There are two types of waves, mechanical and electromagnetic. Microwaves, infrared, and radio was are examples of electromagnetic waves. Which statement is true about the speed of an electromagnetic wave? A) It is not affected by changes in media.

B) It is slower in a vacuum than in a medium.

C) In a vacuum, its speed equals half the speed of light.

D) It slows down when it goes from a vacuum to a medium.

The answer is D.

Explanation:

One explanation I can give you is that generally waves travel faster through denser medium because the particles are tightly packed together and so they can transfer energy faster. But to verify the answer, I used Process of Elimination because the other 3 answers are not true. Choice A is entirely true, wave speed depends on the medium it is travelling through, so there is no way choice A is correct. Choice B is wrong because for example if we take light (an EM wave), it travels at a constant speed of 3.0x10^8 m/s in a vacuum and in open space. So, that proves that air or vacuum do not affect the speed of the wave in another medium. Choice C is related to Choice B, we just proved the speed of light is constant everywhere whereas choice C says that in a vacuum the speed is halved. Good luck in your Physics class and I hope for your best!