TOPIC 1 -Electromagnetic waves are produced when

TOPICS electrically charged particles oscillate or change

energy in some way.
1. Introduction to electromagnetics
2. Electrodynamics -The waves travel perpendicularly (900)to both
3. Maxwell’s equation electric and magnetic fields.
4. Properties of electromagnetic waves
5. Energy and Momentum in the
electromagnetic field

INTRODUCTION TO ELECTROMAGNETIC
WAVES
Objectives
1. Explain sources of electromagnetic radiations
i)Long wavelengths
ii)Visible light
iii)Short wavelengths
2. Analyse the detectors used in electromagnetic
radiations
3. Explain the application of electromagnetic
waves

Introduction:
Definition of electromagnetic waves
Electromagnetic waves refers to waves that do not
require any material medium for transmission
The electromagnetic spectrum
ELECTROMAGNETIC SPECTRUM It is divided into seven major regions or bands. A
band consists of a range of frequencies in the
spectrum in terms of frequencies
Electromagnetic spectrum is a continuum of all
electromagnetic waves arranged according to
Classifications of electromagnetic waves
frequency and wavelength. It includes:
according to wavelengths and frequencies
i) long wavelength
1. Ra –Radio waves
ii) Visible light
2. M – Microwaves
iii) Short wavelength
3. I – Infra red
4. L – Light waves(visible light)
a) LONG WAVELENGTHS
5. UV –Ultra Violet
These have greater wavelength but low frequencies
6. X - X -rays
and low energy.
7. G – Gamma Rays
They are the first three
Friend --- frequency
a)Radio waves
b) Micro waves
The order a above is the arrangement in terms of
c) Infra – red
Increasing frequency I.e Gamma rays has the
highest frequency while Radio waves has the least
B)VISIBLE LIGHT
frequency
This is the middle of electromagnetic spectrum that
NB – The wave with the Highest frequency
human eye can detect. This gives the reason why
(Gamma ) is the one with the least Wavelength,
this part of spectrum is known as Visible light.
while the wave with the least freaquecy(radio
waves), has the highest wavelength
c) SHORT-WAVELENGTH
These have shorter wavelength with high
frequencies and high energy
They represent the last three in the electromagnetic
spectrum.
i)Gamma rays
ii)X-rays
iii)Ultra – violet radiations

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 Properties of electromagnetic waves
Common properties

i) They do not require material medium for 3. Green light has a wavelength of 𝟓 𝒙 𝟏𝟎−𝟕
transmission Calculate the energy it emits
ii) They travel at the speed of light i.e. 3 × 108 ms-1 Sln
iii) They are transverse in Nature v=fλ
iv) They carry no charge, hence not affected by 𝑉 3.0 𝑥 108
f= =
electric or magnetic fields λ 𝟓 𝒙 𝟏𝟎−𝟕

v) They undergo reflection, refraction and = 𝟔 𝒙 𝟏𝟎𝟏𝟒Hz

diffraction. But E = hf
vi) Posses energy in different portion according to = 𝟔. 𝟔𝟑 𝒙 𝟏𝟎−𝟑𝟒 𝒙 𝟔 𝒙 𝟏𝟒
the relation 𝐸 = ℎ𝑓 = 𝟑. 𝟗𝟕𝟖 𝒙 𝟏𝟎−𝟏𝟗 J
vii) They obey the wave equation (v = λ f).
3.A radio station is transmitting at a frequency of
Note 15.42 MHz Calculate the wavelength Ans: 19.46m
h- Planks Constant (6.63 x 𝟏𝟎𝟏𝟒𝑯𝒛)
speed of light is given by c = 𝟑. 𝟎 𝒙 𝟏𝟎𝟖 𝒎/𝒔
4. An X –ray machine produces radio of wavelength
of 1.0 𝑥 10−11 m .Calculate:
Examples
1. A VHF radio transmitter broadcasts radio waves a) The frequency of the radiation 𝐴𝑛𝑠 𝟑 𝒙 𝟏𝟎𝟏𝟗𝑯𝒛
at a frequency of 30 M Hz. What is their b) Its energy content 𝑨𝒏𝒔: 𝟏. 𝟗𝟖𝟗 𝒙 𝟏𝟎−𝟏𝟒 𝑱
wavelength?
Solution Sources of electromagnetic Wave interference
v=fλ i) Ignition systems
𝑉 3.0 𝑥 108 ii) Cellular network of mobile phones
then λ = = iii)Motive/air space vehicle
𝑓 300 𝑥106
= 1.00 m. Generally we can say:
2. Calculate the frequency of a radio wave of i)Broadcasting station
wavelength 150 m. ii)Atmospheric discharge eg lighting
Solution : v = f λ iii) Air space and motive device
𝑉 3.0 𝑥 108 iv) Voltage surge etc.
f= =
𝜆 150
v) Ignition systems.
= 2M Hz
SOURCES,PRODUCTION,DECTECTION and APPLICATIONS OF ELECTROMAGNETIC WAVES

Type of wave Source/ How it is produced How it is detected Use/application

Radio waves By Oscillators Resonant circuits in radio receivers with 1. Used in radio, TV and cellular mobile
i.e Oscillation of electrical diodes and earphones communications.
circuit 2. Satellite imagery
From Stars, gases in space
Microwaves By Oscillation of charges in By RADAR 1. In microwave Oven to cook or warm
special Aerials mounted on food
dishes
2. In RADAR communication (Locating the
positions of aeroplanes and ships)
3. Communication in telephone and
computer data
Infra red -Sun -Human skin 1.Tv remote control
radiation -Fire -Photo graphic film 1.In cooking, heating and drying.
-TV remote system 2.In green houses to grow crops
3.Ware fare and burglar alarm system
Visible light -Sun -Human eye 1. Enable people and animals to see
-Burning candle -Photographic film 2. Photosynthesis in plants
-Lighting bulb -photocell 3.Used in LASER
UV-light -Sun -Photographic films In medicine- to kill bacteria, skin treatment
-Sparks -Photocell Source of Vitamin D
-Mercury vapour lamps -Fluorescent materials
-Paper lightly smeared with Vaseline
X -Rays -X –Rays tubes as a result in -Fluorescent screen 1.In medicine –To locate bone fracture or
the energy changes of an -Photographic film foreign objects (swallowed pins)
electron 2.Cancer therapy
3.Controlling pests and germs by radiation
4.Crystallogy-to detect flaws in metals
Gamma rays -Emitted by radioactive -Photographic plates 1.Medicine-for sterilising medical
substance -Radiation detectors(Geiger Muller Tube) equipment, killing cancerous growth
As a result of energy changes 2.Industries –to detect flaws in metal
in the nuclei of an atom

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 KEY TERMS and Points
1. ‘RADAR’ – Radio Detection and Ranging.
2. LASER- Light Amplification by the Stimulated
Emission of Radiation
3. Gamma rays have Higher energy, hence high
penetrating powers

MICROWAVE OVEN
Microwaves are also used for Cooking in a
microwave oven

How Microwave oven Works

Microwaves are produced by the Magnetrons at a
frequency of 2500M Hz. The waves are then
directed to a rotating metal stirrer which reflect
them to different parts of the oven.
In the oven, food is placed on a turntable, where it
absorbs the waves evenly. The waves heat up the
water and fat molecules in the food, thereby
cooking it.
The wire mesh on the door reflects the microwaves
back inside. The device is switched off before
opening the door.

Hazards of Some Electromagnetic waves

i. Excessive use of UV rays, X-rays and Gamma
rays, which carry high energy, may cause damage
to the body cells, skin burn, effects
ii. Cancer diseases may also occur

How to minimize dangers Posed by

Electromagnetic spectrum
i. Use of protective device to Shield the rays from
coming in contact with the skin
ii. Reducing the time of exposure
iii. Ensure the X-ray machine is installed in aroom
with cemented thick wall

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