they are refracted at an interface.
- Longitudinal waves
show areas of
compression and
rarefaction.
- The speed of a wave is related to its frequency
and wavelength, according to this equation: v = f
× λ where v is the wave speed in metres per
second, m/s, f is the frequency in hertz, Hz and λ
(lambda) is the wavelength in metres, m.
- As waves travel, they set up patterns of disturbance. The amplitude
of a wave is its maximum disturbance from its undisturbed position.
The wavelength of a wave is the distance between a point on one
wave and the same point on the next wave. The 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.
- Electromagnetic waves are transverse, sound waves are
longitudinal and mechanical waves may be either
transverse or longitudinal. All types of electromagnetic
waves travel at the same speed through a vacuum (space).
Electromagnetic waves form a continuous spectrum.
- Waves transfer energy and may be
either transverse or longitudinal. In a
transverse wave the oscillations are
perpendicular to the direction of
energy transfer. In a longitudinal
wave the oscillations are parallel to
the direction of energy transfer.
- P1.5.2 Reflection
- The normal is a
construction line
perpendicular to the
reflecting surface at the
point of incidence. The
angle of incidence is equal
to the angle of reflection.
The image produced in a
plane mirror is virtual.
- The normal is a
construction line
perpendicular to the
reflecting surface at the
point of incidence. The
angle of incidence is equal
to the angle of reflection.
The image produced in a
plane mirror is virtual.
- P1.5.3 Sound
- Sound waves are longitudinal waves and cause vibrations
in a medium, which are detected as sound. The pitch of a
sound is determined by its frequency and loudness by its
amplitude. Echoes are reflections of sounds.
- Sound waves are longitudinal waves and cause vibrations
in a medium, which are detected as sound. The pitch of a
sound is determined by its frequency and loudness by its
amplitude. Echoes are reflections of sounds.
- P1.5.4 Red-shift
- If a wave source is moving relative to an observer there will be a change in the observed
wavelength and frequency. This is known as the Doppler effect. The wave source could be
light, sound or microwaves. When the source moves away from the observer, the observed
wavelength increases and the frequency decreases. When the source moves towards the
observer, the observed wavelength decreases and the frequency increases.
- There is an observed increase in the wavelength of light from most distant galaxies. The further away the
galaxies are, the faster they are moving, and the bigger the observed increase in wavelength. This effect is
called red-shift. The observed red-shift provides evidence that the universe is expanding and supports
the 'Big Bang' theory (that the universe began from a very small initial point).
- Cosmic microwave background radiation (CMBR) is a form of
electromagnetic radiation filling the universe. It comes from
radiation that was present shortly after the beginning of the
universe. The 'Big Bang' theory is currently the only theory that
can explain the existence of CMBR.
- Cosmic microwave background radiation (CMBR) is a form of
electromagnetic radiation filling the universe. It comes from
radiation that was present shortly after the beginning of the
universe. The 'Big Bang' theory is currently the only theory that
can explain the existence of CMBR.
- There is an observed increase in the wavelength of light from most distant galaxies. The further away the
galaxies are, the faster they are moving, and the bigger the observed increase in wavelength. This effect is
called red-shift. The observed red-shift provides evidence that the universe is expanding and supports
the 'Big Bang' theory (that the universe began from a very small initial point).
- If a wave source is moving relative to an observer there will be a change in the observed
wavelength and frequency. This is known as the Doppler effect. The wave source could be
light, sound or microwaves. When the source moves away from the observer, the observed
wavelength increases and the frequency decreases. When the source moves towards the
observer, the observed wavelength decreases and the frequency increases.
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