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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



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.



CONCEPT MAP

Electromagnetic Waves



QUESTIONS



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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