Electromagnetic wave radiation

Содержание и основные понятия

Accelerated moving charges create a variable electromagnetic field that can separate itself from the source. Antenna converts high frequency current into wave and back.
GEF · 11 grade
PIF · Baseline
Interactive model
antenna
radiation
polarization
intensity
01
The physical picture
What happens and what boundaries the model has.
Main message
Accelerated moving charges create a variable electromagnetic field that can separate itself from the source. Antenna converts high frequency current into wave and back.
Permanent current doesn't create continuous wave radiation.
The antenna size will be aligned with the wave length.
The intensity away from the point source is lost about 1/r2.
How to reason
First, name the system and the interaction, then select the values, and only then write down the law. The formula works within the model's assumptions.
02
Laws and values
Symbols should be read as a relationship of values, not as a recipe for substitution.
c
=
λ
ν
c=\lambda\nu
c
=
λ
ν
Wave speed
I
=
P
4
π
r
2
I=\frac{P}{4\pi r^2}
I
=
4
π
r
2
P
​
intensity
Review of the situation
The doubling of the distance from the isotropic transmitter reduces the density of the energy flow by about four times.
04
Links and application
In the real world
The doubling of the distance from the isotropic transmitter reduces the density of the energy flow by about four times.
Model verification
Compare the prediction with observation, evaluate the units, the order of magnitude and the influence of the factors not taken into account. Disparity does not always mean an error of law: often idealization is no longer sufficient.
C
What needs to be understood
Outcome 1
To explain the physical meaning of the topic "Eradiation of electromagnetic waves" through the model, not just through the formula.
Outcome 2
Distinguish and correctly use terms: antenna, radiation, polarization.
Outcome 3
Indicate the conditions for the applicability of the law, verify units and limit cases.
T
Terms of the topic
The definition should indicate the physical meaning, not a substitute for a domestic synonym.
antenna
A device that converts electromagnetic waves into an electrical signal or reverses it.
radiation
Transport of energy by electromagnetic waves; does not require a material environment.
polarization
Streamlining the orientation of cross-wave fluctuations.
intensity
Energy transported by wave per unit of time through a single site perpendicular to the direction of proliferation.
F
Origin and conclusion of the formulas
The fundamental law cannot be "proven" by algebras: for each record, it is stated whether it is a definition, an experimental law, or a model effect.
c
=
λ
ν
c=\lambda\nu
c
=
λ
ν
model effect
The speed of the wave.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
T
=
1
ν
T=\frac{1}{\nu}
T
=
ν
1
​
In one period, the T source fluctuates once.
λ
=
c
T
\lambda=cT
λ
=
c
T
During this time, the electromagnetic wave front in the vacuum passes one wave length.
c
=
λ
T
=
λ
ν
c=\frac{\lambda}{T}=\lambda\nu
c
=
T
λ
​
=
λ
ν
The exclusion of the period links speed, wave length and frequency.
Conditions:
Monochromatic electromagnetic wave in the vacuum; in environment, instead of c, phase v of the frequency is used.
Monitoring:
The dimensions of both parts shall coincide; the result shall be checked for sign, order and limit case.
I
=
P
4
π
r
2
I=\frac{P}{4\pi r^2}
I
=
4
π
r
2
P
​
model effect
Intensity.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
I
:
=
P
S
I:=\frac{P}{S}
I
:=
S
P
​
Intensity is defined as the capacity per unit of area perpendicular to the energy flow.
S
сф
=
4
π
r
2
S_{\text{сф}}=4\pi r^2
S
cf
​
=
4
π
r
2
In the isotropic point source, the power is distributed along the radius of r.
I
=
P
4
π
r
2
I=\frac{P}{4\pi r^2}
I
=
4
π
r
2
P
​
Maintaining full power gives the law of backward squares.
Conditions:
Isotropic point source in a homogeneous non-absorbing environment, long-range zone; P is the total radiated power.
Monitoring:
The dimensions of both parts shall coincide; the result shall be checked for sign, order and limit case.
!
Model boundaries and typical errors
Error: Forget model condition
You can't put the formula on any situation just because it's a coincidence of letters. The key condition of this topic is that constant current doesn't create continuous wave radiation.
How to Check the Mind
The antenna size is aligned with the wave length. Then check the unit, vector direction and result behaviour at zero or very large parameter.
Σ
Conclusion on the topic
Electromagnetic wave radiation
Accelerated moving charges create a variable electromagnetic field that can separate itself from the source. Antenna converts high frequency current into wave and back.
Permanent current doesn't create continuous wave radiation.
The antenna size will be aligned with the wave length.
Any numerical result shall be accompanied by a unit, a sign and an explanation of its physical meaning.
The content is consistent with the FRP on Physics of the OS/OSS 2025 and the subject matter of the current lines of the PNP: I. M. Peryškin and co-authors (7–9), G. J. Mäkishev and coauthors (10–11), and with the lines "Engineers of the Future" and V. A. Kasyanov. The original texts are not reproduced, the text of the textbooks is not reproduced.