## Textbook Problem 1A. 3

$c=\lambda v$

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### Textbook Problem 1A. 3

In question 3 of focus topic IA, I understand why options A,B, and D are wrong. However, I do not understand why C is correct. I am confused about how the extent of change in the electrical field relates to EM radiation. What is the "extent of change" referring to in the question? The wording makes the answer difficult to understand.

Marley Magee 3A
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### Re: Textbook Problem 1A. 3

I'm not entirely certain that this will adequately answer your question, but I read an explanation for this and it turns out the electrical field is related to the amplitude of the EM radiation. So if the frequency has decreased then the wavelength has increased because of their inverse relationship, which also means that the width of the wave has gotten longer/broader. The slope of this curve, then, also decreases because the curve is not as steep, and slope is just rate of change so this implies that the "extent of change" of the electrical field over time has decreased.

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### Re: Textbook Problem 1A. 3

Juwan_Madaki_2B wrote:In question 3 of focus topic IA, I understand why options A,B, and D are wrong. However, I do not understand why C is correct. I am confused about how the extent of change in the electrical field relates to EM radiation. What is the "extent of change" referring to in the question? The wording makes the answer difficult to understand.

From my understanding, the context of "the extent of change" in this question refers to the direction of change (either increase or decrease) in the electrical field (represented by E in the equation E=hv). This equation shows that E, the energy per photon, is proportional to v because when multiplied by Plank's Constant (h) the frequency will yield the energy per photon. Therefore, as frequency decreases, energy decreases as well. The wording of this answer made the concept seem much more complex than it is. Hopefully this helps!

Juliet Carr 1F
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### Re: Textbook Problem 1A. 3

Similar to another response, I interpreted extent of change as relating to the amplitude and size/width of the wave. So, if frequency decreases, then wavelength has increased. Now within a certain region, the wave extends bigger than it did when the frequency was increased in this region. So, within this region the "extent of change" decreased. I thought of it like picking a point in the area under the curve, like in the region with one big wave there would be less change between two chosen points compared to if the frequency was increased to two waves in this same region, two points would have more of a change between each other. (Sorry this is kind of confusing and hard to explain, but if you draw it out it should make more sense visually).

Isaac Wen
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### Re: Textbook Problem 1A. 3

Juwan_Madaki_2B wrote:In question 3 of focus topic IA, I understand why options A,B, and D are wrong. However, I do not understand why C is correct. I am confused about how the extent of change in the electrical field relates to EM radiation. What is the "extent of change" referring to in the question? The wording makes the answer difficult to understand.

From my understanding, the context of "the extent of change" in this question refers to the direction of change (either increase or decrease) in the electrical field (represented by E in the equation E=hv). This equation shows that E, the energy per photon, is proportional to v because when multiplied by Plank's Constant (h) the frequency will yield the energy per photon. Therefore, as frequency decreases, energy decreases as well. The wording of this answer made the concept seem much more complex than it is. Hopefully this helps!

Hi Madison! Is there a way we can explain part C without using the E=hv? At least in part 1A, I thought we were focusing on the electromagnetic properties of light as a wave and not as a particle. Is there an explanation for "the extent of the change in the electrical field decreasing" using c=λν or simply by discussing the properties of electromagnetic waves?

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### Re: Textbook Problem 1A. 3

Isaac Wen wrote:
Juwan_Madaki_2B wrote:In question 3 of focus topic IA, I understand why options A,B, and D are wrong. However, I do not understand why C is correct. I am confused about how the extent of change in the electrical field relates to EM radiation. What is the "extent of change" referring to in the question? The wording makes the answer difficult to understand.

From my understanding, the context of "the extent of change" in this question refers to the direction of change (either increase or decrease) in the electrical field (represented by E in the equation E=hv). This equation shows that E, the energy per photon, is proportional to v because when multiplied by Plank's Constant (h) the frequency will yield the energy per photon. Therefore, as frequency decreases, energy decreases as well. The wording of this answer made the concept seem much more complex than it is. Hopefully this helps!

Hi Madison! Is there a way we can explain part C without using the E=hv? At least in part 1A, I thought we were focusing on the electromagnetic properties of light as a wave and not as a particle. Is there an explanation for "the extent of the change in the electrical field decreasing" using c=λν or simply by discussing the properties of electromagnetic waves?

I'm not sure if there is because the equation c=(lambda)v only shows the relationship between wavelength and frequency. If there is a way to explain it using that equation then I'm unaware of it so it might be a good question for a TA or UA.

reva_bajjuri
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### Re: Textbook Problem 1A. 3

could someone explain why d is wrong? i understand why c is correct but i thought the radiation of a wave was related to frequency because radiation/intensity was equal to the square of wavelength which is related to frequency? if this isnt true, what is the radiation of a wave proportional to?

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### Re: Textbook Problem 1A. 3

reva_bajjuri wrote:could someone explain why d is wrong? i understand why c is correct but i thought the radiation of a wave was related to frequency because radiation/intensity was equal to the square of wavelength which is related to frequency? if this isnt true, what is the radiation of a wave proportional to?

D is incorrect because frequency and energy are proportional. The question states that the frequency increases, therefore the energy would increase. The answer D states the energy would decrease implying an inverse relationship (which is incorrect).
Hope this helps!