NEET Study Notes for Electromagnetic waves, also known as EM Waves, are constituted by oscillating electric and magnetic fields. In Electromagnetic fields, the electric and magnetic field vectors are at right angles to each other and at right angles to the direction of propagation. 

• In NEET Physics Syllabus, Electromagnetic Waves is an important unit with a weightage of 5%. Candidates appearing in NEET 2022 can expect at least 1 question to be asked from this topic.
• Maxwell's Equations gave rise to the concept of Electromagnetic waves. Depending on the periodic change in electric and magnetic fields electromagnetic spectrums of different wavelengths are produced. In order of decreasing wavelength, the electromagnetic waves are radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-Rays, and Gamma Rays. 
• In this article, we have tried to explain the concepts of electromagnetic waves, characteristics, need for displacement current, electromagnetic spectrum. Sample Questions provided in the article will also help you gain a better understanding of the type of questions you can expect from this unit.

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NEET Study Notes: Important Topics in Electromagnetic Waves

NEET Study Notes for Displacement Current

Displacement current is defined in terms of the rate of change of the electric displacement field (D).

\(D=\varepsilon_0 E+P\)

Here, D= electric field displacement

\(\varepsilon_0\)= permittivity of free space

E= electric field intensity

P= polarization of the medium

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Need for Displacement Current

The nature of current in the capacitor is due to displacement current. Thus current leads to voltage. This property also has huge importance in electric applications, The nature of current helps the capacitor improve power factor is one of the fundamental aspects of any electric load.

Current in a capacitor

To understand, the formula for displacement current, consider a capacitor that starts charging. When the capacitor starts charging, there is no conduction of charge between the plates. However, due to the change in charge accumulation over time, above the plates, the electric field changes. This causes displacement current which can be explained by the following equation

\(I_D=\varepsilon_0 \frac{d \phi_E}{dt}\)

, where

• \(\varepsilon_0\)= absolute permittivity (or permittivity of free space) and
• \( \frac{d \phi_E}{dt}\)= rate of change of electric flux.
• \(I_D\) is the displacement current

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NEET Study Notes for Thermodynamics

NEET Study Notes for Electromagnetic Waves

According to Maxwell, accelerated charge is a source of electromagnetic radiation. In an electromagnetic wave, electric and magnetic field vectors are at right angles to each other and rat right angles to the direction of propagation

These possess the character of wave which propagates in a direction perpendicular to both of the directions of the oscillations and magnetic field

In the graph above, you can see that it consists of time-varying electric and magnetic fields that are perpendicular to each other and perpendicular to the direction of the propagation of the waves. Electromagnetic Waves are transverse in nature . The highest point of the wave is known as crest while the lowest point is known as a trough. The waves, whci travel in vacuum at a constant velocity of.

Characteristics of Electromagnetic Waves

• Electromagnetic Waves are transverse in nature. The electric and and magnetic fields are perpendicular to each other.
• Accelerated charges produce electromagnetic waves. These waves travel at a constant velocity of in a vacuum.
• All electromagnetic waves travel at the speed of light.
• Electromagnetic waves do not require a medium to travel
• The frequency of the wave remains unchanged but the wavelength changes when it travels from on emedium to another.
• Electromagnetic waves follow the law of superposition.
• The osciliating electric and magnetic fields and their magnitutudes have a constant ratio, The electric energy is equal to the magnetic energy in electromagnetic waves.

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NEET Study Notes for Electromagnetic Spectrum

Electromagnetic spectrum is a table that describes the known radiations of electromagnetic waves according to frequency or wavelength. The physical properties of electromagnetic waves are determined by their wavelength. This includes Gamma Rays, X-Rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves.

Uses of the electromagnetic spectrum

The uses of electromagnetic waves is provided below:

1. Radio Waves - These waves are used in radio and telecommunication systems. AM band is from 530 kHz to 1710 kHz. Higher frequencies upto 54 MHz are used for short waves bands. Television Waves range from 54 MHz to 890 MHz. FM Band is from 88 MHz to 108 MHz.

1. Microwaves- Due to the short wavelengths, microwaves are used in radar communication systems.

1. Infra Red waves-

• Infrared lamps are used in physiotherapy.
• Infrared photographs are used in photograph forecasting
• Infrared radiations are not absorbed by air. Thus they are used to take photographs of long-distance objects.
• The infrared absorption spectrum is used to study the molecular structure.

1. Visible Light- Visible light emitted and reflected from objects around us provides information around the world. The wavelength range of visible light is 4000 Å to 8000 Å.

1. Ultraviolet radiations-

• Used to destroy bacteria and sterilize medical instruments
• Radiations are used in the detection of forged documents and fingerprints in forensic laboratories.

1. X-Rays

• X-rays detect bone breaks and are generally used as a diagnostic tool in medicine
• Also used to study the crystal structure in solids.

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NEET Previous Year Sample MCQs for Electromagnetic Waves

Question.: Which of the following electromagnetic wave has maximum frequency?

1. Radio Waves
2. X-Rays
3. Gamma Rays
4. Visible Rays

Answer: Gamma Rays

Waves created as a result of vibrations between electric field and the magnetic field is called electromagnetic waves. These electromagnetic waves propagating through space and carrying electromagnetic radiant energy is called electromagnetic radiation. It consists of gamma rays, ultraviolet, X-Rays, infrared and microwaves. Gamma Rays with a frequency of 5×1022 to 3×1019 Hz have the highest frequency.

Question: Electromagnetic Waves are produced by

1. A static charge
2. An accelerated charge
3. A moving charge
4. Charged particles

Answer: Accelerated charge produced electromagnetic waves.

Question: In electromagnetic waves the phase difference between electric field vector and magnetic field vector is

1. zero
2. π∕2
3. π
4. π/3

Answer: zero

Question: A plane electromagnetic wave with a frequency of 25 MHz travel in free space. At a certain point, the electric field is 1.8 V/m. Calculate the magnetic field at this point.

1. 6×10-8 T
2. 0.6× 10-8 T
3. 3× 10-8 T
4. 18× 10-8 T

Answer: We know that in electromagnetic waves, electric and magnetic fields are perpendicular to each other and perpendicular to the propagation of waves.

Frequency of electromagnetic waves (f)= 25 MHz

Electric Field =1.8 V/m

Relation between electric field(E), magnetic field(B), and speed of light ( c) can be described by

B=E/c

B= 1.8

Question: The — light of nature is shown by the phenomenon of polarization.

1. Particle
2. Transverse
3. Longitudinal
4. Dual

Answer: Polarization of light refers to the phenomenon by which unpolarized light is transformed into polarized light. Since only transverse waves can be polarized, this phenomenon shows the transverse nature of light.

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NEET Study Notes for Kinematics

Question.: When light travels from one medium to another, the direction of propagation of light in the second medium changes. What is this phenomenon called?

1. Refraction
2. Reflection
3. Scattering
4. Polarization

Answer: When light travels from one medium to another, the direction of propagation of light in the second medium changes, This phenomenon is known as refraction

Question: Which of the following rays do not represent electromagnetic nature?

1. X- Rays
2. Microwave
3. α Rays
4. Radio Waves

Answer: α Rays

Alpha Rays which are also known as aloha particles contain two protons and two neutrons bound together into a particle. This is similar to that of helium - 4 nucleus. Thus it is not electromagnetic waves.

Question: The electric and magnetic fields of electromagnetic waves are:

1. Opposite Phase and parallel to each other
2. In phase and perpendicular to each other
3. In opposite phase and perpendicular to each other
4. In phase and parallel to each other

Answer: electric and magnetic fields of electromagnetic waves are in opposite phase and perpendicular to each other.

Question: What are X-Rays?

1. Stream of electron
2. Stream of uncharged particle
3. Electromagnetic radiation
4. Stream of proton

Answer: Electromagnetic radiation

Since X-Rays consist of oscillating electric and magnetic fields perpendicular to each other and in the direction of propagation of X-Rays. Therefore X Rays are basically electromagnetic radiation.