# The Naked Scientists Forum

### Author Topic: Electomagnetic Waves  (Read 2825 times)

#### sohail

• Jr. Member
• Posts: 23
##### Electomagnetic Waves
« on: 12/09/2007 19:52:48 »
If for instance, electromagnetic waves come in quantum "lumps" how come electormagnetic waves have an infinite range?

#### lightarrow

• Neilep Level Member
• Posts: 4586
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##### Electomagnetic Waves
« Reply #1 on: 12/09/2007 20:18:03 »
If for instance, electromagnetic waves come in quantum "lumps" how come electormagnetic waves have an infinite range?
"lumps" are referred to energy.

#### JP

• Neilep Level Member
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##### Electomagnetic Waves
« Reply #2 on: 12/09/2007 21:05:25 »
Electromagnetic waves don't have infinite range.  The source generating the wave has to be turned on at some point.  When the source is turned on the wave will start moving away from it at the speed of light, so its range is determined by how long the source has been turned on multiplied by the speed of light.

#### another_someone

• Guest
##### Electomagnetic Waves
« Reply #3 on: 12/09/2007 22:26:19 »
Electromagnetic waves don't have infinite range.  The source generating the wave has to be turned on at some point.  When the source is turned on the wave will start moving away from it at the speed of light, so its range is determined by how long the source has been turned on multiplied by the speed of light.

Range and speed are separate issues.

A Boeing 747-100 may have a range of over 8,000 miles, but this implicitly assumes it has the time to achieve that range.  The aircraft has, like an electromagnetic wave, a limited speed, so if one applies a time constraint to your notion of range, then the 8,000 mile supposed range may never be achieved; but implicit in the notion of range is that time is not a constraint.

#### sohail

• Jr. Member
• Posts: 23
##### Electomagnetic Waves
« Reply #4 on: 13/09/2007 00:07:21 »
I was just thinking that the energy gradually dissapates and that if the energy is lost (or gained) in discrete amounts then surely the range of the radiation is finite?

And a little off the subject:
If electromagnetic waves (or anything for that matter) travels at the speed of light couldn't they be in several places at the same time as time effectively stops for them?

#### another_someone

• Guest
##### Electomagnetic Waves
« Reply #5 on: 13/09/2007 00:16:37 »
I was just thinking that the energy gradually dissapates and that if the energy is lost (or gained) in discrete amounts then surely the range of the radiation is finite?

The energy of EM is not lost or gained (unless it interacts with matter), it is merely smeared over a wader area.

And a little off the subject:
If electromagnetic waves (or anything for that matter) travels at the speed of light couldn't they be in several places at the same time as time effectively stops for them?

It may stop for them, but not for use viewing them (since we cannot travel at their speed is it not practical to think in terms of time elapsed from the perspective of a photon - time elapsed only means something if something changes, so a neutron that lasts for a limited time before decaying into a proton and electron is concerned about time, but a photon never decays, so elapsed time has no meaning).

#### The Naked Scientists Forum

##### Electomagnetic Waves
« Reply #5 on: 13/09/2007 00:16:37 »