1. Electromagnetic
Spectrum

2. Instructions
• Duration of Lesson: 60 Min
• Read through this powerpoint presentation
and attempt the EM wave quiz
• You can also find this chapter in your
textbook, chapter :
The grades of the quiz will be taken into you CA for semester
2, and you can only do it ONCE, so please make sure you
understand the content of this unit.

3. Introduction
Objectives:
At the end of the lesson, you will be able to
• Describe the main components of the
electromagnetic spectrum.
• State the properties of ALL EM waves.
• Discuss the role of the respective EM waves
and some of their applications.

4. What are Electromagnetic
Waves ?
• If you have ever tuned in to listen to a radio,
spoken on a handphone, turned on a light, had
an X-ray taken, felt the warmth of sun on your
skin.
• You have experienced electromagnetic wave

5. Electromagnetic wave
Electric field
Produced by Simultaneous vibration
Magnetic field
Electric field
Magnetic field
http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=52

6. Wavelength of Electromagnetic Waves

7. Hence this is the complete EM wave spectrum (the waves below
in  ascending order of wavelength;
descending order of frequency )
Gamma x-rays Ultra-violet Visible Infra- Microwave Radio wave
rays ray light red ray
Highest f Lowest f
Shortest λ Longest λ

8. Properties of EM Wave
1. All electromagnetic waves are transverse
wave

9. 2. They do not require any medium to travel
through (recall: Radiation Infra red is an EM Wave)
3. They travel at the speed of 3x108 ms-1 in
vacuum (recall: speed of light  light is also an EM Wave)

10. 4. They can all be reflected or refracted

11. 5. They can all be emitted or absorbed by
matter

12. 6. They all obey the wave equation
v =f x λ
Where v = speed of wave (m/s)
f = frequency of wave (Hz)
λ = wavelength (m)

13. 7. Their frequencies do not change as
they pass from one medium to
another. However, both their speed
and wavelength will change.
v =f x λ

14. 8. They carry energy frm one place to another
9. They are all of
neutral charge as all
of them oscillate
with electric and
magnetic field
perpendicular to
each other.

15. Overview of EM waves
Waves
Longitudinal Waves Transverse Waves
Sound waves
Electromagnetic Waves
Classified into
Properties
Comprises of
Electromagnetic Spectrum
Radiowave Infra-Red Ultra-Violet Gamma ray
Microwave Light X-ray
Applications

16. Gamma rays
Gamma rays have the shortest
wavelengths and highest
frequencies in the EM spectrum.
It is generated by :
Changes in energy levels in the nucleus
Some radioactive substances and certain
nuclear reactions produce gamma rays.
Because of their great penetrating ability,
gamma rays can cause serious illness.
However when used in controlled
conditions, gamma rays is useful in cancer
treatment.

17. X-rays
X

18. Both Gamma rays and X- rays can be
detected by:
a) photographic plates
b) ionization chamber
c) phosphorescence

19. Ultra-violet
The main source of ultra-violet radiation is sunlight and it is this
radiation which gives rise to suntan and also sunburn.
Ultra-violet radiation is used in hospitals to sterilize the surgical
instruments and operating theatres as it kills bacteria and viruses.
UV can be detected by:
a) Photographic plates
b) Photoelectric cell
c) Fluorescence

20. Visible Light
Visible light is the part of the EM
spectrum which can be detected by the
human eye.
The visible light has its own spectrum
which consist of the 7 colours of light :
Red Orange Yellow Green Blue Indigo
Violet
An example of visible light is the
colourful laser light or the light from a
firework.
Some of the uses of light is in
optical fibres in medicine and
telecommunications.

21. Infra-red waves
Heat can be transferred through infrared
radiation.
We often think of infra red as being the same
thing as 'heat', because it makes our skin feel
warm.
Most of you might have seen infra-red waves in use
during the SARS period. (picture on the top right hand
corner). It shows a thermo-detector which is placed
outside hospitals/airport to identify the warm and cool
parts of a person by analyzing infra-red radiation
emitted from the person’s body. And through this we
can see if someone is having a fever.
Infra red is useful for:
- For navigation through fog & haze as it is less
easily scattered compared to visible light
- Medical treatment : to warm injured muscles/sports
injuries

22. Microwaves
One of their most common uses is in
microwave ovens. When you switch on
a microwave oven , it gives off
electromagnetic waves that bounce
around inside the oven, penetrating the
food. Water molecules in the food
absorb the energy from the microwaves,
causing the food to get hot.
Other uses of microwaves:
a) Radar communication (as it is not easily
blocked of by buildings/trees)
b) Analysis of fine details of molecular and
atomic structure
c) Useful demonstration of all wave
properties on macroscopic scale
d) Telephone communication (mobile
phones, etc)

23. Radio waves
Radio waves are the electromagnetic waves
with the longest wavelengths and lowest
frequencies
Like all electromagnetic waves, radio waves
can travel through a vacuum. However
most of the radio waves we receive have
traveled through air. Take the radio as an
example. The radio converts the
electromagnetic waves into the sound
that comes out of the radio speakers.
Uses of radio waves:
a) Radio and television communication
(to transmit sound and picture
information over long distance)
b) Radar & satellite communication
c) Navigation or ships & aircrafts

24. Waves
Longitudinal Waves Transverse Waves
Sound waves
Electromagnetic Waves
Classified into
Properties
Comprises of
Electromagnetic Spectrum
Radiowave Infra-Red Ultra-Violet Gamma ray
Microwave Light X-ray
Applications

25. Some tips to help you to remember:
• EM Spectrum
Raja’s Mother Is Visiting Uncle Xavier’s Garden
Radio Micro Infra-red Visible Ultra-violet X-rays Gamma
wave wave Rays light ray rays
• Visible Light Spectrum
Run Off You Girls Boys In View
red orange yellow green blue indigo violet

26. Congratulations!
You’ve completed the
ELECTROMAGNETIC WAVES lesson
Please take the quiz when you’re
ready !
(Remember the Quiz will be closed by Friday, 7 Sept,
23.59PM)
See you soon in Physics Class!