# Period for electromagnetic waves

• convict11
In summary, wavelength is the distance between two waves traveling along the same direction and period is the time it takes for one wave to complete one oscillation. Frequency is the number of waves that pass by in a second. The speed of light in a medium is the speed of light in that medium divided by the index of refraction.
convict11
Hi, I have a couple of questions here I am having a little bit of difficulty with.

1) What is the wavelength of an X-ray that has a period of 1.30x10e-10s?

2) A certian EMR has a wavelength of 2.14x10e-5m in air. What is the wavelength is water(n = 1.33)?

I am not looking for the answers as I prefer to be able to understand the questions and how the answers are correct but I have searched the the textbook on this unit about magnetic fields and electric fields but can not find anything of wavelengths and periods. If anyone could tell me the equation to use or anything it would be great

All I know is that Speed of wave = Frequency * Wavelength

Is the period the frequency? and the speed of wave would be the speed of light?

convict11 said:
Is the period the frequency?
Almost. The frequency is how many oscillations the wave goes through in a second. The period is the time it takes the wave to complete one oscillation. A little proportionality relation shows that

$$\frac{f}{1s}=\frac{1}{T}$$

where T is the period, and f the frequency.

convict11 said:
and the speed of wave would be the speed of light?
Yes, but the speed of light varies depending on the medium it travels in. You ought be have a formula relating speed of light of wavelenght as a function of the refractive index n somewhere in your notes or book.

In order to understand some of the methods of solving the questions you asked, it is often very helpful to do a unit analysis on a piece of paper. If you know the units of certain variables (e.g. frequency, period, etc) it is often very simple to see the relationship. For instance, if you know the frequency is in the units [1/s] and that period is in the units , it's easy to see that there's an inverse relationship.

You noted that $v=f\lambda$. If you do a unit analysis on that, you see that you will get $[m/s]=[1/s][m]$, an the units work out to equal each other. If you're ever stumped as to how an equaton should look, or which variables you might need to use, or you have a question along the lines of "is the period the frequency," a unit analysis can often provide a quick and easy answer.

In response to your second problem, you have an index of refraction n. n is defined as the ratio of the speed of light in vacuum to the speed of light in the medium in question. In this case, the speed of light in vacuum is 1.33 times faster than the speed of light in the medium. This essentially means that all of the waves will propogate at c/1.33 through the medium, and therefore the wavelengths will also be that much smaller. It's a simple multiplication/division factor on $\lambda$

Thanks a lot

Thanks for the reply's guys

## 1. What is the period of an electromagnetic wave?

The period of an electromagnetic wave is the amount of time it takes for one complete cycle of the wave to occur. It is typically measured in seconds.

## 2. How is the period of an electromagnetic wave related to its frequency?

The period and frequency of an electromagnetic wave are inversely related. This means that as the frequency increases, the period decreases and vice versa. This relationship is described by the equation: T = 1/f, where T is the period and f is the frequency.

## 3. How does the period of an electromagnetic wave affect its energy?

The period of an electromagnetic wave does not directly affect its energy. The energy of an electromagnetic wave is determined by its amplitude, which is the height of the wave's crests. However, the period does play a role in determining the wavelength of the wave, which can indirectly affect its energy.

## 4. Can the period of an electromagnetic wave be changed?

The period of an electromagnetic wave is determined by its source and cannot be changed. However, the speed of the wave can be affected by the medium through which it is traveling, which can in turn affect its period.

## 5. How is the period of an electromagnetic wave related to the speed of light?

The speed of light is directly related to the period of an electromagnetic wave. This relationship is described by the equation: c = λ/T, where c is the speed of light, λ is the wavelength, and T is the period. As the speed of light is a constant, any changes in wavelength or period will affect the other variable accordingly.

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