Why do radio waves spread out while higher frequency waves travel in beams? Why is it that radio w

babyagelesszj 2022-07-04 Answered
Why do radio waves spread out while higher frequency waves travel in beams?
Why is it that radio waves spread out in proportion to the square of the distance, while higher frequency electromagnetic waves, like microwaves, infrared waves, light, etc are able to propagate as beams? What fundamental property allows higher energy waves to travel differently than lower energy?
You can still ask an expert for help

Expert Community at Your Service

  • Live experts 24/7
  • Questions are typically answered in as fast as 30 minutes
  • Personalized clear answers
Learn more

Solve your problem for the price of one coffee

  • Available 24/7
  • Math expert for every subject
  • Pay only if we can solve it
Ask Question

Answers (2)

Hayley Mccarthy
Answered 2022-07-05 Author has 19 answers
Due to diffraction, wave effects become more important as the size of the wave source becomes comparable to the length of the wave. Visible light has micrometer-scale wavelengths, so a millimeter-sized light source is thousands of wavelengths across and diffraction isn't a very big deal. But radio wavelengths can be many meters, producing similar collimation for a radio "beam" would require an emitting antenna hundreds or thousands of kilometers across.
You can use the same logic to think about shadows. A hair that's less than a millimeter across can cast a well-defined shadow, while radio waves diffract around buildings. However larger objects can cast well-defined radio shadows: for instance astrophysical radio sources disappear when they are covered by the Moon or the Sun, which are both very many wavelengths across.
Note that even "collimated" light undergoes dispersion. Any sort of focusing optical system will produce a beam waist at some finite distance from the final focusing element (mirror or lens or whatever); beyond that beam waist the intensity of the light falls off like r 2 just as if a light source were at that location. A perfectly collimated beam of light is prohibited by the uncertainty principle, unless the beam is infinitely wide.

We have step-by-step solutions for your answer!

kramberol
Answered 2022-07-06 Author has 5 answers
They all spread out, but generally speaking the directivity of an antenna or emitter (assuming optimal design) is proportional to its volume, in wavelengths cubed. So a tiny high-frequency antenna with a volume of five wavelengths cubed has the same directivity as a huge low-frequency antenna also with a volume of five wavelengths cubed. Of course, other things also affect directivity, like temperature, the particular antenna design, etc. That's why I said "generally speaking".

We have step-by-step solutions for your answer!

Expert Community at Your Service

  • Live experts 24/7
  • Questions are typically answered in as fast as 30 minutes
  • Personalized clear answers
Learn more

You might be interested in

asked 2022-07-10
Spread and direction of the cosmic background radiation
Something I can never understand is that where the cosmic background radiation spreads?
If I know well, the cosmic background radiation is actually the light of the Big Bang. If it happened exactly in the same time, it must have spread into the theoretic center of the universe. Which would mean that it already reached every parts of it, in case if it happened in the same time with the Big Bang.
It be possible that it spreads to this direction, but universe expands faster. In this case, the radiation approaches but also moves off - just like everything in the universe. But it's possible only if the universe expands faster than the speed of light. Is this possible?
If it would spread to the direction of the "edge" of the universe, we shouldn't be able to know about its existence, because it would never reach us.
Also, these theories are true with an important conclusion: universe has a beginning in time, which means that once upon a time, it started to expand - consequently it must have a size limit. The reason is that universe has 4 dimensions: length, width, height, and time. One of them (time) is not infinite, so none of the others can be infinite.
asked 2022-06-14
Why do wave packets spread out over time?
Why do wave functions spread out over time? Where in the math does quantum mechanics state this? As far as I've seen, the waves are not required to spread, and what does this mean if they do?
asked 2022-06-07
Variational wavefunctions and "spread" of potential in quantum mechanics
A particle in a box has an energy that decreases with the size of the box. In the general case, it is often said that a variational solution for a "narrow and deep" potential is higher in energy than a variational solution for a "wider and shallower" potential, by appealing to the particle in a box as a special case. The former wavefunction is said to be "more confined" in the former than the latter, and the act of being given more space to spread out is said to lower the energy variationally.
Question: are there rigorous mathematical statements of this argument?
asked 2022-07-02
How can the energy of a magnetic field spread at speed of light?
I would like to solve one question. Suppose that we have a point charge. Then we apply a force on it, and as it accelerates, it emits electromagnetic waves and is pushed back due to Abraham-Lorentz force. But then, when we drop it and it moves at constant speed, it starts to create a magnetic field that spreads at speed of light. So as the field occupies more volume, it increases its energy but we are not giving any energy as we have dropped it. So, where does this energy come from?
asked 2022-07-07
Do cracks in solids spread at a characteristic speed?
I have a feeling this is actually a pretty complicated problem in detail as I know a tremendous amount of research is done on the behavior of materials under stress, and I think the way materials fracture/crack is a useful diagnostic tool.
As a starting point, waves travel at the speed of sound in a material, which is to say they are mechanical waves. Do cracks also propagate at the speed of sound?
Another related question is, do the cracks in a solid move at a constant speed? Obviously it is possible for a crack to form and stop propagating, so this might imply a dissipation of some vibrational amplitude until the energy is below the point of being able to break bonds/fragment atoms (sheets for some solids). It also might imply that the crack does not behave like a wave and spreads at a non-constant speed. Which is right?
Lastly, do all solids follow the same rules for the speed at which they fracture? I'm thinking of glass, which probably is not a good place to start on this question because it is an amorphous solid (some people say incredibly viscous liquid but this feels like semantics). Obviously some glass will crack into large pieces and some will fracture like a spiderweb. Are these processes fundamentally the same but with different microscopic details? And how does fracturing in glass relate to something simpler like the breaking of a single atom solid? I haven't seen this happen, but surely it is possible.
Obviously there were quite a few question there, but they were only meant to give a general idea of the types of questions would be nice to have answered. Maybe the question is actually quite simple and one answer will suffice, or maybe it's complicated and there are multiple good answers.
asked 2022-05-13
Does gas spread out equally everywhere?
"Gases can fill a container of any size or shape. It doesn't even matter how big the container is. The molecules still spread out to fill the whole space equally. That is one of their physical characteristics."
If a fixed quantity of gas is let out in a limited space, will it spread out equally and maintain a fixed gas distribution throughout the space?
Or, does it go where the gravitational pull is maximum? And what factors affect the distribution of gas in a given area?
asked 2022-05-07
Why do electrons in a current spread apart, from their point of view?
There are many videos explaining how special relativity causes magnetism, with the most relevant part being that from the reference frame of the electrons, the positively charged ions in the wire have gotten closer together, and the negatively charged electrons have spread apart, a non-zero electric charge in a wire. We can determine that this must happen using the fact that in a lab reference frame, the wire is electrically neutral, and applying a Lorentz transformation to the electrons and ions. However, the electrons must see a different mechanism causing the space between them to increase. They need to see something pushing them apart. They don't know that the wire needs be electrically neutral in another reference frame. What's this mechanism that they see? Does it have anything to do with the period of time when they're accelerating?
I saw a bunch of questions that seemed similar to this one, but I didn't find any of the answers to be satisfactory. They all seemed to just explain how we know that the wire must be charged in different reference frames, using the Lorentz tranformation.

New questions