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### 1.3

Posted: Sat Oct 14, 2017 10:32 pm
I understand most of this question, but I am a little confused on choice c which says "the extent of the change in the electrical field at a given point decreases". The answer key says the electrical field corresponds to amplitude, but how exactly are they related?

### Re: 1.3

Posted: Sat Oct 14, 2017 10:37 pm
I was confused on this matter too The only way I was able to answer the question was process of elimination because I knew all the other ones were false. No sure why this one is true though. Can anyone please explain?

### Re: 1.3

Posted: Sun Oct 15, 2017 12:19 pm
From what I was told, since the frequency of electromagnetic radiation decreases, the wavelength of the radiation would increase because of the inverse relationship between wavelength and frequency. An increased (longer) wavelength of the radiation would cause a decreased amplitude, so the slope of the amplitude would be decreased as well. The extent of the change in the electrical field directly correlates with the slope of amplitude, so the extent of change in the electrical field would decrease as well. Hope this helps!

### Re: 1.3

Posted: Sun Oct 15, 2017 2:25 pm
For choice A, is the speed of the radiation a constant and that is how you know it cannot decrease? Or is there a way to determine the speed of the radiation? I understand why B and D are incorrect, but not sure about A. Also, I don't understand option C as well.

### Re: 1.3

Posted: Mon Oct 16, 2017 7:14 pm
I think that the speed of radiation is constant because they are light waves and the speed of light is a constant.

### Re: 1.3

Posted: Mon Oct 16, 2017 11:06 pm
This is what I wrote to explain choice c on another person's question about 1.3:

From the textbook:

Light is a form of electromagnetic radiation, which consists of oscillating (time-varying) electric and magnetic fields that travel through empty space at about 3 * 10^8 m/s, or at just over 670 million miles per hour. This speed is denoted c and called the speed of light. Visible light, radio waves, microwaves, and x-rays are all types of electromagnetic radiation. All these forms of radiation transfer energy from one region of space to another. The warmth we feel from the Sun is carried to us through space as electromagnetic radiation.
As a light ray passes an electron, its electric field pushes the electron first in one direction and then pulls it in the opposite direction, over and over again. That is, the field oscillates in both direction and strength (FIG. 1.7). The electric field of electromagnetic radiation oscillates in space and time.

Therefore I'm lead to believe the waves of electromagnetic radiation have the "electrical field" referred to in this question. When the frequency decreases, there are less wavelengths in the same amount of space, so the change or up-and-down motion of the wave is smaller per second.

As for part a), I think the speed of electromagnetic radiation is constant at the speed of light.