Relationship of intensity to frequency and power

[Tokspor]

For this question, you don't have to refer to the figure. I just included it in case anyone gets confused about the AC generator being mentioned in the question. I am actually wondering about the relationship between the intensity of a wave to its frequency and power.

Which of the following would increase the intensity of an EM wave emitted from the antenna?

A. Increasing the frequency of the AC generator
B. Increasing the period of the current in the antenna
C. Increasing the length of the antenna
D. Increasing the maximum voltage of the AC generator

The correct answer is D. Since P = Current*Voltage = Intensity/Area, increasing the voltage would increase the intensity. But why is A incorrect? I thought there is also the relationship that the intensity of a wave is proportional to the square of the frequency.

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[Isoprop]

For this question, you don't have to refer to the figure. I just included it in case anyone gets confused about the AC generator being mentioned in the question. I am actually wondering about the relationship between the intensity of a wave to its frequency and power.

Which of the following would increase the intensity of an EM wave emitted from the antenna?

A. Increasing the frequency of the AC generator
B. Increasing the period of the current in the antenna
C. Increasing the length of the antenna
D. Increasing the maximum voltage of the AC generator

The correct answer is D. Since P = Current*Voltage = Intensity/Area, increasing the voltage would increase the intensity. But why is A incorrect? I thought there is also the relationship that the intensity of a wave is proportional to the square of the frequency.

That relationship is for mechanical waves. EM is not a mechanical wave since it doesn't travel through a medium.

 

[premed101]

That relationship is for mechanical waves. EM is not a mechanical wave since it doesn't travel through a medium.

I believe it actually may be related, isopropyl.
Intensity=P/A=Energy/(time*area)
Energy of an EM wave=hf
Frequency is directly proportional to intensity...
I think this might be what is confusing. The equations seem to equate frequency and intensity.

 

[lDanny]

EM waves don't need a medium to travel, like they can travel in a vacuum.

and for the intensity, i think it is power= intensity*area not divide.

 

[Isoprop]

I believe it actually may be related, isopropyl.
Intensity=P/A=Energy/(time*area)
Energy of an EM wave=hf
Frequency is directly proportional to intensity...
I think this might be what is confusing. The equations seem to equate frequency and intensity.

E = hf is actually the energy of a photon. That is not the energy of a wave. And you are modeling intensity as a particle now, not a wave. That's okay, but you have to remember look at how frequency affects intensity. Intensity affected by how many photons hit an area and the energy per photon. While it may seem that increasing the frequency will increase the energy of each photon which would increase the intensity, that is not necessarily true because the number of photons can also decrease resulting in the same energy density.

The generator is creating a certain amount of energy per unit time. That energy is conserved and goes into the energy of the EM. From a photon perspective, we can either create a lot of little packets of low energy photons or create a small amount of large energy photons. The energy density is established by the source of energy which is the AC generator. That is why D is the credited response.