• Lord33
In summary, the wave values are the same for a mobile phone or radio wave. The frequency is different, but the wave shape is the same.
Lord33

## Homework Statement

Flat harmonic electromagnetic wave propagates in the positive direction in vacuo axis y. Vector electromagnetic energy flux density is given by: S(y,t)=Sm *cos(wt-ky)2.Wave value: k=(2*π)/λ=0.41 m-1,Amplitude Sm=26 W/m2.Compare this wave with another wave.

ƒ=V/λ
k=(2*π)/λ
E=h*ƒ

## The Attempt at a Solution

I find wavelenght from wave value λ=15m ⇒ it is a radio short wave ⇒next i find frequency from ƒ=V/λ=2*107⇒and finally i find photon energy E=h*ƒ=1,3*10-26 J =81*10-9neV.

I compared the result with the table, and he enters the period of short radio waves, ie, this wave is the same radio signal from your phone or radio?Maybe I made a mistake somewhere?

Radio or Mobile phone waves are not flat (I suppose you mean plane waves by the term flat) but they are spherical waves.In order to be more accurate, they are not even spherical waves but they resemble spherical waves when we are far away from the source antenna that produces the waves, they resemble spherical waves in the far field region as we say.

In real world we cannot produce plane(flat) waves cause they would require infinite amount of energy. We can produce spatially restricted plane waves inside waveguides https://en.wikipedia.org/wiki/Waveguide_(electromagnetism).

Last edited:
Lord33
What about the amplitude, how do I compare with short waves? If ampiluda will be 1026?

Lord33 said:
What about the amplitude, how do I compare with short waves? If ampiluda will be 1026?
It doesn't matter what the amplitude is, we look only at the frequency (or equivalently the wave length) if we want to check whether it is a short wave or VHF/UHF wave or a microwave etc. Your calculations seem correct to me.

In my previous post I just wanted to say that plane waves (regardless of their frequency) are not physically realizable, unless of course they are restricted inside waveguides.

Lord33
Delta² said:
It doesn't matter what the amplitude is, we look only at the frequency (or equivalently the wave length) if we want to check whether it is a short wave or VHF/UHF wave or a microwave etc. Your calculations seem correct to me.

In my previous post I just wanted to say that plane waves (regardless of their frequency) are not physically realizable, unless of course they are restricted inside waveguides.

At any significant distance from the transmitter the radiation is indistinguishable from a plane wave. For example at a 1 m antenna located just 1 km from the transmitter the curvature of the wave over the length of the antenna is 125 microns or less than 1e-8 of the wavelength. Why confuse the issue with this?

Cutter Ketch said:
At any significant distance from the transmitter the radiation is indistinguishable from a plane wave. For example at a 1 m antenna located just 1 km from the transmitter the curvature of the wave over the length of the antenna is 125 microns or less than 1e-8 of the wavelength. Why confuse the issue with this?

For two reasons
1) Its good to be accurate even though the difference in real world might be small in the case you display(which it isn't in this case if you take into account point 2) see below)
2) You are "hiding" the fact that in plane waves the amplitude is constant, while in spherical waves the amplitude is inversely proportional from the distance from the source. That's why spherical waves require finite amount of energy, while plane waves require infinite energy.

Short wave radio and phone/radio use different frequency bands to transmit signals. Short wave radio uses frequencies between 1.6 and 30 MHz, while phone/radio uses frequencies between 30 and 300 MHz. This difference in frequency allows short wave radio signals to travel longer distances, but with lower quality compared to phone/radio signals.

## Which type of radio wave is more commonly used for international broadcasting?

Short wave radio is more commonly used for international broadcasting due to its ability to travel long distances. It is also less susceptible to interference from weather and other obstacles.

## How do short wave radio and phone/radio differ in terms of signal strength and quality?

Short wave radio signals have lower strength and quality compared to phone/radio signals. This is because short wave signals are more prone to atmospheric and electrical interference, while phone/radio signals are less affected by these factors.

No, short wave radio signals cannot be received on phone/radio devices. These devices are designed to receive signals within the 30-300 MHz frequency range, while short wave radio signals are outside of this range.

Phone/radio signals are generally more reliable and have better sound quality compared to short wave radio signals. Additionally, phone/radio devices are more widely available and easier to use compared to short wave radios, making them more convenient for everyday use.

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