1
Q
Radiowaves
A
- Radio waves are produced by the accelerated motion of charges in conducting
wires. - They are used in radio and television communication systems.
- They
are generally in the frequency range from 500 kHz to about 1000 MHz. - The AM (amplitude modulated) band is from 530 kHz to 1710 kHz. Higher frequencies upto 54 MHz are used for short wave bands.
- TV waves range
from 54 MHz to 890 MHz. - The FM (frequency modulated) radio band extends from 88 MHz to 108 MHz.
- Cellular phones use radio waves to transmit voice communication in the ultrahigh frequency (UHF) band.
2
Q
Microwaves
A
- Microwaves (short-wavelength radio waves), with frequencies in the gigahertz (GHz) range, are produced by special vacuum tubes (called klystrons, magnetrons and Gunn diodes).
- Due to their short wavelengths,
they are suitable for the radar systems used in aircraft navigation.
-
3
Q
Visible light
A
- It is the part of the
spectrum that is detected by the human eye. - It runs from about
4 × 1014 Hz to about 7 × 1014
Hz or a wavelength range of about 700
400 nm. - Visible light emitted or reflected from objects around us provides
us information about the world. - Our eyes are sensitive to this range of
wavelengths.
4
Q
X- Rays
A
- It
covers wavelengths from about 10–8 m (10 nm) down to 10–13 m
(10–4 nm). - One common way to generate X-rays is to bombard a metal
target by high energy electrons. - 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.
5
Q
gamma rays
A
- They lie in the upper frequency range of the electromagnetic spectrum
and have wavelengths of from about 10–10m to less than 10–14m. - This
high frequency radiation is produced in nuclear reactions and
also emitted by radioactive nuclei. They are used in medicine to destroy
cancer cells.
6
Q
Infrared waves
A
- Infrared waves are produced by hot bodies and molecules.
- This band
lies adjacent to the low-frequency or long-wave length end of the visible
spectrum. - 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). - 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.
7
Q
how do infrared rays help in mainatining the temperature of the earth
A
- 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 re-radiated as infrared (longer wavelength) radiations. - This radiation is
trapped by greenhouse gases such as carbon dioxide and water vapour.
8
Q
UV rays
A
- wavelengths ranging from about 4 × 10–7 m (400 nm) down to
6 × 10–10m (0.6 nm). - Ultraviolet (UV) radiation is produced by special
lamps and very hot bodies. 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. - 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. - Due to its shorter wavelengths, UV radiations can be focussed into very
narrow beams for high precision applications such as LASIK (Laser
assisted in situ keratomileusis) eye surgery. - 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.
physics
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