2. Light waves, velocity of light in vacuum and transparent materials, Poynting vector (3p.)

Question 1

Light waves

Answer 1

Electromagnetic waves self-propagating transverse oscillating waves of electric and magnetic fields.
It is worth noting that these two fields are always in phase and perpendicular to each other.
Light is just one part of the electromagnetic spectrum, the part that our eyes can see (400nm (violet) – 700nm (red))

Question 2

Velocity of light in vacuum

Answer 2

The speed of light in vacuum is equal to ≈ 300 000 km/s and can be obtained from the following equation:

𝑐 = 1/sqrt(𝜀0* 𝜇0)

where 𝜀r is the vacuum electric permittivity and 𝜇r is the vacuum magnetic permeability. In order to find the speed of light in a different medium, it is necessary to modify the above equation by including relative permittivity and relative permeability.

𝑐 = 1/sqrt(𝜀0 * 𝜀r * 𝜇0 * 𝜇r)

Question 3

The Poynting vector

Answer 3

An electromagnetic wave can transport energy from one location to another. The magnitude and direction of the energy flow is described in terms of a vector S called the Poynting vector S [W/m^2]

𝑆 = 1/𝜇0 * 𝐸×𝐵

𝜇0 is the permeability of the medium through which the radiation passes, E is the amplitude of the electric field and B is the amplitude of the magnetic field.