Transcript Light – Electromagnetic and Visible Spectrum

Light
Electromagnetic and
Visible Spectrum
Electromagnetic Waves

Consist of changing magnetic and electric
fields moving through space at the speed
of light (3.0 x 108 m/s)

Are produced by vibrating charged particles

Do not require a medium
Electromagnetic Spectrum

Range of frequencies of electromagnetic waves

As frequency increases, wavelength decreases

As frequency increases, energy of a wave
increases
Electromagnetic
Spectrum
The light we can see is only
a small part of all light.
 The whole range is called
the electromagnetic
spectrum and visible light is
in the middle of it.
 On the low energy end of
the spectrum are radio
waves. On the high energy
end are gamma rays.

E-M Spectrum
Visible
Microwaves
Radio waves
Infrared
X-rays
Ultraviolet Gamma-rays
Radio Waves

have the lowest frequency and the longest
wavelength.

includes TV waves, which are “vhf” (very high
frequency) or “uhf” (ultra high frequency), and
radar waves, with highest frequency

Each radio station broadcasts at a set frequency.

Sound waves are converted into electrical signals
and change (modulate) the carrier waves.
am - amplitude modulation
fm - frequency modulation

In receiver antennae, electrons are made to vibrate
sympathetically at set frequency (concept of
resonance)
Microwaves






Penetrate food evenly.
Match the natural frequencies of large molecules,
which vibrate and produce heat to cook food from
inside.
Air molecules in the oven are too small to be excited,
and microwaves also have no effect on ceramics,
plastic, or glass.
Metals reflect microwaves.
Droplets of water absorb microwaves and form steam.
When food is removed from an oven, molecules
continue to vibrate, so “stand” time is included in
recipes.
Infrared

Atoms and molecules vibrate to produce
infrared waves.

All objects emit infrared waves in the form
of heat.

uses for infrared waves:
Sun, fire, radiation, heat lamps used in
restaurants
Visible Light

electromagnetic radiation to which human
eyes are sensitive.

makes up less than 10-6 % of electromagnetic
spectrum

different frequencies are seen as colors.
red – lowest frequency and lowest energy
violet – highest frequency and highest energy
Ultraviolet

Overexposure can cause sunburns and skin cancer

uses: medicine to sterilize surgical instruments by
killing bacteria

higher UV frequencies are blocked by gas in
atmosphere

Fact or Fiction: Sunlight through a window can give
you a sunburn?
Fiction- Ultraviolet rays can not penetrate through a
window. It is infrared waves that are passing through
and that is why it is warm.
X-rays

discovered by Wilhelm Roentgen

produced by greatest acceleration of
electrons.

uses: x-ray machine for bodies or teeth, to
check luggage at airports
Gamma Rays

highest energy and greatest penetrating power

produced by nuclear reactions, including decay
of radioactive atoms and nuclear explosions

kills cancer cells before it kills healthy cells

uses: removing decay-causing bacteria from
many foodstuffs or preventing fruit and
vegetables from sprouting to maintain freshness
and flavor