Question Video: Identifying the Different Types of Electromagnetic Waves | Nagwa Question Video: Identifying the Different Types of Electromagnetic Waves | Nagwa

# Question Video: Identifying the Different Types of Electromagnetic Waves Physics • Second Year of Secondary School

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Which row of the table correctly shows how the wavelengths of various types of electromagnetic waves compare with each other?

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### Video Transcript

Which row of the table correctly shows how the wavelengths of various types of electromagnetic waves compare with each other?

In this question, we’re given a table. Each row of the table gives five different types of electromagnetic waves in a certain order. We need to work out which row of the table gives these waves in the correct order: from longest wavelength in the far left-hand column to shortest wavelength in the far right column.

Before we try and answer this question, let’s remind ourselves about the electromagnetic spectrum. As the name suggests, the electromagnetic spectrum is just a spectrum of different types of electromagnetic waves. The different types of electromagnetic wave are defined by their wavelengths. At one end of the spectrum, we have electromagnetic waves with very long wavelengths. And at the other end of the spectrum, the waves have very short wavelengths.

To help us understand this, we can sketch a wave that has a long wavelength at one end and a short wavelength at the other end. Notice how the wavelength decreases smoothly. There are no sudden changes or jumps, just a nice continuous wave. Then, we can divide this into regions, where each range of wavelengths corresponds to a different type of electromagnetic wave. Keep in mind that this wave is just a way of showing whether wavelengths are shorter or longer. In reality, the differences in wavelengths for these wave types will occur over several orders of magnitude, unlike this visual aid we are using. So, let’s now label these regions.

Recall that radio waves have the longest wavelength of any electromagnetic wave. Next, it’s microwaves, then infrared, then visible light, which contains all the colors we can see, then we have ultraviolet, and then X-rays. Finally, the type of wave with the shortest wavelength is 𝛾. Now we know how the wavelengths of the different types of electromagnetic waves compare, we can go back to the table given to us and see which row is correct.

Let’s start with row i. This row tells us that radio waves have the longest wavelength and 𝛾 rays have the shortest, which we know is correct. However, let’s look at these types in between. This row suggests that X-rays have a longer wavelength than visible light and that visible light has a longer wavelength than infrared. This is not correct. These three types are not in the correct order. So, we know row i cannot be the correct answer.

Now let’s look at row ii. Out of the five types of wave in this row, we know radio waves must have the longest wavelength because they have the longest wavelength of any electromagnetic wave. However, this row suggests that radio waves have shorter wavelengths than visible light, ultraviolet light, and X-rays. This is definitely not correct. This is enough for us to rule out row ii.

Row iii suggests that infrared waves have the longest wavelength of these types. Although we know that radio waves and microwaves have longer wavelengths, they are not included anywhere in this row. So, it is correct to say that of these types, infrared has the longest wavelength. This row also suggests that 𝛾 rays have the shortest wavelength, which we know is true. And these other three types — visible, ultraviolet, and X-rays — are also in the correct order.

So, everything in row iii seems to be correct. Row iii could definitely be the correct answer to this question. But just to double check, let’s also think about the final two rows.

Row iv suggests that X-rays and 𝛾 rays have the two longest wavelengths. We know this isn’t true; these waves actually have the two shortest wavelengths. So, row iv is not the correct answer.

Row v correctly lists the order of radio waves, microwaves, and infrared. However, visible light and ultraviolet are in the wrong order. Visible light has a longer wavelength than ultraviolet. So, row v can be ruled out.

This leaves us with row iii. Row iii is the only row that lists five types of electromagnetic wave in the correct order, from longest wavelength to shortest. So, the row of the table that correctly compares the wavelengths of various electromagnetic waves is row iii.

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