EM Waves: Key Concepts, Laws, and Properties

Radiation has to do with ... ?

Electromagnetic (EM) waves

Components of EM waves

Electric and magnetic components, which oscillate orthogonal to each other.

Coulomb's Law

The electric field at any point is determined entirely by the distribution of electric charge in the surrounding space.

Faraday's Law

Magnetic fields are determined by the distribution of electric current in a point's surroundings.

How does a changing magnetic field affect electric fields?

A changing magnetic field induces an electric field that can drive a current.

Key characteristics of EM waves

EM waves carry energy, propagate at the speed of light in a vacuum, travel perpendicular to the wave crest, and can move slower than light in natural media.

Speed of light in a vacuum

c = 3 x 10^8 m/s.

What is the relationship between wavelength (λ) and frequency (ν) of EM waves?

λ = c/ν.

What is 1 Hz equivalent to?

1 s⁻¹

Monochromatic radiation

Radiation at a single frequency.

Broadband radiation

Radiation that is a mixture of a wide range of frequencies.

Coherent radiation

Radiation that operates in unison, meaning it is in the same phase.

Incoherent radiation

Radiation that operates independently, without a consistent phase relationship.

Doppler shift

The frequency shift observed when the distance between the source and receiver changes over time.

What is the significance of Fourier decomposition in EM waves?

It allows us to analyze any arbitrary EM disturbance as a composite of different 'pure' periodic fluctuations.

How do natural sources of EM radiation vary?

They can cover broad ranges of frequency and intensity, such as the sun or lightning.

What is the typical behavior of natural radiation in the atmosphere?

Natural radiation is practically incoherent.

What is the significance of the speed of light in EM wave propagation?

It is the maximum speed at which EM waves can propagate in a vacuum.

What happens to EM waves in natural media?

They almost always move slower than the speed of light in a vacuum.

Polarization of EM waves

A fundamental property defined by the oscillation of the electric field (E field), used for observing the atmosphere.

Common types of EM wave polarizations

Linear horizontal, Linear vertical, Linear at 45º, Circular, Elliptical.

What happens to natural emissions of radiation in the atmosphere?

They are completely unpolarized but can become polarized during interactions with particles or the Earth's surface.

How does a smooth water surface affect radiation?

It preferentially reflects radiation with horizontal linear polarization, which can be filtered by polarized sunglasses.

EMR energy content [?]

Joules (J).

EMR rate of energy transfer [?]

Watts (W), where 1 W = 1 J s-1.

Flux density (in the context of EMR)

The measure of energy transfer over an area, expressed in watts per square meter (W m-2).

What geometric considerations are important in solving atmospheric radiation problems?

Spheres, such as the sun, and factors like power/intensity, wavelength, and emission properties.

What are the three possible outcomes when radiation encounters an object?

1. Scattering (or reflection)

2. Absorption (converted to thermal energy)

3. Nothing.

What happens when radiation encounters a change in media?

It can result in reflection, transmission (without refraction), or transmission (with refraction).

Maxwell's equations

Used to mathematically define electromagnetic (EM) waves.

Solutions involve a time-harmonic component and a plane wave solution, often expressed using complex numbers.

Plane wave

An EM wave that is invariant over a horizontal plane perpendicular to the direction of propagation.

Isotropic radiation

Radiation that is equal in all directions.

Solid angle

It relates to the field of view and is important for understanding radiation distribution.