Electromagnetic spectrum

Electromagnetic spectrum

Edited By Vishal kumar | Updated on Jul 02, 2025 07:30 PM IST

The electromagnetic spectrum encompasses all types of electromagnetic radiation, ranging from radio waves to gamma rays, each with its own wavelength and frequency. This spectrum is fundamental to numerous technologies and scientific fields. For instance, radio waves are essential for communication systems like television and mobile phones, while microwaves are used in radar and cooking. Infrared radiation is employed in remote controls and thermal imaging, whereas visible light is crucial for human vision and photography. Ultraviolet light, X-rays, and gamma rays have significant roles in medical imaging and treatments. In this article, we will discuss the concept of the Electromagnetic spectrum, and important terms related to it and provide examples for a better understanding

This Story also Contains
  1. Electromagnetic Spectrum
  2. Earth's Atmosphere
  3. Solved Examples Based on Electromagnetic Spectrum
  4. Summary
Electromagnetic spectrum
Electromagnetic spectrum

Electromagnetic Spectrum

The electromagnetic spectrum encompasses all types of electromagnetic radiation, from low-frequency radio waves to high-frequency gamma rays. This spectrum is essential for various technologies and scientific fields. Radio waves enable communication systems like radio, television, and mobile phones, while microwaves are used in radar and cooking. Infrared radiation is employed in remote controls and thermal imaging, whereas visible light is crucial for human vision and photography. When we see our surroundings, we see only a visible range of electromagnetic waves. So, the only familiar electromagnetic waves were the visible light waves. But, we now know that electromagnetic waves include visible light waves, X-rays, gamma rays, radio waves, microwaves, ultraviolet and infrared waves. The classification of EM waves according to frequency in the electromagnetic spectrum is shown in the figure given below.

Now we will discuss all these EM waves one by one with the help of the following table

TypeWavelength rangeProductionDetection
Radio>0.1 mRapid acceleration and decelerations of electrons in aerialsReceiver's aerials
Microwave1 mmKlystron valve or magnetron valvePoint contact diodes
Infra-red1 mmVibration of atoms and moleculesThermopiles Bolometer, Infrared photographic film
Lightto 400 nmElectrons in atoms emit light when they move from one energy level to a lower energy levelThe eye Photocells Photographic film
Ultraviolet400 nm to 1 nmInner shell electrons in atoms move from one energy level to a lower levelPhotocells Photographic film
X-rays1nm to 10^{-3} nmX-ray tubes or inner shell electronsPhotographic film Geiger tubes Ionisation chamber
Gamma rays<103 nm}Radioactive decay of the nucleus-do-

Earth's Atmosphere

The Earth's atmosphere is a complex layer of gases that envelop our planet, playing a crucial role in sustaining life. Composed primarily of nitrogen (78%) and oxygen (21%), along with trace amounts of other gases like carbon dioxide and argon, the atmosphere is divided into several layers: the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. These layers regulate temperature, and weather patterns, and protect us from harmful solar radiation. In everyday life, the atmosphere influences everything from the air we breathe and the weather we experience to long-term climate patterns.

Earth’s atmosphere has the following six layers.

(i) Troposphere

The troposphere is the innermost layer of Earth’s atmosphere. i.e. it is Closest to the surface of the Earth. It is the thermal classification of the atmosphere.“Tropos” means change. This layer gets its name from the weather that is constantly changing. The troposphere is between 8 and 14 kilometers. This layer has the air we breathe and the clouds in the sky.

(ii) Stratosphere

The stratosphere is located above the troposphere and below the mesosphere. It extends between 17-50 Km above the earth's surface. The ozone layer is located in the stratosphere. Ozone layer - It absorbs most of the ultraviolet rays emitted by the sun.

(iii) Mesosphere

The mesosphere is located above the stratosphere and below the thermosphere. It is characterized by temperatures that quickly decrease with increasing height. It extends between 50-80 Km.

(iv) Thermosphere

The thermosphere is located above the mesosphere and below the exosphere. Based on the vertical temperature profile in the atmosphere, the thermosphere is the highest layer, located above the mesosphere.

In the thermosphere, temperature increases with altitude. It extends from about 90 km to between 500 and 1,000 km above our planet.

(v) Ionosphere

It starts at about 75 Km and goes up to 650 Km. It contains ions and free electrons. Aurora occurs in the Ionosphere.

(vi) Exosphere

The outermost layer of the earth's atmosphere. (640 Km - 1280 Km)

Point to remember

1. Polarisation in EM wave - For an EM wave, the direction of polarisation is taken to be the direction of the electric field.

2. Wavelength of EM Wave

$
\lambda=\frac{\lambda_o}{\mu}
$
$\lambda_o=$ Wavelength in vacuum
$\mu=$ Refractive index of the medium (Detail analysis will be studied in Optics)

Recommended Topic Video

Solved Examples Based on Electromagnetic Spectrum

Example 1: An electromagnetic wave of frequency $f=3.0 \mathrm{MHz}$ passes from a vacuum into a dielectric medium with permittivity $\epsilon_r=4.0$. Then

1) wavelength is doubled and the frequency remains unchanged

2) wavelength is doubled and frequency becomes half

3) wavelength is halved and frequency remains unchanged

4) wavelength and frequency both remain unchanged.

Solution:

Wavelength of EM Wave

$\lambda=\frac{\lambda_o}{\mu}$

wherein
$\lambda_o=$ Wavelength in vacuum
$\mu=$ Refractive index of the medium
$
\mu=\sqrt{\frac{\epsilon}{\epsilon_0}}=\sqrt{\epsilon_r}=\sqrt{4}=2
$

Since $\mu \alpha \frac{1}{\lambda}$
$\therefore \quad$ Wavelength is halved

The frequency of electromagnetic waves won't change with the change in a medium,

Hence, the answer is the option (3).

Example 2: A radar sends the waves towards a distant object and receives the signal reflected by an object. These waves are

1) Sound waves

2) Light waves

3) Radio waves

4) Microwaves

Solution:

Application of Radio and Microwaves:

These are used in radio and TV communication.

Nowadays, microwaves are used to locate flying objects by radar.

Hence, the answer is the option (4).

Example 3: Given below in the left column are different modes of communication using the kinds of waves given in the right column.

A. Optical Fibre Communication P. Ultrasound

B. Radar Q. Infrared Light

C. Sonar R. Microwaves

D. Mobile Phones S. Radio Waves

From the options given below, find the most appropriate match between entries in the left and the right column.

1) A-Q, B-S, C-R, D-P

2) A-S, B-Q, C-R, D-P

3) A-Q, B-S, C-P, D-R

4) A-R, B-P, C-S, D-Q

Solution:

Optical fiber communication $\rightarrow$ Infrared light

Radar $\rightarrow$ Radio waves

Sonar $\rightarrow$Ultrasound

Mobile phones $\rightarrow$ Microwaves

Hence, the answer is the option is (3)

Example 4: What is the name given to that part of the electromagnetic spectrum that is used for taking photographs of Earth under foggy conditions from great heights?

1) U.V. rays

2) Visible rays

3) Infrared rays

4) Microwaves

Solution:

Application of Infrared rays

1. Treat muscular pain.

2. For taking photographs in fog or smoke

3. In weather forecasting

Therefore, Infrared rays are used to take photos of Earth.

Hence, the answer is the option (3).

Example 5: Which of the following rays are used to sterilise the surgical instruments?

1) Infrared rays

2) X - rays

3) U.V. rays

4) None of these

Solution:

Application of UV rays

1. In the study of molecular structure.

2. In sterilizing the surgical instruments

3. In the detection of forged documents, fingerprints

Hence, UV rays are used for sterilizing surgical instruments.

Hence, the answer is the option (3).

Summary

The electromagnetic spectrum spans a range of electromagnetic radiation types, from radio waves to gamma rays, each with unique wavelengths and frequencies. This spectrum is vital to various technologies and scientific fields, enabling communication systems, medical imaging, and environmental monitoring. Understanding the electromagnetic spectrum helps us harness different types of radiation for practical applications, such as using infrared for thermal imaging, microwaves in radar, and ultraviolet rays for sterilizing medical instruments.

Frequently Asked Questions (FAQs)

1. What is the electromagnetic spectrum?
The electromagnetic spectrum is the complete range of all types of electromagnetic radiation. It includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. These different types of radiation are all forms of energy that travel as waves and can be characterized by their wavelength, frequency, and energy.
2. How are different types of electromagnetic waves related to each other?
All electromagnetic waves are related as they are forms of energy that travel at the speed of light in a vacuum. They differ in their wavelengths and frequencies, which are inversely related. As wavelength increases, frequency decreases, and vice versa. This relationship allows us to arrange them in order from longest wavelength (radio waves) to shortest wavelength (gamma rays) in the electromagnetic spectrum.
3. Why can we see visible light but not other parts of the electromagnetic spectrum?
Our eyes have evolved to detect only a small portion of the electromagnetic spectrum, which we call visible light. This range corresponds to wavelengths between about 380-700 nanometers. Other parts of the spectrum, such as radio waves or X-rays, have wavelengths that our eyes cannot detect. However, we have developed technologies to detect and use these other forms of electromagnetic radiation.
4. How does the energy of electromagnetic waves change across the spectrum?
The energy of electromagnetic waves increases as their wavelength decreases (and frequency increases). This means that radio waves, with the longest wavelengths, have the least energy, while gamma rays, with the shortest wavelengths, have the most energy. This relationship is described by the equation E = hf, where E is energy, h is Planck's constant, and f is frequency.
5. Can electromagnetic waves travel through a vacuum?
Yes, electromagnetic waves can travel through a vacuum. Unlike mechanical waves (such as sound waves) that require a medium to propagate, electromagnetic waves can travel through empty space. This is why we can receive light from distant stars and radio signals from space probes.
6. How do electromagnetic waves interact with matter?
Electromagnetic waves can interact with matter in several ways:
7. Why does the sky appear blue?
The sky appears blue due to a phenomenon called Rayleigh scattering. Sunlight, which contains all colors of visible light, enters Earth's atmosphere and interacts with gas molecules. These molecules scatter shorter wavelengths (blue light) more effectively than longer wavelengths (red light). The scattered blue light reaches our eyes from all directions, making the sky appear blue. At sunset, when sunlight travels through more atmosphere, longer wavelengths become more prominent, creating red and orange hues.
8. What is the relationship between temperature and electromagnetic radiation?
All objects with a temperature above absolute zero emit electromagnetic radiation. The relationship between temperature and radiation is described by black body radiation laws. As an object's temperature increases:
9. What is the significance of the cosmic microwave background radiation?
The cosmic microwave background (CMB) radiation is electromagnetic radiation left over from the early stages of the universe, about 380,000 years after the Big Bang. It's a form of microwave radiation that fills all of space. The discovery and study of the CMB provide strong evidence for the Big Bang theory and offer insights into the early universe. Its near-uniform temperature (with tiny fluctuations) across the sky helps cosmologists understand the structure and evolution of the universe.
10. How do electromagnetic waves behave differently in different media?
Electromagnetic waves behave differently in various media due to the interaction between the wave and the medium's atoms or molecules. Key differences include:
11. How do electromagnetic waves interact with the Earth's atmosphere?
Electromagnetic waves interact with the Earth's atmosphere in several ways:
12. How do metamaterials interact with electromagnetic waves?
Metamaterials are artificially engineered materials designed to have properties not found in nature. They can interact with electromagnetic waves in unique ways:
13. How do antennas work with electromagnetic waves?
Antennas are devices that convert electromagnetic waves into electrical currents (receiving) or electrical currents into electromagnetic waves (transmitting). They work based on the principle that accelerating electric charges produce electromagnetic waves, and oscillating electromagnetic fields induce currents in conductors. Key points about antennas:
14. How do we use spectroscopy to analyze the electromagnetic spectrum?
Spectroscopy is the study of the interaction between matter and electromagnetic radiation. It's used to analyze the spectrum in several ways:
15. How does the atmosphere's interaction with electromagnetic waves affect climate?
The atmosphere's interaction with electromagnetic waves significantly impacts climate:
16. What is the speed of electromagnetic waves?
All electromagnetic waves travel at the same speed in a vacuum, which is approximately 3 x 10^8 meters per second (m/s). This is commonly known as the speed of light, often denoted by the symbol 'c'. In other media, such as air or water, electromagnetic waves travel slightly slower, but their speed is still very close to c.
17. How are electromagnetic waves produced?
Electromagnetic waves are produced by accelerating electric charges. This can occur in various ways, such as electrons moving back and forth in an antenna (for radio waves), electrons transitioning between energy levels in atoms (for visible light), or charged particles being accelerated in high-energy collisions (for X-rays and gamma rays).
18. What is the relationship between wavelength and frequency in electromagnetic waves?
Wavelength and frequency in electromagnetic waves are inversely related. This means that as wavelength increases, frequency decreases, and vice versa. This relationship is described by the equation c = λf, where c is the speed of light, λ (lambda) is wavelength, and f is frequency. This equation shows that for a constant speed of light, wavelength and frequency must vary inversely to maintain their product equal to c.
19. How do we use different parts of the electromagnetic spectrum in everyday life?
We use different parts of the electromagnetic spectrum in many ways:
20. Why do some electromagnetic waves pose health risks while others don't?
The potential health risk of electromagnetic waves is related to their energy, which increases with frequency. Low-energy waves like radio waves and visible light are generally harmless in moderate amounts. However, high-energy waves like X-rays and gamma rays can ionize atoms, potentially damaging DNA and cells, which can lead to health issues. The ability of a wave to penetrate human tissue also plays a role in its potential health impact.
21. How do astronomers use the electromagnetic spectrum to study the universe?
Astronomers use the entire electromagnetic spectrum to study the universe. Different celestial objects emit radiation across various parts of the spectrum:
22. What is the difference between ionizing and non-ionizing radiation?
Ionizing radiation has enough energy to remove electrons from atoms, creating ions. This includes high-energy ultraviolet, X-rays, and gamma rays. Non-ionizing radiation doesn't have enough energy to ionize atoms and includes radio waves, microwaves, infrared, and visible light. The boundary between ionizing and non-ionizing radiation is in the ultraviolet part of the spectrum. Ionizing radiation can be harmful to living organisms as it can damage DNA and cells.
23. How do we measure the wavelength of different electromagnetic waves?
The method for measuring wavelength depends on the type of electromagnetic wave:
24. What is the photoelectric effect and how does it relate to the electromagnetic spectrum?
The photoelectric effect is the emission of electrons from a material when it's exposed to light. It demonstrates the particle nature of light, as explained by Einstein. The effect depends on the frequency (and thus energy) of the incoming light, not its intensity. Only light above a certain frequency (typically in the ultraviolet or higher energy part of the spectrum) can cause electron emission. This effect is crucial in understanding the dual nature of light as both a wave and a particle, and it's used in technologies like solar cells and light sensors.
25. How do electromagnetic waves propagate energy?
Electromagnetic waves propagate energy through oscillating electric and magnetic fields. These fields are perpendicular to each other and to the direction of wave propagation. As the wave travels, energy is transferred through space by these oscillating fields. The amount of energy carried depends on the wave's amplitude and frequency. This mechanism allows electromagnetic waves to transfer energy across vast distances, even through a vacuum, which is why we can receive energy from the Sun and distant stars.
26. How do polarized electromagnetic waves differ from unpolarized waves?
Polarized electromagnetic waves have their electric field oscillations confined to a single plane, while unpolarized waves have electric field oscillations in all directions perpendicular to the direction of propagation. Polarization can occur naturally (like in light reflected off water) or be induced artificially (using polarizing filters). Polarized waves have special properties and applications, such as in LCD screens, polarized sunglasses, and certain types of 3D movie technology.
27. What is the Doppler effect for electromagnetic waves and how is it used in astronomy?
The Doppler effect for electromagnetic waves is the change in observed frequency due to relative motion between the source and observer. When a source moves away, the waves are stretched (redshifted), and when it moves closer, they are compressed (blueshifted). In astronomy, this effect is used to:
28. What is electromagnetic interference and how can it be mitigated?
Electromagnetic interference (EMI) is the disruption of electronic device operation due to electromagnetic radiation from another source. It can cause noise in audio systems, distort video signals, or interfere with wireless communications. EMI can be mitigated through:
29. What is the relationship between Maxwell's equations and electromagnetic waves?
Maxwell's equations are a set of four fundamental equations that describe how electric and magnetic fields behave and interact. They are crucial to understanding electromagnetic waves because:
30. What is the significance of the electromagnetic spectrum in quantum mechanics?
The electromagnetic spectrum plays a crucial role in quantum mechanics:
31. What is the role of the electromagnetic spectrum in modern communication technologies?
The electromagnetic spectrum is fundamental to modern communication technologies:
32. What is the difference between coherent and incoherent electromagnetic radiation?
Coherent and incoherent radiation differ in their phase relationships:

Articles

Back to top