Electromagnetic spectrum is the arrangement of all the electromagnetic radiations or waves in the increasing order of their wavelengths or decreasing order of their frequencies. In simple words, the electromagnetic spectrum describes the range of many electromagnetic radiations, which differ from one another in wavelength (or frequency).
A visible light that our eyes can detect contains radiation with wavelengths between approximately 3800 Å (angstroms) and 7600 Å. Different colors in visible light correspond to radiation of different wavelengths within this range. For example, violet light has the shortest wavelength, near 3800 Å, while red light has the longest wavelength, near 7600 Å.
In addition to visible light, there are many other types of electromagnetic radiation, such as:
- X-rays
- Ultraviolet (UV) rays
- Infrared (IR) rays
- Microwaves
- Radio waves
Each type of electromagnetic radiation has its own specific range of wavelengths and frequencies, and these ranges together constitute what is called the electromagnetic radiation spectrum or simply electromagnetic spectrum.
Understanding Regions of Electromagnetic Spectrum
Electromagnetic spectrum consists of various types of electromagnetic radiations having different wavelengths (or different frequencies). The electromagnetic spectrum is divided into several regions, ordered by either increasing wavelength or decreasing frequency. Each region of the spectrum is identified by a specific name based on its unique range of wavelengths or frequencies. The below figure shows a complete electromagnetic spectrum.
As you can see in the above figure, all types of electromagnetic radiation have different frequencies, wavelengths, and applications. For example, radio waves have the longest wavelengths and lowest frequencies, while gamma rays have the highest frequencies and shortest wavelengths. The increasing order of wavelength (or decreasing order of frequency) is as follows:
Gamma rays < X-rays < Ultraviolet (UV) rays < Visible light < Infrared (IR) rays < Microwaves < Radio waves
Table: Electromagnetic Spectrum
| Name | Frequency (Hz) | Wavelength (m) | Uses |
|---|---|---|---|
| Gamma rays | 1020 to 1024 | 10-12 | Cancer treatment |
| X-rays | 1017 to 1020 | 10-10 | Medical “pictures” |
| Ultraviolet | 1016 to 1017 | 10-7 | Material testing |
| Visible | 1014 to 1016 | 10-6 | Electric bulb, Sun rays |
| Infrared | 1011 to 1013 | 10-4 | Illumination |
| Microwave | 109 to 1011 | 10-2 | Heating, cooking |
| Radio waves | 105 to 109 | 102 | Signal transmission |
Solved Examples on Electromagnetic Spectrum
Example 1: Calculate its frequency and wave number if the wavelength of certain light radiation is 500 nanometer.
Solution :
Wavelength of light (λ) = 500 nm = 5 * 10-9 m
Velocity of light (c) = 3 * 108 ms-1
Since Frequency (ν) = c / λ = 3 * 108 ms-1 / 5 * 10-9 m = 6 * 1014 s-1 or Hz (Ans)
Wave number (k) = 1 / λ = 1 / 5 * 10-9 m = 2 * 106 m-1 (Ans.)
Example 2: Calculate the wavelength of electromagnetic radiation transmitted by transmitter if the radio is transmission is done at 980 kHz frequency by Dhanbad transmission center.
Solution :
Frequency of the radiation ν = 980 kHz
Wavelength = Velocity / Frequency = 3 * 108 ms-1 / 980 * 10-3 s-1 = 306 m (Ans.)
Example 2: Calculate wave number and frequency of yellow radiation having wavelength 5800 Å.
Solution :
Wavelength = 5800 Å = 5800 × 10–8 cm = 5800 × 10–10 m
(A) Calculation of wave number:
Wave number = 1 / wavelength = 1 / 5800 × 10–10 m = 1.724 × 10–6 m (Ans.)
(B) Calculation of frequency:
Frequency ν = Velocity / Wavelength = 3 * 108 ms-1 / 5800 × 10–10 m = 5.172 × 1014 Hz (Ans.)
Example 3: The wavelength range of the visible spectrum extends from violet (400 nanometer) to red (750 nanometer). Convert these wavelengths into frequencies (Hz).
Solution :
Frequency of violet light = Velocity of light / Wavelength = 3 * 108 ms-1 / 400 × 10–9 m = 7.50 × 1014 Hz.
Frequency of red light = 3 * 108 ms-1 / 750 × 10–9 m = 4.00 × 1014 Hz.
Thus, the frequency range of the visible spectrum is from 4.0 × 1014 to 7.5 × 1014 Hz (Ans.)
Example 4: Compute the wavelength of the electromagnetic radiation emitted by the transmitter if the Vividh Bharati station of All India Radio, Delhi, broadcasts on a frequency of 1,368 kilo hertz. Which part of the electromagnetic spectrum does it belong to?
Solution :
We know that the wavelength (λ) is equal to c/ν, where c is the speed of electromagnetic radiation in a vacuum and ν is the frequency.
Wavelength = Velocity / Frequency = 3 * 108 ms-1 / 1368 * 103 s-1 = 219.3 m. This is the characteristics of radio wave wavelength.
