Wave is nothing but a pattern of disturbance which propagates and carry energy with it. You can produce a wave on a rope by moving one end of the rope up and down. The wave produces on rope needs a medium to propagate and here medium is rope itself. This type of waves is known as mechanical waves. But in the case of Electromagnetic waves, they don't need a medium to propagate. Electromagnetic waves are waves that are created as a result of variations of electric field and a magnetic field. Or we can say that Electromagnetic waves are nothing but changing magnetic and electric fields. Electromagnetic waves are also known to be solutions of Maxwell's equations. And Maxwell's equations are the fundamental equations of electrodynamics. Electromagnetic waves can transmit energy and travel through a vacuum. light waves are examples of electromagnetic waves. Generally, Electromagnetic waves are shown by a sinusoidal graph.
As shown in figure Electromagnetic waves consist of time-varying electric and magnetic fields and they are perpendicular to each other And these both fields are also perpendicular to the direction of propagation of waves. And because of this Electromagnetic waves are transverse in nature.
Electromagnetic waves are one of the most important chapters from modern physics while preparing for all competitive exam because it helps you to understand the important properties of Electromagnetic waves. This chapter will also help you to understand various types of Electromagnetic waves and their applications. This is easy to understand and a high scoring topic. Sometimes the Concept of Electromagnetic waves and other chapters of physics are mixed in miscellaneous questions which are asked in various competitive exams.
Crack JEE 2021 with JEE/NEET Online Preparation Program
Start Now
So we will discuss step by step about important topics from this chapter followed by an overview of this chapter. Then we will understand important formulas from this chapter. Remembering these formulas will increase your speed while question-solving.
Electromagnetic waves and their characteristics. Transverse nature of electromagnetic waves.
Electromagnetic spectrum (microwaves, infrared, visible, radio waves, X-rays, ultraviolet, gamma rays). Applications of e.m. waves.
In Electromagnetic waves chapter, we will learn Electromagnetic waves, their all the important properties, their types, and their applications. So we will learn about
Maxwell’s Equations- As Electromagnetic waves are also solutions of Maxwell's equations. So it important to learn about them. James C. Maxwell noticed an inconsistency in Ampere’s Law and an asymmetry in the laws of electromagnetism. So he provided some suggestions in these laws. For example, he suggested the idea of Displacement current to remove this inconsistency in Ampere’s Law. Thus he provided a modified version of these laws with the help of Maxwell's equations which are given below-
Maxwell's 1st equation -Gauss's Law for electrostatics
Maxwell's 2nd equation: Gauss’s Law in Magnetism
Maxwell's 3rd equation-Faraday's law
Maxwell's 4th equation-Ampere's law
Electromagnetic waves properties-
These waves do not require a medium for propagation and they are transverse in nature.
These waves propagate through space with the speed of light in vacuum.
The wave having higher the frequency, will have the higher energy associated with it.
It can be used to carry information.
It travels in straight lines.
It can be split and recombined to form interference / Diffraction pattern.
It can be reflected or refracted.
Electromagnetic Wave Equation-
One of the very important types of electromagnetic waves is sinusoidal plane waves. All electromagnetic waves can be considered as a linear superposition of sinusoidal plane waves traveling in arbitrary directions.
For example- A plane wave traveling in the x-direction is of the form
And if E is in the y-z plane then
Where E - Electric field at (x,t)
- Electric field amplitude
= Angular frequency
c= Speed of light in vacuum
Similarly, B is in the y-z plane
Where B = Magnetic field at (x,t)
= Magnetic field amplitude
The important physical quantity of Electromagnetic waves
You will learn about some physical quantity given below-
The intensity of Electromagnetic wave
The momentum of Electromagnetic wave
The energy density of Electromagnetic wave
The wavelength of Electromagnetic Wave
Frequency of Electromagnetic wave
Depending on the range of frequency of wave there are various types of Electromagnetic wave. And these waves have various applications in our day to day life. Following are some types of Electromagnetic wave
γ - Ray (Gamma Ray)- Useful in In detecting a fault, crack, flaws, holes in metals.
X Rays- Useful in X-Ray therapy.
Ultraviolet Radiation- Helps In the study of molecular structure.
Infrared Waves- Helps for taking photographs in fog or smoke
Microwaves-These are used in radio and TV communication.
E is in the y-z plane
B is in the y-z plane
For Electromagnetic Waves, chapter concepts in NCERT are enough but you will have to practice lots of questions including previous year questions and you can follow other standard books available for competitive exam preparation like Concepts of Physics (H. C. Verma) and Understanding Physics by D. C. Pandey (Arihant Publications).
Chapters No. |
Chapters Name |
Chapter 1 |
|
Chapter 2 |
|
Chapter 3 |
|
Chapter 4 |
|
Chapter 5 |
|
Chapter 6 |
|
Chapter 7 |
|
Chapter 8 |
|
Chapter 9 |
|
Chapter 10 |
|
Chapter 11 |
|
Chapter 12 |
|
Chapter 13 |
|
Chapter 14 |
|
Chapter 16 |
|
Chapter 17 |
|
Chapter 18 |
|
Chapter 19 |
|
Chapter 20 |
|
Chapter 21 |
An EM wave from air enters a medium.The electric fields are
in air and
in medium, where the wave number k and frequency ν refer to their values in air. The medium is non-magnetic. If
and
refer to relative permittivities of air and medium respectively, which of the following options is correct ?
A plane electromagnetic wave of wavelength λ has an intensity I. It is
propagating along the positive Y-direction. The allowed expressions for the electric
and magnetic fields are given by :
A plane polarized monochromatic EM wave is traveling in vacuum along z direction such that at it is found that the electric field is zero at a spatial point
. The next zero that occurs in its neighbourhood is at
. The frequency of the electromagnetic wave is :