Question 1.A.3


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Amir Bayat
Posts: 115
Joined: Sat Sep 07, 2019 12:16 am

Question 1.A.3

Postby Amir Bayat » Thu Oct 10, 2019 1:27 pm

The question states:

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.

The correct answer is C. I understand how the answer cannot be A,B, or C, but how is the answer C? Is this due to the change in area of the electric field? Is there a formula explaining this?

Joanne Lee 1J
Posts: 100
Joined: Thu Jul 25, 2019 12:15 am

Re: Question 1.A.3

Postby Joanne Lee 1J » Thu Oct 10, 2019 1:48 pm

The extent of the change in the electrical field is referring to the slope of the waves and so as the frequency decreases, the waves of would be broader and more spread out, therefore meaning that the slopes of the waves would be less steep. This decrease in the slope means that the extent of the change in the electrical field would be decreasing as frequency decreases. To my knowledge, there is not formula explaining this concept.

Joseph Saba
Posts: 154
Joined: Thu Jul 11, 2019 12:16 am

Re: Question 1.A.3

Postby Joseph Saba » Thu Oct 10, 2019 1:50 pm

I also used the process of elimination on this problem. You can calculate and reason out all of the other responses other than part C.

Anthony Hatashita 4H
Posts: 103
Joined: Wed Sep 18, 2019 12:21 am

Re: Question 1.A.3

Postby Anthony Hatashita 4H » Thu Oct 10, 2019 4:17 pm

As I first did this problem I immediately looked for a "the wavelength increases" answer, but there was none. I also used the process of elimination to eliminate a b and d, leaving only c as the possible answer. From the correct answer you can learn that higher wavelength results in less change in the electrical field at any point.

Alexa Mugol 3I
Posts: 54
Joined: Sat Aug 17, 2019 12:17 am

Re: Question 1.A.3

Postby Alexa Mugol 3I » Thu Oct 10, 2019 9:02 pm

I was confused about this too. If you look at Figure 1A.7 in the text, it says that "the electric field of electromagnetic radiation oscillates in space and time" (referring to the oscillating waves in the radiation). So, I think when C says "extent of change in the electrical field," it's referring to the oscillation. Therefore, since the frequency is decreased, it means less oscillation in the waves (or broader waves as someone had mentioned earlier). If the frequency was increased, you would see more oscillation and shorter, smaller waves.


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