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Electromagnetic radiation can be understood as a flow of energy wherein the magnetic and electrical fields change simultaneously. Some of the examples of electromagnetic radiation include X-rays, radio waves, microwaves, UV light, etc. The electromagnetic waves have a dual nature, that means it can act both as a particle and as a wave.
What is Electromagnetic Radiation (EMR)?
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Electromagnetic radiation is an energy flow in which both electrical and magnetic fields change at the same time. Sir James Clerk Maxwell, a Scottish scientist, proposed the theory of electromagnetic radiation in the early 1870s. Heinrich Hertz, a German physicist, confirmed it experimentally.
When an electrically charged particle accelerates, time alternating electrical and magnetic fields are formed, according to Maxwell, which aids the particle's propagation. Radio waves, infrared light, microwaves, X-rays, visible light, ultraviolet light, and gamma rays are examples of electromagnetic radiation. Electromagnetic radiations travel through oscillating electrical and magnetic fields formed by their particles in space and vacuum.
The electromagnetic waves are dual in nature. It has the ability to behave like both a wave and a particle. The velocity, frequency, and wavelength of a wave describe its nature as a wave.
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Wave Nature of Electromagnetic Radiation
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On a macroscopic level, James Maxwell (1870) was the first to provide a full explanation of the interaction between charged objects and the behavior of electrical and magnetic fields. He proposed that alternating electrical and magnetic fields are formed and transmitted as electrically charged particles and moves under acceleration. Electromagnetic waves, also known as electromagnetic radiation, are used to transmit these fields.
Light is a type of radiation that has been recognized since the dawn of humanity. The light was once thought to be made up of particles (corpuscles). The wave nature of light was only discovered in the 19th century.
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Electromagnetic Radiation Properties
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- When charged particles oscillate, they produce oscillating electric and magnetic fields that are both perpendicular to each other and to the wave's propagation direction.
- Electromagnetic waves can even travel in a vacuum too, i.e. they don't need a medium to move.
- There are numerous different types of electromagnetic radiation, each with its own wavelength or frequency.
- The electromagnetic spectrum is made up of all of this electromagnetic energy. Radiofrequency, microwave, infrared, ultraviolet, visible, and other wavelengths are examples of electromagnetic radiation.
- Various aspects of electromagnetic radiation, such as frequency, wavelength, and time period, are used to classify these radiations.
- Electromagnetic waves travel at a speed of 3 x 108 m/s in the vacuum. This is the speed of light.
The three factors that define the wave nature of electromagnetic radiation are as follows:
- Frequency: Frequency, symbolized by the letter v, is the number of waves that travel through a certain point in one second. Its SI unit is Hertz (Hz).
- Wavelength: The wavelength, symbolized by the symbol λ, is the distance between two adjacent crests or troughs of a wave or the distance between one full cycle of the oscillation.
- Velocity: In a vacuum, the speed of an electromagnetic wave is 3 x 108 m/s. The velocity of a wave, which is calculated by multiplying the wavelength and frequency can be expressed as:
Velocity = λv
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Relation Between Frequency and Energy
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As the frequency rises, so does the energy. As a result, frequency and energy are proportionate. It can be expressed in the following way:
Formulae for Electromagnetic Radiation
The number of waves passing through a specific point in a second is referred to as frequency. It is equal to the reciprocal of the time period of electromagnetic radiation in mathematics. The following is a general equation that relates the speed of light, frequency, and wavelength of electromagnetic radiation:
One of the other factors used to characterize electromagnetic radiation in addition to frequency and wavelength is Wavenumber. It is the number of wavelengths per unit length. It is mathematically equal to the reciprocal of the wavelength. It is defined by the expression m-1 in the SI unit.
Read More: Energy Consideration: A Quantitative Study with Lenz Law
Sample Questions
Ques. What are some examples of electromagnetic waves? (1 Mark)
Ans. Radio and television waves, microwaves, infrared rays, visible light, ultraviolet light, X-rays, and gamma rays are all examples of electromagnetic waves that propagate across space.
Ques. All India Radio's Vividh Bharati station in Delhi broadcasts on a frequency of 1,368 kHz (kilohertz). Calculate the wavelength of the transmitter's radiated electromagnetic radiation. Which part of the electromagnetic spectrum does it belong to? (1 Mark)
Ans. The wavelength (λ) is equal to c/ν. Here c is the speed of electromagnetic radiation in a vacuum and ν is the frequency.
So, we have
λ = c/ν
= 3.00 x 108 m/s/1368 kHz
= 3.00 x 108 m/s /1368 x 103/s
= 219.3m
This is the characteristic radio wave wavelength.
Ques. The range of the wavelength of the visible spectrum extends from violet(400 nm) to red(750 nm). Express these wavelengths in frequencies (Hz). (1nm = 10–9 m) (2 Marks)
Ans. The frequency of violet light:
v= c/λ
= 3.00 x 108 m/s / 400 x 10-9 m
= 7.50 x 1014 Hz
The frequency of red light
v=c/λ
= 3.00 x 108 m/s / 750 x 10-9 m
= 4.00 x 1014 Hz
Hence, the range of the visible spectrum is from 4.0 × 1014 to 7.5 × 1014 Hz in terms of frequency units.
Ques. Is it safe for people to be exposed to electromagnetic radiation? (1 Mark)
Ans. Short-term exposure to extremely high levels of electromagnetic fields can certainly be damaging to one's health. However, despite extensive studies, there’s no reason to believe that low-level exposure to electromagnetic radiation is harmful to our health.
Ques. Is electromagnetic energy considered a form of light? (1 Mark)
Ans. Radio waves, gamma rays, visible light, and the rest of the electromagnetic spectrum are all examples of electromagnetic radiation. These radiations can be depicted as a stream of mass-less particles, known as photons, that travel at the speed of light in a wave-like pattern.
Ques. How do electromagnetic wave’s magnetic and electrical components travel? (1 Mark)
Ans. The oscillating electric and magnetic fields travel in a bundle of light energy called a photon at right angles to each other. An electromagnetic wave's magnetic and electric fields are perpendicular to each other and to the wave's direction.
Ques. What is the nature of waves? (1 Mark)
Ans. A longitudinal wave is a disturbance that flows through a medium like air or water. These fluids are thought to be made up of a large number of particles, each made up of a large number of molecules.
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