do em waves decrease in amplitude or lose energy in free space as they move with time?

Question

Why? Why?

Answer 1

If the wave is spherical such as that emitted by an ordinary star it spreads out like a sphere and obeys the inverse square law and its intensity decreases as such. This is simply due to the geometry of space and the type of wave.

If it is directional such as a radio beam, then the amplitude does not decay appreciably. We are still receiving signals from the Voyager spacecraft which has left our solar system. Also some stars like pulsars send out light in a directional beam which does not diminish much. So as long as the wave does not spread out then it does not diminish in amplitude but this is almost impossible in the real world.

The energy of a wave is proportion to the square of the amplitude.

E prop to A^2

For instance, the beam of a laser has a spread, though much smaller than an ordinary source of light, and would look conical, obeying the inverse squsre law.

Answer 2

In free space, electromagnetic waves would not lose any energy because there is nothing to which it can impart any energy. However, the energy being carried by the wave is being spread over a larger area as the waves travel further.

The area over which the waves are spreading is a sphere (or some portion of a sphere, bounded by the same radii) so the area covered by the energy in the wave is proportional to the square of the distance travelled. And the strength is proportional to the 1 / the area. Hence, the inverse square law.

Answer 3

EM waves if suffer attenuation with distance , they're
undetectable on the earth's surface , then ,there are three
possible cases : (1) amplitude of far distant field increase
wchich is impractical
(2) amplitude decrease, which means they are undetectable
from ther emitting source
(3) amplitude of periodic nature , which is the actual case

so , waves are a form of electromagnetic energy with double periodicity in time and space

any further details , refer to my mail
([e-mail])

Answer 4

Yes. The amplitude decreases.

No. They don't lose energy.

Answer 5

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Answer 6

Yes... But clarify...

Are you asking:
Is attenuation of electromagnetic waves a function of transversing space-time?

Or are you asking:
Will attenuation occur when electromagnetic waves travel through a partial vacuum?

The answer to both is yes...

Answer 7

yes.
For example light from far away stars is very faint but much stronger from our star (the sun).

Answer 8

yes

Answer 9

wow, let me know when you find out.

Answer 10

no