EM Waves 2 Flashcards
infrared radiation/heat waves
i)freq
ii)wavelength
iii)production
iv) detection
i) 3 x 10¹¹ - 4 x10¹⁴ Hz
ii)1mm to 700 nm
iii) Vibration of atoms and molecules due to heating.
iv) Thermopiles, Bolometer, Infrared
photographic film
why are IR waves valled heat waves
Infrared waves are sometimes referred to as heat waves. This
is because water molecules present in most materials readily absorb
infrared waves (many other molecules, for example, CO2
, NH3
, also absorb
infrared waves). After absorption, their thermal motion increases, that is,
they heat up and heat their surroundings.
importance of IR maintaining earth temperature
Infrared radiation also plays an important role in
maintaining the earth’s warmth or average temperature through the
greenhouse effect. Incoming visible light (which passes relatively easily
through the atmosphere) is absorbed by the earth’s surface and reradiated as infrared (longer wavelength) radiations. This radiation is
trapped by greenhouse gases such as carbon dioxide and water vapour.
uses of infrared radiations
-Infrared lamps are used in physical therapy.
- Infrared detectors are used in Earth satellites, both for military purposes and to observe growth of crops.
-Electronic devices (for example semiconductor light emitting diodes) also emit infrared and are widely used in the remote switches of household electronic systems such as TV
sets, video recorders and hi-fi systems.
visible light
i) wavelength
ii)freq
iii)production
iv)detection
It runs from about
4 × 1014 Hz to about 7 × 1014 Hz or a wavelength range of about 700 –
400 nm.
iii)Electrons in atoms emit
light when they move from
one energy level to a
lower energy level
iv) Photographic film,Photocells,The eye
use of visible light
Visible light emitted or reflected from objects around us provides
us information about the world. Our eyes are sensitive to this range of
wavelengths.
Different animals are sensitive to different range of wavelengths. For example, snakes can detect infrared waves, and the
‘visible’ range of many insects extends well into the utraviolet.
UV rays
i)freq
ii)wavelength
iii)production
iv)detection
i)7 x 10¹⁴ - 5 x 10¹⁷ Hz
ii) 400nm to 0.6nm
iii) Inner shell electrons in atoms moving from one energy level to a lower level
Ultraviolet (UV) radiation is produced by special
lamps and very hot bodies. The sun is an important source of ultraviolet
light.
iv)Photographic film,Photocells
ozone layer
The sun is an important source of ultraviolet
light. But fortunately, most of it is absorbed in the ozone layer in the
atmosphere at an altitude of about 40 – 50 km.
Ozone layer in the atmosphere plays a protective role, and hence its
depletion by chlorofluorocarbons (CFCs) gas (such as freon) is a matter
of international concern.
harmful effects of ozone layer
Exposure to UV radiation induces the
production of more melanin, causing tanning of the skin. UV radiation is
absorbed by ordinary glass. Hence, one cannot get tanned or sunburn
through glass windows.
Welders wear special glass goggles or face masks with glass windows
to protect their eyes from large amount of UV produced by welding arcs
uses of UV
Due to its shorter wavelengths, UV radiations can be focussed into very
narrow beams for high precision applications such as LASIK (Laserassisted in situ keratomileusis) eye surgery. UV lamps are used to kill
germs in water purifiers.
X rays
i)freq
ii) wavelength
iii)production
iv)detection
i) 3 x 10¹⁷ - 5 x 10²⁰ Hz
ii)1nm to 10–3 nm
iii)One common way to generate X-rays is to bombard a metal target by high energy electrons.
iv)Photographic film
Geiger tubes
Ionisation chamber
applications of x rays
X-rays are used as a diagnostic tool in
medicine and as a treatment for certain forms of cancer. Because X-rays
damage or destroy living tissues and organisms, care must be taken to
avoid unnecessary or over exposure.
gamma rays
i)freq
ii)wavelength
iii)production
iv)applications
i) 3 x10¹⁸-3 x10²² Hz
ii) 10–10m to less than 10–14m ( less than 10-3nm)
iii)This high frequency radiation is produced in nuclear reactions and also emitted by radioactive nuclei.
iv)They are used in medicine to destroy
cancer cells
