Why is the orientation of the portable radio with respect to broadcasting is important?

The radio's orientation is crucial as electromagnetic waves are plane polarized, requiring the antenna to align with the wave's electric or magnetic field.

Why does a microwave oven heat food containing water molecules more efficiently?

Microwaves heat up the food items containing water molecules most efficiently because the frequency of microwaves matches the resonant frequency of water molecules.

Although an electric field E exerts a force qE on a charged particle, why does the electric field of an EM wave not contribute to radiation pressure, but only transfer energy?

Since, the electric field of an EM wave is an oscillating field and so is the electric force caused by it on a charged particle. This electric force averaged over an integral number of cycles is zero, since its direction changes every half cycle. Hence, the electric field is not responsible for radiation pressure.

It is necessary to use satellites for long distance TV transmission. Why?

Television signals are not reflected back by the layer of atmosphere called ionosphere thus TV signals from air earth station are reflected back to the earth by means of an artificial satellite.

If Earth lacked an atmosphere, would its average surface temperature be higher or lower than it is today?

The infra-red radiations get trapped inside the earth’s atmosphere due to the green greenhouse effect which makes the earth warm. Therefore the average temperature of the earth would have been low.

Photoelectric EffectJEE MathsJEE Chemistry

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

Conduction Current $I_{c}$

Displacement current $I_{d}$

Due to flow of charge in the conducting

wire.

Due to variable electric field between

plates of charging capacitors.

Denoted by $I_{c}$

$I_{c} = \frac{d q}{d t}$

Denoted by $I_{d}$

$i_{d} = ϵ_{0} \frac{d ϕ _{E}}{d t}$

3.0Maxwell’s Equations

Gauss’ Law in Electrostatics

$\oint E . d A = \frac{Q _{e n c}}{ϵ _{0}}$

Gauss’ Law in Magnetism

$\oint B . d A = 0$

Maxwell-Faraday’s Law

$\oint E . d I = - \frac{d ϕ _{B}}{d t}$

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 $1 0^{25} Hz$ 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.

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