Textbook Question Number 1A 3 c

[Ian_Lee_1E]

The question asks, "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.

And the answer says:

(c) Yes. The electrical field corresponds to the amplitude; as the frequency decreases the waves broaden and the extent of the change(the slope of the wave) decreases.


I thought frequency does not have any relations with the amplitude of the wave. Amplitude just determines the brightness of the light or the loudness of the sound etc.

Why is this answer true?

[Kelly Singh]

If you think about the wave like a function on a graph, the "extent of change" would refer to the slope. A wave with a lower frequency would have a smaller slope, or extent of change, than a wave with a higher frequency. This question is definitely hard to visualize, but I hope this helps :)

[Charlene D 3H]

If you think about the wave like a function on a graph, the "extent of change" would refer to the slope. A wave with a lower frequency would have a smaller slope, or extent of change, than a wave with a higher frequency. This question is definitely hard to visualize, but I hope this helps :)

I was having trouble understanding this problem but your explanation made it a lot easier. I saw other explanations saying that extent of change refers to amplitude. Can this also be true?

[Andrew Wang 1C]

I saw other explanations saying that extent of change refers to amplitude. Can this also be true?

I don't think so, since the amplitude corresponds to the electric field. The extent of change refers to the slope from a trough to the next crest on the wave, or vice versa. So while changing the amplitude would affect the extent of change, amplitude itself is not the extent of change.