All about simple traveling waves

1. Topic 4 – Oscillations and Waves
4.3 Wave Characteristics

2. Waves
● A wave is an oscillation that can move energy
from place to place without the transfer of
matter.
● An oscillation moves no energy nor matter
overall.
● Waves can either be a pulse or a continuous
travelling wave.
● In most cases the oscillations of the particles
making up the wave can be considered to be
simple harmonic motion.

3. Types of waves
● Transverse waves
● The vibration of the
particles are at 90o
to the
direction of propagation of
the wave.
● These are seen as water
waves, surface
earthquake waves, and as
electromagnetic waves.
● Physical trasverse waves
cannot propagate in
gases.
● Longitudinal waves
● The vibration of the
particles is parallel to the
direction of propagation of
the wave.
● These are pressure
waves and are seen as
sound waves and
earthquakes.

4. Transverse Waves
Crest
Trough
Amplitude
Wavelength
x
r
Oscillations
Energy
Displacement

5. Longitudinal Waves
Compression
Rarefaction
Amplitude
Wavelength
y
x, r
Oscillations
Energy
Displacement

6. Intensity and Amplitude
● The intensity of a wave is the energy delivered
by it per second per unit area of detector.
● It therefore has units of Wm-2
● The intensity of a wave is directly proportional
to the amplitude of the wave squared.
I ∝ x0
2

7. Frequency and Period
● The period (T) of a wave is the time taken in
seconds for it to make one complete cycle.
● As most of the waves that we use have very
short periods we often use the frequency of the
wave instead.
● The frequency (f) of a wave is the number of
complete cycles in 1 second and is measured
in hertz (Hz).
f =
1
T

8. Wave Speed
● The speed with which a wave transfers energy
from place to place is known as the wave
speed.
● The distance a wave travels in one cycle is the
wavelength.
● The time taken for one oscillation is the time
period.
● The wave speed is therefore given by:
v=
x
t
= λ
T
=λ f

9. Waves in 2 Dimensions
● There are two distinct ways to describe the
motion of waves in 2 dimensions
● Rays – The wave is represented by an arrow which
lies in the direction of propagation.
● Wavefronts – The wave is represented by a series
of parallel lines that are perpendicular the direction
of propagation and show the position of each wave
crest or compression.
● Both of these methods have their uses in
specific situations and can sometimes be seen
used together.

10. Waves in 2 Dimensions
A series of wavefrontsA light ray Combined notation
The same wave in 2 dimensions

11. Transverse Waves in 2 Dimensions
● Sometimes, the direction of oscillation of a
transverse wave is shown on the ray.
Oscillations Up and Down
Oscillations In and Out
Oscillations both Up and Down
and In and Out

12. Electromagnetic Waves
● Electromagnetic waves rely on the oscillations
of electric and magnetic fields rather than
particles to move energy.
● In a vacuum, all electromagnetic waves travel
at the same speed, c = 3.00x108
ms-1

13. Electromagnetic Spectrum
● Electromagnetic waves can have any
frequency.
● The continuous spectrum of electromagnetic
waves goes from radio waves at low energy up
to high energy gamma waves
● Different wave bands are divided by their
wavelengths

14. The Electromagnetic Spectrum

15. Questions
● An electromagnetic wave has a frequency of
5.6x1012
Hz. What is the wavelength and
waveband of this radiation?
● High energy x-rays have a wavelength of 10pm.
What is the frequency of this radiation in a
vacuum?
● A red laser is fired in a vacuum. What is the
frequency of this radiation.
● A sound wave is measured to have a frequency
of 15kHz and a wavelength of 2.2cm. What is
the speed of this sound?