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c. Name the social value associated with the phenomenon?
6. Charu’s father got her a new scooter. She was very happy to drive the
scooter. One day she observed that there is a speedometer in the scooter, which
gives the instantaneous speed of the scooter. Charu asked her father as to how the
speedometer able to measure the speed. Her father knew nothing about the
mechanism of measurement of speed. He went to the scooter agency to understand
the same. The manager of scooter agency called a scooter mechanic who explained
the working of speedometer. Charu’s father explained came home and explained
everything to her. Charu thanked her father for taking interest in her curiosity
a)What according to you, are the values displayed by Charu’s father?
b)Explain the working of speedometer.
7. A school proposed to organize a science exhibition. Teacher assigned a
project to Ravita to demonstrate the induced e,m.f due to change in magnetic flux.
Ravita told her friend savita that she would be unable to complete the project as her
mother is not feeling well. Savita told Ravita that she would help her to complete
the project .Ravita completed her project of flying disc with the help of Savita
.The magnitude flux in the experimental setup changes from
6x 10-3 wb to 3x10-2wb in 0.01s.Now answer the following question:
i)what values are displayed by Savita?
Ii)What is the induced e.m.f in the disc?
ELECTRO MAGNETIC WAVES
GIST
Conduction current and displacement current together have the property of
continuity.Conduction current & displacement current are precisely the same.
Conduction current arises due to flow of electrons in the conductor.
Displacement current arises due to electric flux changing with time.
Displacement current: 𝐼𝐷 = 𝜀0 ∫𝑑∅𝐸
𝑑𝑡
Maxwell’s equations:
Gauss’s Law in Electrostatics: ∮ �⃗⃗�. 𝑑𝑆⃗⃗⃗⃗⃗=𝑄
𝜖0
Gauss’s Law in Magnetism: ∮ �⃗⃗�. 𝑑𝑆⃗⃗⃗⃗⃗=0
Faraday’s -Lenz law of electromagnetic induction: ∮ �⃗⃗� . 𝑑𝑙⃗⃗⃗⃗ =− 𝑑
𝑑𝑡∮ �⃗⃗� . 𝑑𝑆⃗⃗⃗⃗⃗
Ampere’s – Maxwell law: ∮ �⃗⃗� . 𝑑𝑙⃗⃗⃗⃗ =0 I + 0 0𝑑𝜙𝐸
𝑑𝑡
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Electromagnetic Wave:-The variation of electric and magnetic fields,
perpendicular to each other, producing electromagnetic disturbance in space at
right angles to each other, which have properties of waves and propagate through
free space without any materialistic medium is called electromagnetic wave.
Properties of electromagnetic waves:
E M Waves are transverse in nature.
They are produced by oscillating or accelerating charged particles.
They do not require any medium for their propagation.
They obey principle of superposition.
They show polarization effect.
Electric field is only responsible for optical effects of EM waves.
The amplitude of electric & magnetic fields are related by 𝐸
𝐵= 𝑐
In free space they travel with the speed 𝑐 = 1
√𝜖𝑜𝜇𝑜.
The energy of E M Wave is equally divided between electric and magnetic
field vectors.
EM waves also carry energy, momentum and information.
Electromagnetic Spectrum: The orderly arrangement of electro
magnetic radiation according to its frequency or wavelength is called
electromagnetic spectrum.
ELECTRO MAGNETIC SPECTRUM, ITS PRODUCTION, DETECTION
AND USES IN GENERAL
Type
Wave length
Range
Frequency
Range
Production Detection Uses
Radio
>0.1m
109 to 105Hz
Rapid acceleration /
deceleration of
electrons in aerials
Receiver’s
aerials
Radio, TV
Communication
Micro-
wave
0.1mm
1011 to109 Hz
Klystron valve or
magnetron valve
Point contact
diodes
Radar, TV communication
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Infrared
1mm to
700nm
1011 to1014 Hz
Vibration of atom
or molecules
Thermopiles,
Bolometer
Infrared
Photographic
Film
Green House effect,
looking through haze, fog
and mist, Ariel mapping.
Light
700nm to
400nm
8x1014 Hz
Electron in an atom
during transition
Eye, Photocell,
Photographic
Film
Photography,
Illuminations, Emit &
reflect by the objects.
Ultra-
violet
400nm to 1nm
5x1014 to
8x1014
Inner Shell electron
in atom moving
from one energy
level to a lower
energy level
Photocell &
photographic
film
Preservation of food
items, Detection of
invisible writing, finger
print in forensic
laboratory. Determination
of Structure of molecules
& atoms.
X-rays
1nm to 10-3nm
1016 to 1021
Hz
X-ray tube or inner
shell Electrons
Photographic
film, Geiger
tube, ionization
chamber.
Study of crystal structure
& atom, fracture of bones.
Gamma
ray
<10-3nm
1018 to 1022
Hz
Radioactive decay
of the nucleus
Photographic
film, Geiger
tube, ionization
chamber
Nuclear reaction &
structure of atoms &
Nuclei.
To destroy cancer cells.
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CONCEPT MAP
Electromagnetic Waves
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QUESTIONS
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VALUE BASED QUESTIONS
1. A fluorescent tube seller boasts of the quality of his fittings. He offers
cheaper fittings with beautiful choke fitted on it. The customer installs it and finds
the tube working fine but giving strong humming sound . He and his wife found
the hum to be tolerable but their young children said that it is too high to be
tolerated. What do you think about the cause of hum? Comment on the character of
the seller.
2. Clinical microscopes are used to diagnose diseases based on blood and
urine samples. Mr. Bajaj does not believe in such tests. He prefers to go to doctors
who diagnose on the basis of pulse check only. He fell ill and his temperature
persisted for more than a month. Anurag a student of class twelfth resides near Mr.
Bajaj house, convinced Mr. Bajaj and got his examination conducted. How X ray
are produced? What are the values exhibited by Anurag?
3. Sushma’s mother suffers from cancer of third stage. She has been advised a
therapy in which cancerous growth will be burnt by atomic radiations. She is told
that her beautiful hair will fall in this therapy and she is liable to become bald.
Sushma’s mother refuses the therapy which is otherwise must for her. Sushma
talked to her mother explaining the need of the therapy and could convince her.
What are the values exhibited by Sushma? Which electromagnetic radiation is used
in cancer treatment?
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