Transcript (UV) radiation? - Sackville School

M. Manser (2014)
Module P1:

EM waves

UV, skin cancer and sunburn

CFCs and the ozone layer
M. Manser
Sackville School
Name, in order of frequency or wavelength, the seven parts of the
electromagnetic spectrum.
Explain the effect of skin pigment on the risk of cancer
Calculate how long a person may safely spend in the sun using SPF
Describe how the ozone layer protects the Earth from ultraviolet radiation
and the damaging effect of CFCs
M. Manser
Sackville Schooll
The shorter the wavelength (and higher the frequency) of electromagnetic
waves, the more energy that they carry.
radio
waves
10 m
microwaves
10 cm
infrared
1 mm
visible
light UV
0.01 mm
100 nm
X-rays
1 nm
gamma
rays
0.01 nm
energy increases
hazard increases
High-frequency electromagnetic waves, such as gamma rays, are potentially more
harmful because they have more energy.
 absorption – The process in which electromagnetic waves
hit a surface and their energy is transferred to the material.
 electromagnetic spectrum – The continuous series of
electromagnetic waves in order of wavelength or frequency.
 frequency – The number of waves passing a point every
second, measured in hertz (Hz).
 gamma rays – Electromagnetic waves with the shortest
wavelengths. Uses include sterilizing medical equipment and
cancer treatment.
 infrared waves – Electromagnetic waves given off by hot
objects. Uses include heating, cooking and remote controls.
 microwaves – Electromagnetic waves that are shortwavelength radio waves. Uses include mobile phones, radar
and cooking.
 radio waves – Electromagnetic waves with the longest
wavelengths. Used for communications.
 reflection – The process in which electromagnetic waves
bounce back from a surface.
 wavelength – The distance between two matching points
on neighbouring waves, which is measured in metres.
 ultraviolet rays – Electromagnetic waves that can be
absorbed by certain chemicals and emitted as visible light.
Uses include tanning beds and security marking.
 visible light – Electromagnetic waves that are detected
by our eyes, allowing us to see. Other uses include optical
fibre communications and imaging.
 X-rays – Electromagnetic waves that pass through most
materials. Uses include medical imaging and security.
Ultraviolet rays and the ozone layer
Ozone
Ozone, O3 , is a form of
oxygen that is different
to O2.
Ozone is formed from
oxygen in a reversible
reaction.
Ultraviolet rays and the ozone layer
The ozone layer
The ozone layer is the part of the upper atmosphere where ozone is
found in the highest concentrations.
The ozone there absorbs
ultraviolet radiation,
preventing most of it
from reaching the
ground.
This is important
because ultraviolet
radiation can lead to skin
cancer.
Ultraviolet rays and the ozone layer
The ozone layer
Near the end of the last century, scientists discovered that ozone
levels over the Antarctic were reduced. This discovery was
unexpected. Chemists knew that reactive chlorine atoms could
destroy ozone. They also knew that chemicals called
chlorofluorocarbons - CFCs - break down in ultraviolet light to release
reactive chlorine atoms. Scientists used these ideas to explain the low
ozone levels.
CFCs were once used widely in
insulating foam and aerosol spraycans. Once released, they gradually
spread through the atmosphere,
eventually reaching the ozone layer.
Once there, they destroy ozone.
CFCs have now been almost
completely replaced by chemicals that
do not cause this damage.
Everyday we are exposed to ultraviolet (UV) radiation emitted
by the Sun.
UV radiation is high-energy electromagnetic radiation that is
found between visible light and X-rays on the electromagnetic
spectrum.
ultraviolet
infrared
10-3
10-6
gamma
X-rays
rays
10-9
wavelength of electromagnetic waves
The wavelength of UV radiation ranges from 10 to 1000 nm.
Humans cannot see UV radiation but research has shown
that bees, birds, butterflies and other insects can.
10-12
Ultraviolet radiation is emitted by very hot
objects, such as the Sun.
Electrical sparks and arc welding also
reach temperatures that are high
enough to produce ultraviolet radiation.
Some gases emit ultraviolet radiation
when an electric current is passed
through them.
Tanning beds and the ‘black lights’ seen
in night clubs use ultraviolet rays that
have been produced in this way.
Bright clothing
Certain chemicals can absorb UV radiation
and then re-emit it as visible light. Some
washing powders use these to make white
material appear whiter in sunlight. Such
chemicals are also used in safety clothing.
Security marking
Special inks, that are only visible under
UV radiation, are used to security mark
expensive items.
Tanning
UV radiation in sunlight causes skin to tan. Tanning beds
imitate sunlight by emitting artificially-produced UV rays.
Chemicals that absorb energetic ultraviolet
radiation and re-emit it as less energetic visible
light are said to be fluorescent. These chemicals
are used in inks and in safety clothing.
Fluorescent inks, that are not visible under
normal light, are used in banknote
production to prevent fraud. The inks
identify genuine banknotes by glowing
brightly under ultraviolet light.
Fluorescent inks are also used in stamps to
distinguish different values for automatic
sorting.
The skin uses UV radiation from the Sun to make vitamin D, which is needed for
strong bones. Some exposure to UV radiation is beneficial but overexposure is
generally harmful to the skin and eyes.
Ultraviolet radiation can damage cells.
Sunburn occurs when the skin is exposed to
high-intensity ultraviolet radiation, which
damages and kills skin cells.
Over time, repeated exposure leads to
premature ageing of the skin and increases the
risk of skin cancer.
Intense UV radiation can inflame the eyes and long-term
exposure may cause cataracts.
Some people think that a suntan is safe and makes them look healthy.
In fact, a suntan is a sign of skin that has been damaged by UV radiation. It is the
skin’s attempt to protect cells from further damage by creating its own sunscreen.
The pigment MELANIN is produced which then protects the layers below.
A suntan only provides some protection and naturally dark or tanned skin can still
suffer sunburn.
Not all skin types are able to tan. This is why fair skin and skin that is easily
sunburnt is most at risk from UV damage.
People with dark skin naturally have more
MELANIN pigment in their skin.
Everyone, regardless of skin type, is at risk from
eye damage caused by UV radiation.
Prolonged exposure to UV radiation carries serious health risks and so
protection is important.
A combination of measures can protect skin and
eyes from UV radiation:
Cover up, stay in the shade, wear a widebrimmed hat and sunglasses.
Sunblock and sunscreen protect the skin by blocking UV
radiation. When out in the Sun for prolonged periods,
these should be applied to the skin generously and often.
Time you can safely = SPF x the time it normally
stay in the sun
takes for your skin to burn