Electromagnetic waves are all around you— the radio you listen to, the TV you watch, the microwave oven you use for cooking, and the X-rays your doctor uses. All employ electromagnetic waves. But what are electromagnetic waves? Learn in detail about electromagnetic waves, their types and examples.
What is an Electromagnetic Wave?
Electromagnetic waves definition: The waves produced when an electric field comes in contact with the magnetic field are called electromagnetic or EM waves. They are a composition of oscillating magnetic and electric fields that can be studied using Maxwell’s equations.
The electromagnetic waves can be radio waves, microwaves, television waves, and more. The differing types arise from the difference in wavelength and frequency.
How are Electromagnetic Waves Formed?
- A charged particle gives rise to an electric field.
- This electric field applies a force on other charged particles.
- Positive charges get accelerated towards the direction of the electric field. Contrastingly, negative charges get accelerated in the opposite direction.
- The moving charged particle gives rise to a magnetic field.
- This magnetic field exerts a force on other charged moving particles.
- This force is perpendicular to the velocity direction; thus, it changes their velocity, not the speed.
- As a result, an accelerating charged particle gives rise to an electromagnetic field.
- Therefore, you can say that electromagnetic waves are magnetic and electric fields travelling via free space with the speed of light c.
- When the charged particle oscillates around an equilibrium position, it is termed an accelerating charged particle.
- So, if its frequency of oscillation is f, the electromagnetic wave it produces will also have a frequency (f).
- The following equation can give the wavelength λ of the electromagnetic wave:
λ = c/f
Properties of Electromagnetic Waves
Following are some key postulates regarding electromagnetic waves:
- Electromagnetic waves are transverse in nature.
- An accelerating charge can produce them.
- They require no medium for propagation.
- The direction of variation of electric (E) and magnetic (B) fields are perpendicular to each other and also perpendicular to the direction of propagation (c).
- The following formula gives the frequency of an electromagnetic wave:
- The variation in electric and magnetic field components remains in the same phase. So, the phase difference is zero.
- The magnitude of E and B are related as follows:
c = EB
- The energy of an EM wave is divided on average equally between E and B.
- The following formula gives the speed of an electromagnetic wave in a vacuum:
Derivation of the Speed of EM Waves Formula
The formula for the speed of an electromagnetic wave in a vacuum can be derived as follows:
Since 1/ 4πεο = 9 x 109 and µ0 = 4π × 10-7
Writing µ0 = 4π × 10-7 as o4=10-7
On dividing the two equations: 1/4πεο= 9 x 109 by μο/4π =10-7
You get 1/μoεο = 9 × 1016
It can be written as 1oo = (3 × 108 )2
Since it is known that 3 × 108 = c
So, the equation can be written as follows:
1/μoεο = c2
|Example 1. What is the wavelength of an infrared light photon that has a frequency of 2 x 1014 Hz? |
Solution: Infrared light lies in the electromagnetic spectrum. So, its relation between the frequency, wavelength, and velocity can be studied using the following formula:
λ = c/f
Since c = 3 x 108 m/s and the given frequency is 2 x 1014 Hz, the value of the wavelength can be calculated using the wavelength formula.
λ = c/f
λ =3 x 108/2 x 1014
λ = 1.5 x 10-6m
What is an Electromagnetic Spectrum?
The range of electromagnetic waves frequencies and their respective wavelengths and photon energies is called an electromagnetic spectrum.
To understand the electromagnetic spectrum, one should know about wavelength and frequency. Wavelength is the distance between adjacent crests in the adjacent cycles of a waveform signal. While the top part is the crest, the bottom is a trough. The long waves have a low frequency and energy, while the shorter waves have a comparatively high frequency and energy.
|Points to Remember |
Gamma → X-rays → Ultraviolet → Visible → Infrared →Micro →Radio
Crest, Trough, and Wavelength
So, an electromagnetic spectrum comprises waves of different wavelengths, from very long radio waves to short gamma rays. The electromagnetic spectrum includes the following waves, as shown in the figure. In order of their increasing wavelength, the rays are as follows:
Gamma rays < X rays < UV rays < Visible Light < Infrared rays < Microwaves < Radio waves
Electromagnetic Waves Examples and Their Uses
The electromagnetic spectrum includes several electromagnetic wave types. Here is in detail about each one of them.
The waves with the longest wavelengths among all the EM waves. They can be a foot long or even up to several miles in length. These waves find application in data transmission via radio, satellites, computers, and radar.
Shorter than radio waves, these microwaves measure in centimetres. They are extensively used as they can penetrate smoke, clouds, and light rain. The universe has immense cosmic microwave background radiation that scientists connect with the Big Bang.
In between microwaves and visible light regions, infrared waves are often classified into near and far categories. Near-infrared waves lie closer to visible light, and they find applications in TV remotes to switch from one channel to another. Far infrared waves are away from visible light in wavelength and give off heat.
The light spectrum that the human eye can see is called the visible light spectrum. It covers wavelengths from 390 to 700 nm.
UV rays are the next shortest wavelength rays largely emitted from the sun. The ozone layer protects the earth from the sun’s harmful ultraviolet rays. Often some insects like bumblebees can see ultraviolet light. Powerful telescopes use UV rays to see the stars.
As discovered by Roentgen, X-rays have even shorter wavelengths than UV rays. They can penetrate soft tissue and provide a picture of bones. Multiple exposures to X-rays carry a risk of cancer, but this risk is quite small.
They are the shortest waves in the spectrum with the highest energy. Gamma rays find applications in cancer treatments and detailed imaging for diagnostic purposes.
The following table enumerates the uses of electromagnetic waves:
|Gamma rays||10-14 to 10-10m||It provides information about the structure of atomic nuclei |
It has medical applications too.
|X-rays||10-11to 3 ×10-8m||It reveals the structure of inner atomic electron shells and crystals. |
Helps in medical diagnosis.
Assists in industrial radiography
|UV rays||10-8 to 4 × 10-7m||Helps in the detection of invisible writing, forged documents and fingerprints. |
It helps detect forged currency as real banknotes do not turn fluorescent under UV light.
Helps in preserving foodstuffs and detecting adulteration
Used in water sterilisation
|Visible rays||4 ×10-7to 8 ×10-7m||Reveals structure of molecules and arrangement of electrons in external shells of atoms. |
Allows you to see objects
|Infrared rays||8×10-7 to 5 × 10-3m||In greenhouse effect, it is responsible for keeping plants warm |
It helps to look through haze, fog, and mist in wars.
Helps cure crop diseases
Treats muscular strains
|Microwaves||10-3 to 3 × 10-1m||In radar |
Long-distance wireless communication via satellites
In microwave ovens
|Radio waves||10-1 to 10-4m||In radio and television communication systems |
Marine and navigation use
Propagation of Electromagnetic Waves
The sequence of electromagnetic wave movement is as follows:
Generation → propagation → reflection → reception
The EM waves can be propagated from the transmitter to the receiver in the following ways:
- Ground waves: They can be propagated along the surface of the ground, and the process is called ground wave propagation.
- Skywaves: When the EM waves are propagated via sky, it is called sky wave propagation. In this type of propagation, the waves get reflected back to the earth from the ionosphere.
- Space waves: EM waves often propagate from the transmitter to the receiver antenna without any reflection or refraction; then, it is called space wave propagation.
Frequently Asked Questions
1. Why can photons travel at the speed of light but other particles cannot?
A. Photons can travel at light’s speed, but other particles cannot because photons do not have mass. So, all the massless particles can travel at light’s speed, including the gluon and photon.
2. Can X-rays and radio waves travel at the same speed?
A. Yes, they can. Any wave belonging to the electromagnetic spectrum travels at a constant speed: the speed of light. The other properties can differ depending on the type of wave and its sources, such as energy, frequency, and wavelength, but the speed remains constant.
3. How are gamma rays and X rays produced?
A. Gamma rays are produced in nuclear reactions, while X rays are emitted when metal is bombarded with high-speed electron/electrons.
Electromagnetic waves are an integral part of our everyday life. They have vast applications in different fields ranging from medical, army, and navigation to our household appliances. They play a vital role in communication and have contributed immensely to making our lives easier.