Textbook Problem 1A.3

[austinchun]

Hello! I was working through the textbook problems and was confused on one of the problems. It is question 1A 3 in The Quantum World section. Here is the problem:

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 visible radiation decreases.
(c) The extent of the change in the electrical field at a given point decreases.
(d) The energy of the radiation increases.

Can someone guide me through how to solve this problem. Thank you in advance!

[Sanjana Sivakumar 2E]

Hello!

For this question, the answer is C. For this, we need to understand that energy of a wave and electromagnetic radiation are synonyms. So, I basically remembered the equation of energy of a photon (which I guess can be considered as a type of wave - visible light) which is E = hv. Here we can see that if the frequency (v) decreases, the energy of the photon will also decrease (E). So they are directly proportional.


Hope this helps!

[Barbara Soliman 1G]

Hello! I was working through the textbook problems and was confused on one of the problems. It is question 1A 3 in The Quantum World section. Here is the problem:

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 visible radiation decreases.
(c) The extent of the change in the electrical field at a given point decreases.
(d) The energy of the radiation increases.

Can someone guide me through how to solve this problem. Thank you in advance!

We can use the process of elimination for this question. According to the equation for the speed of light, c= lambda*frequency. Since c is a constant (3.0*10⁸), when frequency decreases, that means wavelength has to increase and vice versa. Because of that we can rule out A and B. D would be incorrect according to E=hv, h is a constant (6.626*10^-34, so that means if frequency decreases, energy has to decrease as well. Thus, C is the right answer. Hope this helps!