Chapter 2: Close
Chapter
Reading
: Electromagnetic
of Unfamiliar Text
spectrum – Oral 1
Electromagnetic spectrum
(Extension material for Level 2 Physics Study Guide, ISBN 978-1-927153-37-6, page 61)
Visible light waves form a tiny part of the family of electromagnetic waves, which also
includes radiowaves, microwaves, X-rays and gamma rays. All of these waves travel at the
same speed, the speed of light, c, in a vacuum.
c = 3.0 × 108 m s–1. The waves differ in their frequency and wavelength. The wave formula
v = f λ can still be applied to electromagnetic waves.
Example
Find the wavelength of radiowaves transmitted from an FM station with a transmitting
frequency of 98.2 MHz.
Solution:
v = f λ
3.00 × 108 = 98.2 × 106 × λ
[substituting]
6
λ = 3.0 × 106
98.2 × 0
= 3.05 metres
The electromagnetic spectrum extends infinitely in each direction. Theoretically, there
is no limit to the frequency of electromagnetic waves. They can have extremely low
frequencies or extremely high frequencies.
The range of frequencies and wavelengths for each type of electromagnetic wave is not
clearly specified and some ranges overlap.
Infrared waves are produced by hot objects and so these waves are often called radiated
heat.
Ultraviolet waves are often called ultraviolet light even though the waves are outside the
range visible to the human eye.
10 1
AM
r ad
10 5
10 6
10 7
lo n g r
a d io
wa
ve
s
10 4
io
108
106
10 –7
infrared
10 –8
let
avio
ult r
x-
10 –9
VIS
I
10 3
FM
& d io
TV r a
10 2
10 –6
w a ves
E
d io
rt ra
sh o
BL
10 –1
1
Waveleng t h, m
10 –4 10 –5
–3
10 –2 10
12
1010 10 1014
1016
Freq uen cy, Hz
104
102
10
1
ra
10 –10
ys
10 –11
1018
10 –12
1020
1022
gamma
rays
10 –13
1023
The family of electromagnetic waves is laid out according
to their frequency and corresponding wavelength.
© ESA Publications (NZ) Ltd, Customer freephone: 0800-372 266
10 –14
2 Level 2 Physics Study Guide
Electromagnetic waves get their name because they are made up of oscillating electric
and magnetic fields. These two fields are positioned at right angles to each other and
oscillate at right angles to the wave propagation direction.
electric field
magnetic field
wave
propagation
direction
The energy in an electromagnetic wave is stored in the two oscillating fields.
© ESA Publications (NZ) Ltd, Customer freephone: 0800-372 266