The speed of a pulse in a medium depends on:
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The tension in the medium i.e. the higher the tension, the faster the pulse moves
The density of the medium i.e. a pulse travels faster in a lighter rope than in a heavy
rope
Reflection and transmission of a pulse
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If a pulse moves along a rope which is fixed at one end e.g. attached to a wall, the
pulse will be reflected and inverted
The speed and wavelength of the incident and reflected pulse will be the same
The amplitude of the reflected pulse is less because some energy is lost into the wall
Reflection of a pulse at a free end
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If a pulse moves along a rope which is free (loose) at one end, the pulse will be
reflected but not inverted
The speed and wavelength of the incident and reflected pulse will be the same
The amplitude of the incident and reflected pulse will also be the same since no
energy is lost into the wall
Movement of a pulse from a thin rope into a thick rope
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The incident pulse is partly reflected and partly transmitted – the reflected pulse will
be inverted
The wavelength of the reflected pulse is the same as for the incident pulse but its
amplitude is smaller (Why?)
The wavelength of the transmitted pulse is shorter and it moves slower than the
reflected pulse.
From a thick rope to a thin rope
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The incident pulse is partly reflected and partly transmitted – the reflected pulse will
not be inverted
The wavelength of the reflected pulse is the same as for the incident pulse but its
amplitude is smaller (Why?)
The wavelength and speed of the transmitted pulse is more.
Superposition
When a pulse in a medium meets at the same point simultaneously, the
instantaneous displacement at that point is equal to the algebraic sum of the
displacement of each pulse at that moment.
It can either be:
Constructive Interference
When 2 pulses meet on the same side of the rest position to form a much bigger
pulse at that point
Destructive Interference
When 2 pulses meet on the opposites sides of the rest position to form a smaller or
no pulse at that point
Standing waves
It is formed when two identical series of pulses move in opposite directions in the
same medium, so that constructive and destructive interference takes place at
different points.
e.g. incident and reflected waves with the same amplitude, wavelength and speed
moving in opposite directions
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At the antinodes (A), constructive interference occurs, to produce maximum
displacement
At the nodes (N), destructive interference occurs, to produce zero displacement