What we will do today:
• Define the two forms of waves using
‘slinky’s’.
• Identify the following wave
characteristics from a wave:
wavelength, amplitude, frequency and
period.
Types of wave
•
There are two forms of wave
movement:
1. Transverse waves
2. Longitudinal waves
Slinky drop in slow motion
http://www.youtube.com/watch?v=r
Cw5JXD18y4
1. Transverse Waves
•
•
•
Transverse waves are waves whose vibrations
(energy) moves in an “up and down” motion.
We say they are ‘at right angles to the wave
direction’.
Example of transverse waves are light, radio &
TV and water waves.
2. Longitudinal Waves
•
•
•
•
Longitudinal waves are waves whose vibrations
(energy) moves in a “back and forward” motion.
We say they are ‘parallel to the wave direction’.
The only example of longitudinal waves are
“sound waves”.
(hint: long sounds like song and singing is a
sound).
2003 Qu: 18
2004 Qu: 16
2007 Qu: 28
2010 Qu: 27
(Vsound = 340 m/s)
Wave Properties
Amplitude
•
•
Is the height of a wave from the
centre to the top or the centre to
the bottom.
It has the symbol A and has the unit
of distance, m.
Wavelength
•
•
Is the length of one complete wave.
It has the symbol, λ, and also has
the unit of distance, m.
Frequency
•
•
•
•
•
Is the number of waves produced in a
unit of time, usually one second.
It has the symbol, f, and is measured in
Hertz, Hz.
It can be found by dividing number of
waves by the unit of time.
Eg 120 waves pass a point in one minute,
what is the frequency?
f = 120 / 60 = 2 Hz
Period
•
•
Is the time taken for one complete
wave to pass a certain point.
It has the symbol T, and is
measured in seconds, s.
Period & frequency
•
•
•
Period, T (s), and frequency, f (Hz)
are related by the following
equation:
T=
1
re-arranged f = 1
f
T
The above formula is not given in
the data book.
Example
f = 20 Hz
T =?
Example
• The diagrams shows a
side view of a water
wave in a ripple tank.
• The vibrating bar was
set at a frequency of 5
Hz:
Find values for:
(a) wavelength;
(b) amplitude;
(c) no. of waves per
second;
(d) Period
Waves Properties - Summary
Quantity
Definition
Symbol Unit
Wavelength Length of one full wave λ
m
Amplitude
Distance from centre
to top of wave
A
m
Frequency
No of waves in a unit
of time
f
Hz
Period
Time taken for one
complete wave to pass
T
s
2005 Qu: 12
2008 Qu: 12
2010 Qu: 13