Textbook Problem 1A.3

$E=hv$

SophiaNguyen_2E
Posts: 50
Joined: Wed Sep 30, 2020 9:59 pm

Textbook Problem 1A.3

Hello! So the question is:

Which of the following happens when the frequency of electromagnetic radiation decreases? Explain your reasoning.
(a) The speed of the radiation decreases.
(b) The wavelength of the radiation decreases.
(c) The extent of the change in the electrical field at a given point decreases.
(d) The energy of the radiation increases.

I'm pretty sure the right answer is C, but I wanted to understand why A isn't the right answer. Can someone explain the relationship between the speed of radiation and frequency/wavelength? Thank you in advance!

Posts: 42
Joined: Wed Sep 30, 2020 9:31 pm

Re: Textbook Problem 1A.3

I am fairly certain that there is no relationship between the frequency/wavelength of electromagnetic radiation, and the speed at which it moves. This is because electromagnetic radiation moves at a constant speed of 3.0 x 10^8 m/s in a vacuum. This is how we get the formula c= wavelength * frequency.

Kyla Roche 2D
Posts: 47
Joined: Wed Sep 30, 2020 9:59 pm

Re: Textbook Problem 1A.3

Frequency has a direct relationship with Energy however not with speed because speed if a constant (c)

Daniela_Martinez_3B
Posts: 43
Joined: Wed Sep 30, 2020 9:47 pm

Re: Textbook Problem 1A.3

Any electromagnetic wave's frequency multiplied by its wavelength equals the speed of light. The speed of light is always 3x10^8!

Tae Pasawat 2A
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Joined: Tue Oct 06, 2020 12:16 am

Re: Textbook Problem 1A.3

Can someone please explain part C? Thank you!

Megan Lu 3B
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Joined: Wed Sep 30, 2020 9:49 pm

Re: Textbook Problem 1A.3

^ Hi! I believe the correct answer should be C because frequency in EM radiation refers to the number of cycles that occur within a given amount of time. If the frequency decreases, there are fewer cycles taking place in this interval of time and the waves broaden. Thus, the extent of change that happens decreases. Hope this makes sense.

Veeda Khan 2E
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Joined: Wed Sep 30, 2020 10:00 pm

Re: Textbook Problem 1A.3

Tae Pasawat 2A wrote:Can someone please explain part C? Thank you!

Another way to think of it is that the peaks of the waves are further apart, so the "slope" of the waves are less, thus a decrease of change between points.

Edwin Liang 2I
Posts: 40
Joined: Wed Sep 30, 2020 9:34 pm

Re: Textbook Problem 1A.3

Since frequency and wavelength are directly related to one another( c = λ * v ), the slope on a wave with high frequency will be more than that with a lower frequency. This means the "extent of change" (slope) decreases as frequency decreases.

jasmineculilap_2J
Posts: 40
Joined: Wed Sep 30, 2020 9:40 pm

Re: Textbook Problem 1A.3

Speed of light in a vacuum is constant where c = 3.00 * 10^8. c can also be found by c = λ * v, so frequency and wavelength are inversely related.

KKrivenko_3J
Posts: 58
Joined: Wed Sep 30, 2020 9:52 pm
Been upvoted: 1 time

Re: Textbook Problem 1A.3

Choice A isn't the right answer because the speed of radiation is always constant and equal to the speed of light ($2.99*10^{8}$ m/s). Therefore, as frequency decreases, the wavelength increases, so that their product would always be equal to the speed of light. Hope this helps :)