1. Introduction to waves - what are they? and types of
waves?
Be able to describe that waves transfer energy and information without
transferring matter.
Waves are vibrations of a material e.g.
sound or oscillations of an electromagnetic field e.g. visible light.
With transverse
waves the oscillations are at right angles to the direction the
wave is travelling.
A transverse wave has an 'up and down' component in its
description.
With longitudinal
waves the oscillations are in the same direction as the wave is
travelling.
A longitudinal wave has an 'to and fro' component in its
description.
Waves have energy and can transfer it from
one place to another.
This means waves can carry
information by changing the energy of the wave in a sequential way to
transfer 'data' from one place to another, but waves cannot transfer
the matter of the medium they are moving though - the medium can be
gas, liquid or solid.
Electromagnetic radiation
does not need a medium, it can travel through vacuum
as well
as transparent gases (e.g. air), liquids (e.g. water) or solids
(e.g. glass).
Infrared and visible light beams in
fibre optic cables can carry enormous amounts of information often as
telephone calls or the networks of the internet - the information is
converted to binary code and the 'pulsed code' is imposed on, and
transferred by, the visible or infrared carrier wave.
When the signals reach your
mobile phone or computer, they are decoded and presented in an
audio-visual way.
When your TV receives the signal, its just
coded data in the electromagnetic wave, energy is transferred, but no material substance arrives!
However, if energy itself
wasn't transmitted, no effect could be produced on the TV screen without
something from the receiver!
Similarly, when ripples on water cause
floating objects to bob up and down, energy is needed to do this, but
neither the floating object or the water itself actually move in the
direction of the transverse waves - but energy is transferred from one
location to another.
The most dramatic transfer of energy
involves seismic earthquake waves, both transverse and longitudinal, yet the effects
are transmitted and felt miles from the epicentre and no part of the earth's
crust moves in the direction of the seismic waves but it may move violently
from side to side, up and down or compressed/decompressed.
When sound waves vibrate your ear drum no
air moves from the TV, person or musical instrument to your ear, yet energy is
transferred, carried by vibrations, through the medium of air, otherwise, what
could cause your ear drum
to vibrate!
You need to know the two formulae for waves
relating them to wavelength, frequency, speed and distance travelled and
calculations and problem solving based on them.
speed = distance / time
and speed = wavelength x frequency
Know the differences between longitudinal and transverse waves by referring to
sound, electromagnetic and seismic waves.
You need to understand that in a
transverse wave the oscillations are perpendicular (at 90o) to the direction of
energy transfer, but in a longitudinal wave the oscillations are parallel to
the direction of energy transfer ie direction of forward wave movement.
Transverse wave diagram
Shaking a slinky spring from
side to side (at 90o to stretched out spring) in a regular
rhythm produces a transverse wave of energy pulses.
Similarly wave ripples on water and all
electromagnetic radiation waves oscillate at 90o to the direction
the wave is travelling.
Longitudinal wave diagram
Pulling and pushing on a slinky
spring in a regular rhythm produces pulses of energy transmitted as a longitudinal wave
down the stretched out spring.
Similarly a
sound wave is pulses of energy travelling through a medium - the 'compressions' and
'rarefactions' are in the same direction as the wave movement.
More on examples of waves in the
part 2
Check out your
practical work you did or teacher demonstrations you observed, all of this is part of good revision for your
end of course examination context questions and helps with 'how science works'.
using a class set of skipping ropes to investigate frequency and
wavelength,
demonstrating transverse and longitudinal waves with a slinky
spring,
carrying out investigations using ripple tanks, including the relationship
between depth of water and speed of wave,
INDEX notes: Investigating and introducing
the properties of waves
Keywords, phrases and learning objectives for
waves
Know, and be able to explain what waves are and
describe the two types of longitudinal waves and transverse waves in
terms of the direction of oscillations-vibrations and the fact that
they transfer energy.
Use your
mobile phone in 'landscape' mode?
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INDEX notes: Investigating and introducing
the properties of waves
