NCERT Exemplar Class 12 Physics Solutions Chapter 8 Electromagnetic Waves
NCERT Exemplar Class 12 Physics solutions chapter 8 deals with the concept of accelerating charge which produces electric field as well as magnetic field which collectively form electromagnetic waves. Stationary charges have only electric fields associated with it whereas charges moving with a constant velocity have both electric and magnetic fields associated with it. NCERT Exemplar Class 12 Physics chapter 8 solutions explains different types of electromagnetic waves and their application. .Class 12 Physics NCERT exemplar solutions chapter 8 also exhibits electromagnetic waves as a transverse wave and gives information about Maxwell’s equations of (unification of electricity and magnetism) electromagnetism.
Also check - NCERT Solutions for Class 12 Physics
NCERT Exemplar solutions for Class 12 Physics chapter 8 are very useful and detailed from the point of view of board exams as well as competitive exams like NEET and JEE Main. NCERT Exemplar Class 12 Physics solutions chapter 8 PDF download is also available, prepared by experts after thorough study.
Also see - NCERT Solutions for Class 12 Other Subjects
Question:3
Light with an energy flux of 20 wb/cm2 falls on a non-reflecting surface at normal incidence. If the surface has an area of 30 cm2, the total momentum delivered for 30 minutes is
A. 108 × 104 kg m/s
B. 36 × 10-5 kg m/s
C. 1.08 × 107 kg m/s
D. 36 × 10-4 kg m/s
Answer:
Answer: The answer is the option (d)
Solution:
U = Energy falls on the surface in that time
Momentum of the incident light
As the momentum of the reflected light is zero, then momentum of the delivered light is
Question:3
Answer:
Question:7
An EM wave radiates outwards from a dipole antenna, with as the amplitude of its electric field vector. The electric field E0 which transports significant energy from the source falls off as
a.
b.
c.
d. remains constant
Answer:
A diode antenna radiates the electromagnetic waves outwards. The amplitude of electric field vector falls intensity inversely as the distance (r) from the antenna
The answer is the option (b) 1/r
Question:8
An electromagnetic wave travels in vacuum along z-direction:
.
Choose the correct options from the following:
a) the associated magnetic field is given as
b) the associated magnetic field is given as
c. the given electromagnetic waves is plane polarised
d. the given electromagnetic field is circularly polarised
Answer:
The correct answers are the options a), b), and d).Question:9
An electromagnetic wave travelling along the z-axis is given as: . Choose the correct options from the following
(a)
(b)
(c) the associated magnetic field is given as
(d) the electromagnetic field can be written in terms of the associated magnetic field as
Answer:
Answer: The correct answers are the options (b, c and d)The direction of propagation of an electromagnetic wave is always along the direction of vector product
(a)
![]() |
(c)
(d)
Question:10
A plane electromagnetic wave propagating along x-direction can have the following pairs of E and B
a) Bx, Ey
b) Ex, By
c) Ey, Bz
d) Ez, By
Answer:
Answer: The correct answers are the options,c) Ey, Bz
d) Ez, By
Solution: The direction of propagation of electromagnetic waves is perpendicular with the magnetic field vector(B) and also with the electric field vector(E). Therefore, the electromagnetic wave that is propagating along the x-direction, will have electric and magnetic field vectors either in Y-direction or 2-direction.
Question:11
A charged particle oscillates about its mean equilibrium position with a frequency of 109 Hz. The electromagnetic waves produced:
a) fall in the region of radio waves
b) will have a wavelength of 0.3 m
c) will have a frequency of 109 Hz
d) will have a frequency of 2 × 109 Hz
Answer:
Answer: The correct answers are the options,a. fall in the region of radio waves
b. will have a wavelength of 0.3 m
C. will have a frequency of 109 Hz
Here, the particle that produces electromagnetic waves of frequency is equal to the frequency at which it oscillates about its mean equilibrium position.
So, the frequency of electromagnetic waves produced by the charged particle is v= 109 Hz.
Wavelength
The 109 Hz frequency falls under the radio wave region.
Question:12
The source of electromagnetic waves can be a charge
a) at rest
b) moving with a constant velocity
c) falling in an electric field
d) moving in a circular orbit
Answer:
Answer: The correct answers are the options,c) falling in an electric field
d) moving in a circular orbit
Question:13
An EM wave of intensity I falls on a surface kept in vacuum and exerts radiation pressure p on it. Which of the following are true?
a) radiation pressure is I/c if the wave is totally reflected
b) radiation pressure is I/c if the wave is totally absorbed
c) radiation pressure is in the range I/c < p < 2I/c for real surface
d) radiation pressure is 2I/c if the wave is totally reflected
Answer:
Answer: The correct answers are the options,a) radiation pressure is I/c if the wave is totally absorbed
c) radiation pressure is in the range I/c < p < 2I/c for real surface
d) radiation pressure is 2I/c if the wave is totally reflected
Question:14
Why is the orientation of the portable radio with respect to broadcasting stations important?
Answer:
We know that the electromagnetic waves are plane-polarized. Therefore, the antennas are to be placed in parallel to the vibration of the electric or magnetic field of the wave. That is why the orientation of the portable radio with respect to the broadcasting station is important.Question:15
Why does a microwave oven heat up a food item containing water molecules most efficiently?
Answer:
The frequency of the microwave is exactly the same as that of the resonant frequency of the water molecules in a food item. That is why, the microwave oven heats up a food item containing water molecules most efficiently.Question:16
Answer:
Here, the value of displacement current through the capacitor is Id
Therefore,
Given,
Substituting the values in the equation a), we get
Question:18
Answer:
Here, given equation,
Standard equation,
By comparing the given equation with the standard equation, we get:
Question:19
Answer:
In an electromagnetic waves, LetLet
Since
The variation of

Question:20
Answer:
Like other waves, the electromagnetic wave has the same properties. Therefore, an electromagnetic wave has energy and momentum. It exerts pressure called radiation pressure due to momentum.Question:22
Electromagnetic waves with wavelength
i) is used in satellite communication
ii) is used to kill germs in water purifies
iii) is used to detect leakage of oil in underground pipelines
iv) is used to improve visibility in runaways during fog and mist conditions
a) identify and name the part of the electromagnetic spectrum to which these radiations belong
b) arrange these wavelengths in ascending order of their magnitude
c) write one more application of each
Answer:
a) i)ii)
iii)
iv)
b) By arranging those wavelengths in ascending order:
c) i) Gamma rays: Those are used in nuclear structures.
ii) X rays: Those are used in medical diagnosis.
iii) UV rays: Those are used in the preservation of food.
iv) Infrared rays: Those are used to take photograph
Question:23
Show that the average value of radiant flux density S over a single period T is given by
Answer:
We know that radiant flux density is:Let, along the X-axis, electromagnetic waves are propagating. If along the Y-axis, the electric field vector of electromagnetic waves is there. In the same way, along the z-axis, magnetic field vectors will be there. Hence,
The average value of the radiant flux density is
Therefore,
Question:25
Answer:
Energy received by the surface per second,No.of photons received per second by the surface
For a perfectly absorbing surface, is
Force
,
Pressure,
Question:26
Answer:
When the distance is doubled, the intensity of light becomes one-fourth.Following are the geometrical characteristics of the LASER those missing in the case of normal light from the bulb:
a) unidirectional
b) monochromatic
c) coherent light
The above characteristics are missing in the case of light from the bulb
Question:27
Answer:
Even though an electric field E exerts a force qE on a charged particle yet the electric field of an EM wave does not contribute to the radiation pressure because radiation pressure is the result of the action of the magnetic field of the wave on the electric currents which is induced by the electric field.Question:28
Answer:
The electric field in an infinitely long thin wire isMagnetic field due to the wire is
The equivalent current flowing through the wire is
Question:30
A long straight cable of length l is placed symmetrically along the z-axis and has radius a. The cable consists of a thin wire and a coaxial conducting tube. An alternating current flows down the central thin wire and returns along the coaxial conducting tube. The induced electric field at a distance s from the wire inside the cable is
In
a) calculate the displacement current density inside the cable
b) integrate the displacement current density across the cross-section of the cable to find the total displacement current I
c) compare the conduction current with the displacement current
Answer:
a) The displacement current density is given asb) Total displacement current
c) The displacement current is
Question:31
A plane EM wave travelling in vacuum along z-direction is given by
a) evaluate over the rectangular loop 1234 shown in the figure
b) evaluate over the surface bounded by loop 1234
c) use equation to prove
d) by using a similar process and the equation prove that
Answer:
a)b)
c) Substituting the above equations in the following equation we get
d)
We get
Question:32
A plane EM wave travelling along z-direction is described by show that,
i) the average energy density of the wave is given by
ii) the time - averaged intensity of the wave is given by
Answer:
i) The energy density due to electric field E isThe energy density due to magnetic field B is
The average energy density of the wave is given by :
ii)
Assuming
We know that
The time -averaged intensity of the wave is given as
Main Subtopics of NCERT Exemplar Class 12 Physics Solutions Chapter 8 Electromagnetic Waves
- Introduction
- Displacement Current
- Electromagnetic Waves
- Sources of electromagnetic waves
- Nature of electromagnetic waves
- Electromagnetic Spectrum
- Radio waves
- Microwaves
- Infrared waves
- Visible rays
- Ultraviolet rays
- X-rays
- Gamma rays
What will the Students learn from NCERT Exemplar Class 12 Physics Solutions Chapter 8?
From Class 12 Physics NCERT Exemplar solutions chapter 8, the students will be able to learn a lot about various properties, and facts of different kinds of rays present in the electromagnetic spectrum and how they are used differently in different places and situations. They will also get an insight into application of these concepts in various daily activities, and also about how the electromagnetic waves work in real life to provide various facilities such as the process of carrying of radio and TV signals from broadcasting stations, how such waves are used for these purposes, how light carries energy from sun to earth and much more. From NCERT Exemplar Solutions For Class 12 Physics chapter 8, the learners will also be able to verify the nature of electromagnetic waves as polarised light with its use in transfer of Radio and TV signals which place the antenna at a desired alignment, and in a particular direction to catch the signals from broadcasting stations.
NCERT Exemplar Class 12 Physics Chapter Wise Links
Important Topics To Cover For Exams From NCERT Class 12 Physics Chapter 8 Electromagnetic Waves
· NCERT Exemplar Class 12 Physics solutions chapter 8 also discuss the nature and source of electromagnetic field and defines electric and magnetic field vector which vibrate perpendicular to each other i.e. the electric field along x-axis, and magnetic field along y-axis and also shows the direction of which can travel through vacuum wave propagation perpendicular to both fields i.e. along the z-axis.
· The electromagnetic waves is featured with a variety of qualities explained in NCERT Exemplar solutions for Class 12 Physics chapter 8 along with various phenomena attached to it such as the radiation pressure, the energy and momentum carrier along with formula to calculate the amount of energy transported by such waves on any surface with the help of pointing vector.
· NCERT Exemplar Class 12 Physics solutions chapter 8 also includes questions related to the electromagnetic spectrum containing different kinds of waves such as UV rays, Gamma rays, X-rays, Infrared rays, etc. having different frequencies and wavelengths.
NCERT Exemplar Class 12 Solutions
Also, check the NCERT solutions of questions given in book
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- NCERT Solution for Class 12 Physics
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- NCERT Solution for Class 12 Maths
- NCERT Solution for Class 12 Biology
Must read NCERT Notes subject wise
- NCERT Notes for Class 12 Physics
- NCERT Notes for Class 12 Chemistry
- NCERT Notes for Class 12 Maths
- NCERT Notes for Class 12 Biology
Also Check NCERT Books and NCERT Syllabus here:
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- NCERT Syllabus Class 12 Physics
- NCERT Books Class 12
- NCERT Syllabus Class 12
Frequently Asked Question (FAQs) - NCERT Exemplar Class 12 Physics Solutions Chapter 8 Electromagnetic Waves
Question: Are these questions as per the marking scheme of CBSE?
Answer:
Yes, each and every question and Class 12 Physics NCERT Exemplar solutions chapter 8 is solved in a way that is deemed fit by CBSE involving each step and diagram that gets separate marks.
Question: Are these questions helpful in entrance exams?
Answer:
Yes, these questions and NCERT Exemplar Class 12 Physics solutions chapter 8 are highly useful in preparation of the entrance exams of both engineering and medical science.
Question: What all things one will learn from this chapter?
Answer:
One will learn all the basics of the electromagnetic waves and their properties like radio waves, microwaves, IR rays, UV rays, gamma rays etc.
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