# Book Reference : Pages 174-175

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16 Νοε 2013 (πριν από 5 χρόνια και 1 μήνα)

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1.
To understand some common sources of
waves

2.
To understand the differences between
longitudinal and transverse waves

3.
To understand properties which are common
to all waves

Book Reference : Pages 174
-
175

There are many different types of waves but
broadly they can be split into two types:

Mechanical Waves :

These require a medium to travel through : Examples
include sound, water waves and seismic waves. They all
require a medium for vibration to be transmitted.

Electromagnetic Waves :

Vibrating electromagnetic fields which are able to travel
through space without the need for a medium. Examples
include light, radio waves, microwaves and X
-
rays

In Longitudinal waves the direction of vibration is
parallel

to the direction of wave travel

Direction of travel
(Propagation)

Examples include : Sound waves & Primary
seismic waves

Dir
e
ction of vibration

In Transverse waves the direction of vibration is
perpendicular
to the direction of wave travel

Direction of travel
(Propagation)

Examples include : All electromagnetic waves &
Secondary seismic waves

Dir
e
ction of

vibration

The
displacement

of a vibrating particle is its
distance and direction from the equilibrium
position

The
Amplitude

is the maximum displacement. For
a transverse wave this is the maximum height of
the wave crest or trough. It can be thought of in
terms of energy, power, volume or loudness

The
wavelength

is the distance in metres
between the same point on two successive waves

The top of the wave is called the
crest

The bottom of the wave is called the
trough

The
frequency

of a wave is the number of
complete cycles per second. Units are Hertz (Hz)

The
Period

T,
(measured in
seconds)

of a
wave with
frequency
f

is
the time for one
complete wave
and is given by

T = 1/f

We have seen that there is a strong relationship
between wavelength and frequency. As you increase
one the other reduces in proportion. There is a
relationship between the two...

This is the speed of the wave which is given by:

Wave speed(m/s) = frequency(Hz) x wavelength (m)

c = f

With transverse waves the displacement is perpendicular
to propagation.... There is still a further dimension to
consider : The wave can vibrate up
-
down or left
-
right and
everything in between

Further examples

Polarised sunglasses reduce reflected glare

Light from the original
source is likely to be
unpolarised
. However,
annoying reflections from
water and glass are likely
to be polarised and can
be removed with a filter