Homework Question 1A.3

[chrisavalos-2L]

Which of the following happens when the frequency of electromagnetic radiation decreases? Explain your reasoning
(a) the speed of radiation decreases
(b)the wavelength of 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 got the answer of (a) I was wondering if this was the right answer and if so, I do not know how to explain why this is right?

[almaochoa2D]

The answer is actually c. The extent of change is referring to the slope of the wave so when the frequency decreases the wave gets wider which means that the extent of change is decreases.

[Jewelyana3A]

So, just to break it down for you... If you look at (a) you’ll notice that this can’t be the answer because speed is constant. The speed of the radiation wouldn’t decrease. For (b) the wavelength of the radiation wouldn’t decrease since frequency and wavelength are inversely proportional. (D) isn’t the answer either because energy and frequency are proportional. So energy wouldn’t increase as the frequency decreases. So, now looking at (c) we see that the extent of the change in the electrical field at a given point decreases. This is true because As the frequency of the electromagnetic radiation decreases the waves will widen out and the slope of the wave decreases.

[Michelle Nwufo 2G]

So, just to break it down for you... If you look at (a) you’ll notice that this can’t be the answer because speed is constant. The speed of the radiation wouldn’t decrease. For (b) the wavelength of the radiation wouldn’t decrease since frequency and wavelength are inversely proportional. (D) isn’t the answer either because energy and frequency are proportional. So energy wouldn’t increase as the frequency decreases. So, now looking at (c) we see that the extent of the change in the electrical field at a given point decreases. This is true because As the frequency of the electromagnetic radiation decreases the waves will widen out and the slope of the wave decreases.

Can you further explain what you mean by speed being a constant. How does speed being a constant affect its ability to decrease as a result of the frequency of the radiation decreasing? Do you mean that the speed is a fixed value?

[davidbakalov_lec2_2L]

All electromagnetic waves travel at the speed of light 'c', hence the equation c = wavelength * frequency. Because frequency and wavelength are inversely proportional to each other, a decrease in frequency will affect the wavelength but not the speed - which is a constant.