JEE Mains Physics · Electromagnetic Waves
Electromagnetic Spectrum: Order, Sources and Uses
Electromagnetic waves run from γ-rays to radio waves in order of increasing wavelength, and each band has its own way of being produced and its own uses.
Why this matters
Sixteen PYQs, all multiple choice, and two from 2026. Nine ask for the order of the bands or their wavelength ranges, sometimes after a short calculation that turns a frequency or a photon rate into a wavelength. Seven match a band to how it is produced or what it is used for. These are recall marks: the two tables on this page cover every one of them.
Concept 1 of 2: Order and wavelength ranges of the electromagnetic spectrum
Every band is the same kind of wave, travelling at c in vacuum; only the wavelength differs. Line them up from shortest to longest and the frequency and the photon energy fall in the same order. Learn the seven names in order and the rough edge of each band.
Definition
- Increasing wavelength: γ-rays, X-rays, ultraviolet, visible, infrared, microwaves, radio waves. Increasing frequency is the reverse order.
- Visible light runs from violet (about 400 nm) to red (about 700 nm). Colours differ in both frequency and wavelength.
- From a frequency to a band: .
- Photon energy , about eV with in nm. From a source of power P emitting N photons per second, .
- The edges are rough and neighbouring bands overlap; X-rays and γ-rays overlap most, and are told apart by their source.
| Band | Wavelength range | Frequency range | Photon energy |
|---|---|---|---|
| γ-rays | shorter than 10⁻³ nm | above 3 × 10²⁰ Hz | above 1.24 MeV |
| X-rays | 1 nm to 10⁻³ nm | 3 × 10¹⁷ to 3 × 10²⁰ Hz | 1.24 keV to 1.24 MeV Shorter than ultraviolet, longer than γ-rays. |
| Ultraviolet | 400 nm to 1 nm | 7.5 × 10¹⁴ to 3 × 10¹⁷ Hz | 3.1 eV to 1.24 keV |
| Visible | 700 nm to 400 nm | 4.3 × 10¹⁴ to 7.5 × 10¹⁴ Hz | 1.8 eV to 3.1 eV |
| Infrared | 1 mm to 700 nm | 3 × 10¹¹ to 4.3 × 10¹⁴ Hz | 1.24 meV to 1.8 eV |
| Microwaves | 0.1 m to 1 mm | 3 × 10⁹ to 3 × 10¹¹ Hz | 12.4 µeV to 1.24 meV |
| Radio waves | longer than 0.1 m | below 3 × 10⁹ Hz | below 12.4 µeV |
Wavelength rises down the table; frequency and photon energy fall.
Practice this conceptself-check · 4 quick reps
The same idea in a real exam question:
JEE Mains · 2024 · 4 April 2024 · Q95Moderate
Example 1 · Electromagnetic Waves · Electromagnetic Spectrum: Order, Sources and Uses
Arrange the following in the ascending order of wavelength: (A) Gamma rays (B) x-ray (C) Infrared waves (D) Microwaves Choose the most appropriate answer from the options given below :
γ-rays are shorter than X-rays
In an order question γ-rays come first, with the shortest wavelength. Swapping γ-rays and X-rays is the commonest wrong option.
More energetic means shorter wavelength
A higher photon energy means a higher frequency and a shorter wavelength. Infrared is more energetic than microwaves, so light used in optical fibres has a shorter wavelength than radar microwaves.
Convert each end of a band separately
Wavelength goes as 1/f, so a range of frequencies does not turn into a range of wavelengths by converting the difference. Find λ = c/f at each end, then subtract.
Concept 2 of 2: Sources, detectors and uses of each band
Each band comes from a process whose energy matches its photons. Slow, large-scale charge motion in aerials gives radio waves; vibrating molecules give infrared; electrons jumping between outer levels give light; electrons falling into deep inner shells give X-rays; and the nucleus itself gives γ-rays. Learn the source with the band, and most uses follow from the energy.
Definition
- Radio waves: rapid acceleration and deceleration of electrons in aerials.
- Microwaves: special valves, the klystron, the magnetron and the Gunn diode.
- Infrared: vibrations of atoms and molecules; every hot body.
- Visible and ultraviolet: electrons in atoms dropping from a higher energy level to a lower one; ultraviolet also from very hot bodies such as the sun.
- X-rays: inner-shell electrons moving to a lower level, as when fast electrons strike a metal target in an X-ray tube.
- γ-rays: radioactive decay of nuclei.
| Band | Produced by | Detected by | Main uses |
|---|---|---|---|
| Radio waves | Rapid acceleration and deceleration of electrons in aerials | Receiving aerials | Radio and television broadcasting, mobile communication |
| Microwaves | Klystron valve, magnetron valve, Gunn diode | Point-contact diodes | Radar, aircraft navigation, microwave ovens Klystron and magnetron both mean microwaves. |
| Infrared | Vibrations of atoms and molecules; hot bodies | Thermopiles, bolometers, infrared photographic film | Physiotherapy heat lamps, greenhouse effect, remote controls, seeing through fog |
| Visible light | Electrons in atoms dropping between outer energy levels | The eye, photocells, photographic film | Vision, photography, optical communication |
| Ultraviolet | Electron transitions in atoms; the sun and arc lamps | Photocells, photographic film | Sterilising surgical instruments, purifying water, Lasik eye surgery |
| X-rays | Inner-shell electron transitions; fast electrons striking a metal target | Photographic film, Geiger tubes, ionisation chambers | Medical diagnosis, cancer treatment, study of crystal structure A metal target hit by fast electrons gives X-rays, not γ-rays. |
| γ-rays | Radioactive decay of nuclei | Photographic film, Geiger tubes, ionisation chambers | Destroying cancer cells, sterilising medical equipment |
The source sets the band: the deeper inside the atom, the shorter the wavelength.
Practice this conceptself-check · 4 quick reps
The same idea in a real exam question:
JEE Mains · 2026 · 24 Jan 2026 Shift 1 · Q10Moderate
Example 2 · Electromagnetic Waves · Electromagnetic Spectrum: Order, Sources and Uses
Match the List-I with List-II
Choose the correct answer from the options given below:
| List-I | List-II |
|---|---|
| (A) Radio-wave | (I) is produced by Magnetron valve |
| (B) Micro-wave | (II) Due to change in the vibrational modes of atoms |
| (C) Infrared-wave | (III) Due to inner shell electrons moving from higher energy level to lower energy level |
| (D) X-ray | (IV) Due to rapid acceleration of electrons |
Inner shells give X-rays, the nucleus gives γ-rays
Both bands are very short, but X-rays come from electrons falling into inner shells of an atom, and γ-rays come from the decay of a nucleus. A match list pairs each with the other's source.
Radar uses microwaves
Radar and aircraft navigation work with microwaves, not radio waves. The short wavelength gives a sharp beam and a clear echo.
The greenhouse effect is infrared
The earth radiates infrared, and the atmosphere traps part of it. The greenhouse effect belongs with infrared, not ultraviolet.
Ultraviolet sterilises, X-rays image
Ultraviolet kills germs on instruments and in water but does not pass through the body. X-rays pass through soft tissue, so they are the band for medical images.
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (2)
Order and wavelength ranges of the electromagnetic spectrum7 rows
| Band | Wavelength range | Frequency range | Photon energy |
|---|---|---|---|
| γ-rays | shorter than 10⁻³ nm | above 3 × 10²⁰ Hz | above 1.24 MeV |
| X-rays | 1 nm to 10⁻³ nm | 3 × 10¹⁷ to 3 × 10²⁰ Hz | 1.24 keV to 1.24 MeV Shorter than ultraviolet, longer than γ-rays. |
| Ultraviolet | 400 nm to 1 nm | 7.5 × 10¹⁴ to 3 × 10¹⁷ Hz | 3.1 eV to 1.24 keV |
| Visible | 700 nm to 400 nm | 4.3 × 10¹⁴ to 7.5 × 10¹⁴ Hz | 1.8 eV to 3.1 eV |
| Infrared | 1 mm to 700 nm | 3 × 10¹¹ to 4.3 × 10¹⁴ Hz | 1.24 meV to 1.8 eV |
| Microwaves | 0.1 m to 1 mm | 3 × 10⁹ to 3 × 10¹¹ Hz | 12.4 µeV to 1.24 meV |
| Radio waves | longer than 0.1 m | below 3 × 10⁹ Hz | below 12.4 µeV |
Wavelength rises down the table; frequency and photon energy fall.
Sources, detectors and uses of each band7 rows
| Band | Produced by | Detected by | Main uses |
|---|---|---|---|
| Radio waves | Rapid acceleration and deceleration of electrons in aerials | Receiving aerials | Radio and television broadcasting, mobile communication |
| Microwaves | Klystron valve, magnetron valve, Gunn diode | Point-contact diodes | Radar, aircraft navigation, microwave ovens Klystron and magnetron both mean microwaves. |
| Infrared | Vibrations of atoms and molecules; hot bodies | Thermopiles, bolometers, infrared photographic film | Physiotherapy heat lamps, greenhouse effect, remote controls, seeing through fog |
| Visible light | Electrons in atoms dropping between outer energy levels | The eye, photocells, photographic film | Vision, photography, optical communication |
| Ultraviolet | Electron transitions in atoms; the sun and arc lamps | Photocells, photographic film | Sterilising surgical instruments, purifying water, Lasik eye surgery |
| X-rays | Inner-shell electron transitions; fast electrons striking a metal target | Photographic film, Geiger tubes, ionisation chambers | Medical diagnosis, cancer treatment, study of crystal structure A metal target hit by fast electrons gives X-rays, not γ-rays. |
| γ-rays | Radioactive decay of nuclei | Photographic film, Geiger tubes, ionisation chambers | Destroying cancer cells, sterilising medical equipment |
The source sets the band: the deeper inside the atom, the shorter the wavelength.
Watch out for (7)
- γ-rays are shorter than X-rays→ Order and wavelength ranges of the electromagnetic spectrum
- More energetic means shorter wavelength→ Order and wavelength ranges of the electromagnetic spectrum
- Convert each end of a band separately→ Order and wavelength ranges of the electromagnetic spectrum
- Inner shells give X-rays, the nucleus gives γ-rays→ Sources, detectors and uses of each band
- Radar uses microwaves→ Sources, detectors and uses of each band
- The greenhouse effect is infrared→ Sources, detectors and uses of each band
- Ultraviolet sterilises, X-rays image→ Sources, detectors and uses of each band
Test yourself on Electromagnetic Waves
20 past JEE Mains questions from this chapter, timed at 48 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.