Electromagnetic Waves

Prerequisites are recollections of what you have learned before. It is expected to help to get ready for the new concepts presented here.

1.      Wave - A wave is a disturbance that travels through a medium from one point to another. 

If a medium is a water in the bucket filled to its rim and if we drop a small pebble right in the middle, we will see rings of disturbances (water waves) traveling outwards from the centre as shown in the figure below. These disturbances are an example wave.

The other example would be, if you tie one end of a rope to a tree and jerk the other end up and down, you will end up getting a wave as shown in the figure below.

These kinds of waves are called a transverse wave. In a transverse wave, the moment of the medium is perpendicular to the direction of motion/propagation of the wave (or direction of movement of energy).

It is important to note that the wave only transmutes energy.

Note that the dotted lines in the above figure represent a rope when it is just stretched and not disturbed. In such a state, we can say that the rope is in an equilibrium position.

There are two types of waves.

1. Mechanical Waves 

These waves require a material medium for propagation. 

Example: Water waves, sound waves, seismic waves, etc.

2. Electromagnetic waves

These waves do not require a material medium for propagation.

Sun is the main source of electromagnetic waves.

2. Wavelength - It is the distance between equivalent positions on succeeding waves. In other words, it is the distance between two consecutive crests or troughs.

It is represented by a Greek letter Lamda (λ) and is expressed in meters (m).

3.      Frequency - It is the maximum number of waves passing through a point in one second.

It is represented by small letter ‘f’ and is measured in Hertz (Hz).

It is important to note that the energy of a wave increases with an increase in frequency.

4.      Amplitude - It is the maximum height of the crest/peaks and trough are equal and are all amplitude.

It is represented by the letter ‘a’ and is measured in metres (m).

In summary, we have; 

5. The relation between frequency and wave - The frequency and wavelength of a wave depend inversely with each other. That is, if the frequency of a wave is high then its wavelength will be small and vice-versa. The opposite is also true, that is, if the wavelength of a wave is large then its frequency will be low and vice-versa.

The electromagnetic wave’s frequency multiplied by its wavelength equals the speed of light in vacuum ((299,792 m)⁄(s ≈) 3〖×10〗^8 m/s). 

These relationships are true for all electromagnetic waves. 

1.      Some common properties of electromagnetic waves are:

                                      i.      They are transverse in nature.

                                    ii.      They do not necessarily require any material medium for their transmission. They can travel through a vacuum.

                                  iii.      They travel at the speed of light in a vacuum.

                                  iv.      They undergo the phenomenon of reflection, refraction, interference, and polarization.

Electromagnetic Spectrum

The energy from the sun reaches Earth in the form of the electromagnetic spectrum. The electromagnetic spectrum is the collection of electromagnetic waves of the sun arranged in the order of their wavelength or frequency. These waves are largely categorized into seven different types and they are:

1.  Radio waves

2.  Microwaves

3.  Infrared waves (or often referred to as Infrared Radiation or IR waves)

4.  Visible light

5.  Ultraviolet waves (Or often referred to as Ultraviolet Radiation or Ultraviolet Rays)

6.  X-rays

7.  Gamma Rays

The following figure shows the arrangement of the electromagnetic waves.

Let us now explore all the electromagnetic waves, discuss what they are used for, and their effects.

1.      Radio Waves

Radio waves have the longest wavelength than any other waves in the electromagnetic spectrum.

1. Frequency: Up to 3×〖10〗^10  Hz

2. Wavelength: 10 mm or 1 cm.

Uses:

1.      It is used in broadcasting television and radio programs.

2.      In hospitals, they are used in the form of MRI (Magnetic Resonance Imaging) to detect tumors, to see inside joints, cartilage, ligaments, and tendons.

Effects:

1.      There is no definitive proof that radio waves are harmful though some suggest that overexposures to radio waves may lead to sleep disorders, headaches, and other neurological problems.

2.      Microwaves

Microwaves have lots of uses in our day-to-day life. There are two types of microwaves - long and short microwaves.

1. Frequency: Up to 3×〖10〗^9  Hz to 3×〖10〗^13  Hz.

2. Wavelength: 〖10〗^(-2)  m to 〖10〗^(-1)  m.

Uses:

1.      Microwaves are used in making point-to-point communication over varying distances because they can travel through the fog, clouds, mist, snow, etc.

2.      Longer microwaves are used in microwave ovens for cooking.

3.      Bluetooth and Wi-Fi use the microwave.

Effects:

1.      There is no definitive proof that radio waves are harmful though some studies suggest that over exposures may lead to internal bleeding of cells and lead to tumors.

3.      Infrared Radiation

If you look at the electromagnetic spectrum, infrared radiation lies just above the red light of the visible spectrum. This wave produces a heating effect and that why they are also referred to as heatwaves. There are two types of infrared radiation, namely; longer and shorter infrared radiation.

1. Frequency: Up to 3×〖10〗^13  Hz to 4×〖10〗^14  Hz.

2. Wavelength: 〖10〗^(-4)  m to 〖7.8×10〗^(-7)  m.

Uses:

1.      They are used in short-range communication.

2.      They are used in cooking as they produce a heating effect.

3.      Shorter infrared radiations do not produce heat and are used in remote controls.

Effects:

1.      The cause cataracts, corneal ulcers, and retinal burns.

2.      The overexposure to the radiation may cause skin burns.

4. Visible Light

Visible light lies in the middle of the electromagnetic spectrum. It is what helps us to see hence the name visible light.

1. Frequency: Up to 4×〖10〗^14  Hz to 8×〖10〗^14  Hz.

2. Wavelength: 〖7.8×10〗^(-7)  m to 〖3.8×10〗^(-7)  m.

Uses:

1. Visible light is used in electric bulbs and the likes to help us see.

2. It is used in photography.

Effects:

A very bright light (light of high intensity) has the potential to damage our eyes if we look at it directly. 

5.      Ultraviolet radiations/UV Rays

These radiations lie beyond the violet light of the visible spectrum. There are two types of ultraviolet radiations namely; shorter wavelength ultraviolet radiation and longer wavelength ultraviolet radiation.

1.      Frequency: Up to . 8×〖10〗^14  Hz to 3×〖10〗^16  Hz.

2.      Wavelength: 〖3.8×10〗^(-7)  m to 〖1.0×10〗^(-8)  m.

Uses:

1.      The produces vitamin D in our body.

2.      They are used for sterilizing equipment in hospitals and laboratories.

3.      They are used to detect defects in construction and production in factories.

Effects:

1.      Shorter UV rays are harmful to us because it has an ionizing effect. However, most of it is absorbed by Earth’s atmosphere.

2.      Overexposure to UV rays includes premature aging of the skin, suppression of the immune system, damage to the eyes, and skin cancer.

6.      X-rays

X-rays are also of two types; soft x-rays and hard x-rays. The following are frequency and wavelength range of soft x-rays. Hard x-rays have the same that frequency and wavelength range of gamma rays. The difference between these two is the source.

1.      Frequency: Up to . 3×〖10〗^16  Hz to 3×〖10〗^18  Hz.

2.      Wavelength: 〖10〗^(-8)  m to 〖10〗^(-10)  m.

Uses:

1.      It is used in medical diagnosis in the form of CT scans in hospitals.

2.      It is also used in airport security scanners.

Effects:

1.      They have ionizing effects therefore, overexposure to it would lead to cell mutations which may lead to cancer.

1.      Gamma Rays

Gamma rays have the highest frequencies of all the electromagnetic waves and therefore it has the highest energy. It has high penetrating power.

1.      Frequency: Up greater than 〖10〗^18  Hz.

2. Wavelength: 〖10〗^(-10)  m.

Uses:

1.      It is used in sterilizing medical equipment.

2.      It is also used in the treatment of cancer.

Effects:

1.      It also has ionizing effects. Overexposure to it can lead to cancer.

Communication through Waves

 These days the messages are sent in the form of electrical signals through high-frequency carrier waves like radio waves and microwaves because they are easily reflected, refracted, and diffracted. These interactions cause them to change their direction and reach areas otherwise inaccessible to them.

Communication over short distances

The communication between electronic devices has changed over the years. Nowadays, most of the communication is done without using wires or cables. Electromagnetic waves like radio waves, microwaves, and infrared radiation are used in wireless communication systems. This type of communication where we do not use wire or cables is called wireless communication.

Bluetooth is one example of wireless communication over a short distance. It uses the microwave. The effective range of Bluetooth is 10 m. In other words, the distance between the two devices should be less than or equal to 10 m. It is used for making point-to-point communication.

The other example of wireless communication over a short distance is the Wi-Fi (Wireless Fidelity). It also uses microwaves and its effective range is 100 m. Unlike Bluetooth, Wi-Fi multiple devices can be connected at once.

Communication over a long distance

The long-distance communication is achieved by using radio waves because it easily undergoes diffraction.

Diffraction is a phenomenon of bending and spreading of waves passing through gaps, corners, or edges of obstacles as shown in the figure below. The diffraction will be more if the gap is equal to the wavelength of the wave.

The other reason for using radio waves to communicate over a long distance is that it is reflected from the charged layer of the atmosphere called ionosphere and therefore, covers a larger area. This makes it suitable for broadcasting radio and television programs.

Microwaves are also used for communication over a long distance. As it has shorter wavelengths compared to radio waves they do not undergo diffraction hence they are not used for broadcasting radio or television programs. It can pass through the earth’s atmosphere and therefore it is used for sending and receiving signals from the satellite.