The speed of an electromagnetic wave is equal to? a.the frequency of its motion or b.its wavelength in nm

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The speed of electromagnetic waves is a constant. It's equal to 3.0 x 10^8 m/s in a vacuum. since 1 meter is 10^9 nanometers, this would equal 3.0 x 10^17 nanometers per second. 

The relationship between speed, wavelength and frequency of waves is:

speed = frquency x wavelength

Since the speed of electromagnetic waves in a vacuum doesn't vary it would be more likely that you're being asked to calculate either the frequency or the wavelength. Rearranging the equation for speed, you get:

wavelength = speed/frquency

frequency = speed/wavelength

Light moves more slowly through substances than it does in a vacuum. In order to calculate the speed of light in a substance you need the index of refraction for the substance, which is the ratio og the speed of light in a vacuum to the speed of light in the substance.

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