CHAPTER
27
LIGHT & OTHER
ELECTROMAGNETIC
WAVES
Electromagnetic Waves:
Transverse waves produced
by the motion of
electrically charged
particles.
The electric field and
magnetic field waves at
right angles to each other.
Electromagnetic Waves:
These waves vary
depending on frequency
and wavelength.
No medium required to
travel.
Electromagnetic Waves:
Speed varies with the change
in medium.
All electromagnetic waves
travel at the same speed
8
through a vacuum (3 x 10
m/s). Their wavelength and
frequency are different.
Electromagnetic Waves:
They carry energy and
have momentum.
They have both wave and
particle like behavior.
FREQUENCY
INCREASES
RADIO WAVES
MICROWAVES
INFRARED
WAVELENGTH
DECREASES
VISIBLE LIGHT
ULTRA VIOLET LIGHT
ENERGY
X-RAYS
INCREASES
GAMMA RAYS
LIGHT
 Light is composed of
tiny “particles”.
 These particle-like
bundles of radiation
are called photons.
LIGHT
 Higher
the frequency of
the electromagnetic
waves, the greater the
energy of the wave.
 Light produces
interference patterns
like water waves.
RADIO WAVES
Have low frequency
and long wavelengths.
They have the lowest
photon energy.
RADIO WAVES
Radio waves are used to
transmit radio and TV signals.
They are also used in cellular
phones and cordless phones.
RADIO WAVES
The process of varying
radio waves is called
modulation.
Voice, light images,
computer information, and
music can be used
for modulation.
OTHER USES OF RADIO
WAVES
1. Communications
2. Navigation and defense
equipment
3.Weather Forecasting
4.TV signals
5. AM and FM radio signals
6. Airport air traffic controllers
7. Radar used by police cars
INFRA RED RADIATION
Has a wavelength slightly
longer than visible light.
Your skin feels warm
outside because your
skin is absorbing
infrared radiation
from the sun.
 A thermogram is produced
by measuring the infrared
radiation given off by
different parts of the body.
 Tumors are detected by
thermograms because they
are warmer than other parts
of the body.
Some security systems
are designed to detect
objects giving off infra
red radiation and to
respond by activating
an alarm.
Infrared radiation
are used to warm
and dry objects.
Infra red lamps in
some restaurants
keep the food
warm until served.
 Infrared images obtained
from sensors on airplanes
can yield important
information on the health
of crops and help us see
forest fires even
enveloped in an
opaque layer of
smoke.
Increasing Wavelength
Decreasing Frequency
VISIBLE LIGHT
VISIBLE LIGHT
It is the only part of the
electromagnetic spectrum
that we can see.
Violet Color has a smaller
wavelength than red
color.
ULTRA VIOLET RADIATION
They have higher frequency
than visible light.
Exposure to UV radiation
enables skin cell to
manufacture vitamin D,
which is needed for healthy
bones and teeth.
ULTRA VIOLET RADIATION
Ultra violet lamps are
used in hospitals to kill
bacteria and viruses, and
to sterilize surgical
instruments.
ULTRA VIOLET RADIATION
UV rays are used to kill
microorganisms in food and on
hospital equipment.
Some minerals like fluorite and
scheelite become fluorescent
when exposed to UV light.
Fluorescence occurs when a
material absorbs UV radiation
and re-emits visible light.
EXCESS OF ULTRA VIOLET
RADIATION
• Lead to sagging, dry skin
and even skin cancer.
Sunscreen contains
chemicals that absorb UV
radiation before they
penetrate your skin.
Crest
Ozone is found in the
Earth’s outer
atmosphere and it
protects us from most
of the sun’s UV
radiation.
Ozone is produced
naturally through
photochemical reactions
and electric discharge
reactions (lightning) in
the atmosphere.
Ozone depletion is caused
by chemicals (CFC) that
break down ozone. These
chemicals are found in
hair sprays, refrigerants
etc.
X-RAYS
X-rays have shorter
wavelength and
higher frequency
than UV radiation.
They possess enough
energy to penetrate
dense objects like skin
and muscles.
X-RAYS
When X-rays hit more
dense objects they are
absorbed.
X-rays are used to scan
luggage and packages
without opening
them at the
airport.
GAMMA RAYS
Have the highest
frequency and are the
most penetrating.
Gamma rays are
emitted
from the nuclei of
radioactive atoms.
GAMMA RAYS
Earth receives some
gamma rays from space.
They can be used to kill
cancerous cells.
GAMMA RAYS
People using gamma
radiation for treatment
suffer side affects like
nausea, hair loss, and
fatigue because healthy
cells are also damaged.