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### 1.3 manipulating light equations

Posted: **Wed Sep 30, 2015 10:11 pm**

by **Cindy Ma 1B**

Which of the following happens when the frequency of electromagnetic radiation decreases?

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.

My first thought for this question was to refer to the equation E=hv (thats frequency, but I don't know how to type the actual symbol), but if the energy is related to the frequency, shouldn't the change be a decrease in energy? It sounds like the answer (c), but I'm not sure what (c) is referring to.

### Re: 1.3 manipulating light equations

Posted: **Wed Sep 30, 2015 10:25 pm**

by **Andrew Kolodziej 1C**

The answer is C by the way. A change in the electrical field is a fancier term for saying that the frequency decreases. These electric fields that are part of the Electromagnetic Radiation push on particles in a given field. This "push" causes the particles to oscillate. Oscillation is the change in direction and strength, and this can be expressed as a unit frequency. For example the electric field oscillates at 6.4x10^14 Hz. So by saying that the electric field decreases, they are saying that the frequency goes down as well. Hopefully this helped.

### Re: 1.3 manipulating light equations

Posted: **Wed Sep 30, 2015 11:45 pm**

by **304621080**

The best way about focusing on this question is thinking about it in terms of the slope. As the frequency decreases, so does the extent of the change because the wave elongates creating a decrease in the slope. With respect to energy, if you combine the equation E=hv(v being frequency) and c=wavelength*v(v being frequency) you get E=hc/wavelength proving that energy and wavelength are inversely proportional.

### Re: 1.3 manipulating light equations

Posted: **Fri Oct 02, 2015 11:02 am**

by **Emily Chu 3E**

Similar to what was said above, if you look at the equation c = λv (v as in frequency), then when frequency is decreasing, the wavelength must be increasing in order for c to be a constant. Since the wavelength is increased/elongated, it has a smaller slope and therefore a decrease in the extent of change at any given point.