Question: Q. 3. Name the type of EM waves having a wavelength range $10^{-7} \mathrm{~m}$ to $10^{-9} \mathrm{~m}$. How are these waves generated? Write their two uses.
U [O.D. Comptt. III 2017]
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Solution:
Ans. Name of EM wave
Method of generation
1
Two uses
1
EM waves : ultra violet
1
Sun is an important source of UV rays. Some special lamps and very hot bodies also produce UV rays.
Uses :
(i) In lasik eye surgery. $1 / 2$
(ii) UV lamps are used to kill germs in water purifiers.
[CBSE Marking Scheme 2017]
Detailed Answer :
(i) Ultraviolet rays : Wavelength $10^{-8} \mathrm{~m}-10^{-6} \mathrm{~m}$, frequency $10^{17} \mathrm{~Hz}-10^{15} \mathrm{~Hz}$ (ii) Generation :
Ultraviolet rays are produced by large energy changes in electrons of an atom which occur with heavy or light elements. Sun produces large amount of ultraviolet radiation that gets absorbed by ozone layer.
(iii) Uses :
(a) Used in spectroscopy. $1 / 2$
(b) Used in mineral analysis as certain minerals exhibit strong fluorescence under ultraviolet radiation. $1 / 2$
AI Q. 4. Name the parts of the electromagnetic spectrum which is :
(i) suitable for radar systems used in aircraft navigation.
(ii) used to treat muscular strain.
(iii) used as a diagnostic tool in medicine.
Write in brief, how these waves can be produced.
R [Delhi I, II, III 2015]
Ans. (i) Microwave,
Production : Klystron/magnetron/Gunn diode
(Any one) $1 / 2$
(ii) Infrared Radiation,
Production : Hot bodies/vibrations of atoms and molecules.
(iii) $X$-Rays,
Production : Bombarding high energy electrons on metal target/ $x$-ray tube/inner shell electrons.
(Any one) $1 / 2$
OR
[Topper’s Answer 2015]
