Electromagnetic Waves

Electromagnetic waves are a key part of physics, playing an essential role in many natural events and modern technologies. These waves are made up of electric and magnetic fields that oscillate and travel through space, carrying both energy and information. The idea of electromagnetic waves was first introduced by James Clerk Maxwell in the 19th century and later confirmed by Heinrich Hertz through experiments. These waves are characterized by their wavelength, frequency, and amplitude, and they cover a broad range called the electromagnetic spectrum.

1.0Displacement Current

• When applying Ampere’s circuital law to identify the magnetic field at a point external to a capacitor connected to a time-varying current, Maxwell observed a discrepancy in the law.
• He suggested the occurrence of an additional current, termed by him, the displacement current to remove this inconsistency.
• James Clerk Maxwell  asserted that this was actually the case – not only an electric current but also a time-changing electric field creates a magnetic field.

2.0Difference Between Displacement Current and Conduction Current

3.0Maxwell’s Equations

1. Gauss’ Law in Electrostatics

$\oint \vec{E}.\overrightarrow{dA}=\frac{Q_{enc}}{{ϵ}_0}$

2. Gauss’ Law in Magnetism

$\oint \vec{B}.\overrightarrow{dA}=0$

3. Maxwell-Faraday’s Law

$\oint \vec{E}.\overrightarrow{dI}=-\frac{d{\varphi }_B}{dt}$

4.0Definition of Electromagnetic Waves

Electromagnetic waves consist of sinusoidally time varying Electric and Magnetic fields. Electric and magnetic fields oscillate sinusoidally in perpendicular planes as well as the direction the propagation of waves, so EMW are transverse in nature.

5.0Momentum of Electromagnetic Waves and Radiation Pressure

Momentum of Electromagnetic Waves

The EM wave during its propagation has linear momentum associated with it. The linear momentum carried by the portion of wave having energy U is given by

$p=\frac{U}{C}$

Radiation Pressure

The mechanical pressure applied upon any surface due to the exchange of momentum between the surface and the electromagnetic wave.

$P_R=\frac{F}{A}$

6.0Electromagnetic Spectrum

• It  is defined as the span of all types of electromagnetic radiation.
• EM Spectrum is a range of frequencies, wavelengths and photon energies covering frequencies from above 1 Hz to below $10^{25}Hz$ corresponds to wavelengths which are a few kilometres to a segment of dimension of an atomic nucleus in the spectrum of EM Waves.
• The EM spectrum encompasses all electromagnetic radiation, divided into subranges like infrared, visible light, and ultraviolet radiation.
• EM Spectrum ranges from radio waves to cosmic rays, increasing in frequency and decreasing in wavelength.