Electromagnetic waves

Did you hear about them before?

Do you know what they are?

As you can see below, electromagnetic waves are made up with two fields, one is electric and the another is magnetic. Both fields are perpendicular each other. The energy of the wave is stored in those domains. They don't need a material medium to propagate.

This is the electromagnetic radiation spectrum

You can notice that it is continuous, namely, there are no interruptions.

There are a lot of them, here you can see their effects, benefits, and damages

By means of this peak, we can identify the intensity of absorption, after that, we will find the correlate value in the Newton’s disc.

Newton’s disc

If the Newton’s disc is spun quickly, we shall see white

In the prior example; we had seen that the object absorbs in the 450 nm range. When it happens the object will reflect the sum of the other colours, and we shall see the opposite colour, that is, if the object absorbs in the 450 nm range (it’s equivalent to the blue), so we will see the opposite, namely orange.

When we use a prism it can separate light into the colors of the spectrum. Here we get the opposite effect of Newton’s disc rotation.

The microwave oven can be used to cooking and warming meals. There is a interesting question here, how does it work?

The basic principle is microwaves interact with water molecules , absorb energy and transfer those to the meal and warm it.

If you read the microwave oven instruction manual, you will see that you mustn’t cover meals with metallic foils, the most commonly used in cooking are aluminium foils. Because they make a barrier to preventing the microwaves from heating the meal. It works like a Faraday’s cage.

Here, we can see Wendy talking with her daughter Amanda, they are using mobile phones, their voices are transmitted by radio waves.

Hi mum, what’s up?

Hi Amanda! I’d like to

know if I can pick you up,

right now, are you ready?

Yeah, I’m waiting for you,

bye

At this moment, we can make an experiment in the classroom. We need two mobile devices. Firstly we make a call to check that the mobile phones are working. Secondly we wrap one of them with a piece of aluminium foil. In your opinion, what do you reckon will happen?

After this very exciting lesson, I would like to ask you a favour, switch your mobile off, please.