Hello, welcome to this lesson on non-ionizing electromagnetic radiation.

My name's Mr. Norris.

This lesson is from the unit called electromagnetic waves.

Now, non-ionizing electromagnetic radiation is incredibly important for so many things in the modern world: television signal, mobile phone signal, satellite TV, fibre optic broadband that's high speed to your home, Wi-Fi signal, 4G and 5G mobile signal when you're out and about.

It's all carried by non-ionizing electromagnetic radiation.

So it's a good idea to understand a little bit about how this works given that it's so important for the modern world and modern technology.

So let's get going.

The outcome of this lesson is hopefully, by the end of the lesson, you'll be able to explain the properties, uses and dangers of non-ionizing electromagnetic radiation.

Some keywords that will come up this lesson are frequency, non-ionizing, heating, oscillations and antenna.

You might like to go over the definitions of those keywords, which are shown on the screen now.

Each word will be explained as it comes up in the lesson.

This lesson is divided into three sections.

In the first section, we'll do a recap about ionising and non-ionizing frequencies of electromagnetic radiation.

In the second section, we'll focus on radio waves and microwaves.

And in the final section, we'll focus on infrared and Visible light.

Let's get going with the first section.

So a reminder that electromagnetic waves actually transfer their energy in tiny chunks or packets rather than continuously.

So the energy of electromagnetic radiation doesn't build up slowly.

It arrives kind of bit by bit in these tiny chunks.

And the energy transferred by one chunk or packet of electromagnetic radiation increases with the frequency of the radiation.

So what that means is the smallest amount of gamma ray, so one packet of gamma ray radiation, well, that's highest frequency.

So that is gonna transfer more energy than a single chunk of say, ultraviolet radiation, which has lower frequency.

So what this means is that only ultraviolet X-ray and gamma radiation have enough energy per packet of radiation that arrives to ionise atoms. And a reminder that ionising an atom means turning the atom into an ion.

So atoms are neutral, whereas ions have an overall charge.

So how electromagnetic radiation can ionise an atom is by forcing an electron to leave the atom, a bit like this.

The electromagnetic wave comes in and transfers energy to an electron, which then escapes the atom and then it's no longer an atom because it's lost a negatively charged particle.

So the positive and negatively charged particles no longer balance out and it's no longer an atom.

It's got an overall charge, so it's called an ion.

So ultraviolet X-ray and gamma radiation are called ionising electromagnetic radiation because they do that.

They can ionise atoms, for example, within living cells and that can cause harmful changes to how cells work.

We did talk about that in a lot more detail in the last lesson in this unit.

Exposure to ionising radiation can therefore, increase the risk of cancer because the ionising radiation can ionise atoms in living cells, causing harmful changes to how cells work, And that increases the risk of cancer.

However, this lesson is gonna focus on the non-ionizing kinds of electromagnetic radiation.

So the kinds of electromagnetic radiation which do not ionise atoms because the smallest amounts of those lower frequency kinds of radiation that can exist don't carry enough energy in a single packet to ionise an atom.

So that's radio waves, microwaves, infrared and visible light, which are non-ionizing electromagnetic radiation.

And I've just explained why that is.

A single packet of non-ionizing electromagnetic radiation, so those frequency ranges does not have enough energy to force electrons off atoms to form ions.

However, these frequencies of electromagnetic radiation do have enough energy to harm cells by heating, especially at high intensities.

And high intensity light in lasers can damage eyes, which is why the person in this picture is wearing eye protection when they're working with the lasers in the picture.

And that's not the only effect that non-ionizing kinds of electromagnetic radiation, radio waves, microwaves, infrared invisible light, that's not the only effect that they can have, heating effects.

They can also push electrical currents through electrical conductors in the right conditions and they Can trigger chemical reactions like photosynthesis.

Quick check on what we've just said.

Which types or frequencies of electromagnetic radiation are non-ionizing? Identify the ones which are non-ionizing.

Pause the video now.

Make sure you can do that.

Okay, let's see how you go on.

I'm sure you got this right.

It's the lowest frequency ones which are non-ionizing.

So radio waves, microwaves, infrared and visible light.

Ultraviolet, x-rays and gamma rays are ionising frequencies of electromagnetic radiation.

Well done if you got that right.

Time for a quick task on what we talked about so far in this lesson.

Part one, describe how the frequency of electromagnetic wave affects their ability to ionise atoms. Part two, explain why the ability of electromagnetic waves to ionise atoms changes with frequency.

And part three, state how infrared radiation can damage living cells.

Pause the video now and write a written answer to all three of those, please.

Off you go.

Well done for your effort with that task.

Let's see how you got on.

Here are some example answers.

Check that your answers include these ideas.

So firstly, how does the frequency of electromagnetic wave affect their ability to ionise atoms? Well, it's as simple as the higher the frequency, the more ionising electromagnetic waves are.

So light and electromagnetic waves with a lower frequency than light are non-ionizing, whereas ultraviolet X-rays and gamma ray frequencies are ionising because they're higher frequency.

Part two, explain why the ability of electromagnetic waves to ionise atoms changes with frequency.

Well, the answer is the higher the frequency, the more energy is transferred by a single packet of that radiation.

And that's just how energy is transferred by electromagnetic waves.

And part three, state how infrared radiation can damage living cells.

Infrared radiation can damage cells by heating them, causing burns.

Well done if you got that right and add anything to your answers that would improve them.

That takes us to the second section of the lesson.

We're gonna focus on radio waves and microwaves.

So the lowest frequency non-ionizing electromagnetic radiations.

So radio waves can transmit information for TV, radio, mobile phones, Bluetooth and Wi-Fi signals.

They really do a lot of work in the modern world.

And low intensity radio waves are passing through our bodies all the time.

Exposure to low intensity radio waves is not thought to be harmful though.

It's thought to be absolutely fine.

However, looking into an intense source of radio waves at close range could cause serious damage to the lens of your eye by heating.

So don't do that.

So how are radio waves produced? Well, to answer that question, we need to go back to some of the fundamentals about electromagnetic waves themselves because radio waves is just the lowest frequency electromagnetic wave.

So electromagnetic waves are oscillations or ripples that travel through invisible electric and magnetic fields, which are all around us.

So in the diagram on this slide right now, there's a representation of the electric field around a charged particle.

Charged particles have invisible electric fields around them.

So the charged particle is in the middle of that diagram.

It's the red circle with the plus on it for a positively charged particle.

And the white lines represent the invisible electric field lines, which would surround a charged particle.

And when a charged particle oscillates, so wobbles up and down or moves back and forth, then that is gonna cause surrounding electric and magnetic field lines, which are visible to oscillate as well, a bit like this in the animation.

So you can see ripples travelling outwards through the invisible electric field lines there.

And the electromagnetic waves created will have the same frequency of oscillation as the original charged particle's frequency of oscillation as it moved up and down.

And those electromagnetic waves with the same frequency as the particle's frequency of oscillation will then transfer energy into the surroundings as you saw in that animation.

So how radio waves are created by an aerial or an antenna is exactly the same principle really.

It's just that the charged particles, which are made to oscillate are electrons, flows of electric current up and down a metal aerial.

When electric current flows up and down or oscillates up and down a metal aerial, that's charged particles oscillating up and down a metal aerial, causing nearby electric field lines to also oscillate with the same frequency as the charged particles were oscillating up and down the aerial.

So have a look at this animation.

Just be really clear that there's one electron represented, which is gonna move up and down the aerial of that radio station.

And the horizontal line going across the middle of this diagram represents one electric field line, which, of course, would be invisible in reality.

So let's have a look at what happens when one electron in the antenna oscillates up and down.

So it's creating this radio wave oscillation.

When electrons in the antenna oscillate up and down the antenna, that creates the radio wave oscillation, which travels across space.

And of course, it can be picked up by receiving aerials.

More on that in a moment.

And we've said before, but it's worth saying again that the radio wave created will have the same frequency as the oscillations of current in the antenna.

By oscillations are current, of course, you might recognise that as when current flows one way, then the other way, then one way, then the other way, that's alternating current.

So you have to send alternating current up and down the aerial and that creates a radio wave in the surrounding space.

Oscillations of electric and magnetic fields in the surrounding space.

And, of course, radio waves are used to send information and we do that by varying the frequency or the amplitude of the radio wave.

It's worth showing this animation again just to focus this time on electrons in the receiving aerial, which are then caused to oscillate by an incoming radio wave.

And that's because so the radio waves, the incoming radio waves are being absorbed by the second antenna, the aerial, the receiver, and that is generating alternating current in that second aerial.

There's no alternating current until the wave arrives just then.

So when a radio wave is absorbed by a metal aerial, electrons in that receiving aerial are caused to oscillate and alternating current is created in that aerial.

So electrical charges are oscillating in that receiving antenna.

So the alternating current that is generated in that antenna has the same frequency as the radio wave that produced it.

And then that current is kind of interpreted by electronics, that varying current is, or alternating current is interpreted by electronics, which then converts that signal to produce useful information, like TV images or sound or information from the internet that was carried by those waves.

Time for a check on the key ideas of what we just said.

It should be a fairly simple check.

Match each type of antenna to how it works.

So we've got a radio wave transmitter and a radio wave receiver.

Which links to A and which links to B? Pause the video now and make sure you can do that.

Okay, hopefully you found this fairly straightforward.

In fact, they were already matched up 'cause in a radio wave transmitter, oscillating electric charges or alternating current causes electric and magnetic fields to oscillate.

And in a radio wave receiver, that's when the radio waves come in, oscillating electric and magnetic fields.

So the radio waves cause electric charges to oscillate in the radio wave receiver aerial.

So the radio wave is generating alternating current in the receiver.

In the transmitter, alternating current generates the radio wave and in the receiver, the radio wave generates alternating current with the same frequency.

Well done if you got that right.

So why are radio waves so useful for this kind of long-distance communication? Well, there's a couple of reasons.

The first one is that radio waves are transmitted very well through air.

They can also pass through the walls of buildings and through say tall trees and hedges, foliage, woods.

And also, radio waves can reflect off very large objects rather than being absorbed, which means they can potentially travel further.

Very low frequency radio waves bend, the proper word for that is defract, around large obstacles like hills and around the curve of the Earth.

And also, the very lowest frequency radio waves don't pass through a layer in the Earth's atmosphere called the ionosphere.

And that means they've got a very long range.

As we move to higher frequency radio waves, they actually reflect back down from the ionosphere, which means they potentially have a.

Their range is extended compared to what it otherwise would've been because of the reflection, it extends the range.

And even higher frequency radio waves and some microwaves actually pass through the atmosphere and transmit information to and from satellites.

So the very high frequency radio waves and microwaves pass through the ionosphere.

So they're the frequencies that have to be used to communicate with satellites.

And some microwave frequencies are also used for communication.

They travel in straight lines and often need what are called relay towers like this to pass microwave signals longer distances.

And actually, a satellite could be used instead of a relay tower.

So a microwave signal could be beamed to a satellite and the satellite could beam a signal back down to a different location on Earth to extend the range of a communication signal.

Moving on to microwave radiation.

That's pretty well absorbed by water and that's why moisture in the air, so lots of like heavy, dense clouds in storms, stormy weather, that can affect potentially very high frequency radio wave and microwave transmissions because those frequencies tend to be well absorbed by water molecules.

So that's a negative.

But this also has a very positive use in microwave ovens.

So microwave frequencies transfer energy to water molecules really efficiently.

And microwaves actually heat water by causing water molecules to spin.

So in that animation, I'm sure you'll have been looking at the representation of the invisible microwave, which causes the water molecules, which is two hydrogen atoms bonded to an oxygen atom.

That's why they have that shape in the animation.

You can see the microwave oscillation within a microwave causes those water molecules to spin.

So that means that food with a high water content, which is pretty much all foods really, can be heated by microwaves in a microwave oven.

So microwaves are actually absorbed by three to four centimetres of food.

So microwaves actually penetrate through the surface of food and by three or four centimetres into a chunk of food, all of the microwave energy which passes through the food has been absorbed.

That means microwaves actually cook food from the inside.

That's why food cooked in a microwave doesn't really get crispy on the outside because food in the microwave is being cooked from the inside because microwaves penetrate into food and cook food from the inside.

And microwave ovens have metal sides and a metal mesh in the glass door.

That's to reflect microwaves and stop them escaping.

Let's do a check on lots of the things we've just said about radio waves and microwaves.

Do each of the following use radio waves, microwave frequencies or both? Pause the video and answer that for each one of these four.

Okay, let's see how you got on.

Well, FM radio uses radio waves.

The clue is in the name there.

Satellite communication will use some frequencies of both.

You can use very high frequency radio waves.

You can also use microwaves to communicate with satellites.

Cooking food uses microwaves.

You can't really use radio wave frequencies for cooking food 'cause radio waves wouldn't really be absorbed by food.

You need to use microwaves, which are well absorbed by water molecules to cook food out of radio waves and microwaves anyway.

Mobile phone networks actually use some frequencies of both very high frequency radio waves and microwave radiation.

Well done if you got that right.

Okay, time for a task on what we've covered in this learning cycle on radio waves and microwaves.

There are five questions here that I'd like you to write written answers to.

So pause the video, read the questions carefully, and have a go at answering each question with your best effort.

Off you go.

Okay, well done for your effort on that task.

I'm gonna give you some feedback now.

So question one, describe how radio waves and microwaves could be produced using a metal antenna.

Your answer needs to be along these lines.

This is an example answer, so don't worry if yours isn't exactly like this, but you can improve yours based on this.

The answer is oscillations of electric charge, you might have said alternating current, in an antenna produce an electromagnetic wave of the same frequency.

Well done if your answer included those ideas.

Question two, describe what happens when a radio wave is received by an antenna.

You need to say something along the lines of the radio wave is absorbed by the antenna and the radio wave causes electric charges in the antenna to oscillate in the antenna with the same frequency.

You might have said the radio wave generates an electric current in the antenna with the same frequency or alternating current in the antenna with the same frequency.

Question three, explain why some radio frequencies are well suited for long-distance communication and broadcasting on Earth.

Your answer could have included lots of these ideas.

Radio waves are not absorbed by air, buildings or foliage.

Low radio frequencies bend around obstacles and the curve of the Earth, which extends their range.

And higher radio frequencies reflect back down from the ionosphere, also giving them a long range.

That's why they're suited for long-distance communication and long-distance broadcasting.

Question four, explain why microwave frequencies are suitable for satellite communications.

It's because they can pass through the atmosphere, a layer in the atmosphere called the ionosphere, you might have said.

And because they travel in straight lines, microwave signals can be aimed at individual satellites.

And then finally, question five, explain why microwave frequencies are suitable for cooking food.

It's because most foods have a high water content and microwave frequencies are absorbed well by water.

So transfer energy to water efficiently, heating it or transfer energy to food efficiently, heating it.

Well done if your answers included lots of those ideas.

You should pause the video now and make any improvements to your own work.

So this takes us to the final section of this lesson on non-ionizing electromagnetic radiation.

We've looked at radio wave and microwave frequencies in detail.

Now we'll look at infrared and visible frequencies in detail, which will complete all four frequency ranges of non-ionizing electromagnetic radiation.

So we've talked in this unit already about how all objects radiate electromagnetic waves all of the time and how all objects are mostly emitting infrared radiation at room temperatures.

And we've also mentioned about how thermal cameras measure the intensity of this infrared radiation from each part of an image and convert the intensity of infrared from each part of an image to a temperature.

And then that can be displayed as a colour in a thermal image, like on the picture on this slide.

Now, when objects get so hot that they glow, which happens at about 600 degrees C, then objects can start to emit both some visible light, as well as the infrared that they're emitting.

So they start by emitting infrared, which is lower frequency.

And then as objects get hotter, they emit more and more higher frequencies.

And eventually, at 600 degrees C, objects start to emit some visible light, which is higher frequency, as well as the lower frequency infrared that they were always emitting at the lower temperatures.

So what can infrared radiation do? Well, it can be absorbed by the surface of most objects heating up the object, but from the outside in.

So that's different to microwaves.

Microwaves could penetrate three or four centimetres into, for example, food to cook food from the inside.

Whereas infrared radiation cooks food from the outside.

Infrared radiation is absorbed by the surface of objects.

So this is used in heating elements.

So electrical wire with a high current that passes through them and they get so hot that they give out lots and lots of infrared and a bit of visible light as well.

But it's the infrared they're emitting, which is gonna do most of the heating.

So because they're so hot, they're emitting a little bit of visible light as well, which is why we can see them glowing.

So in the picture, we've got heating elements in an infrared heater, in a toaster and in a grill.

And of course, intense infrared radiation can cause burns because all electromagnetic waves can cause a heating effect.

It's just very pronounced with infrared radiation because infrared radiation is just the right frequency, just the right wavelength to be absorbed by almost all surfaces pretty well.

Let's do a check on what we've just said.

Which type or which frequency ranges of electromagnetic radiation is emitted by a hot heating element? Choose which answer you think is correct.

Okay, the correct answer is B.

A hot heating element still emits mainly infrared even though you can see it glowing, say orange, that's the little bit of light radiation.

It's the little bit of visible light radiation it's emitting, but it's still mainly giving out infrared.

That happens all the way up until objects reach a temperature of say, 6,000 degrees C.

Let's look at some more uses of infrared radiation now.

So because infrared radiation is invisible, it can be used in security systems because beams of infrared are invisible.

But a moving object will absorb and block that invisible infrared beam and that can set off an alarm.

So you can use that in burglar alarms and alarm systems and security systems. TV remote controls often use beams of infrared radiation to send information a short distance to a TV.

However, if there's something in the way of a remote control between the remote control and the TV, that might absorb the infrared radiation and the signal won't be able to get to the TV.

So you need a clear line of sight between a TV remote control and the TV.

What you can sometimes do is you can bounce the infrared signal off a wall though.

So if you point a TV remote control at a wall, that signal might reflect off the wall and still be picked up by the receiver in the TV.

Laptops, computers and video game controllers also sometimes use infrared to transmit data over short distances.

And again, you want a clear line of sight as possible to enable the data transmission by infrared.

Otherwise the infrared gets absorbed and the signal's blocked.

Infrared radiation is also often used to send information along optical fibres.

So we'll talk about that next.

So optical fibres, that just means fibre optic cables and there's pictures of them here.

What do they contain? They contain bundles of clear plastic fibres that can transmit either visible light or infrared signals along them.

And you can see in the right-hand image the light or infrared, in this case, it's red visible light that you can see travels within the fibres, reflecting from the inside surface of the fibres, all the way along until the light or the infrared signal comes out the other, like the very end of the fibre.

So it's a very efficient way of sending a signal at the speed of light because, of course, that is the speed that infrared and visible light travels.

So that means fibre optic cables can transmit huge amounts of information very quickly over long distances using a digital code, which basically just means flashes of light or flashes of infrared on or off, means creates a digital code of ones and zeros, ons and off signals.

Now, this can transmit more information more quickly than electric cables.

Electric cables contain copper wires within the plastic casing, whereas optical fibres contain these clear plastic fibres within the plastic casing, and the optical fibres are carrying flashes of visible light or flashes of infrared, whereas electric cables are carrying pulses of electricity or alternating current normally.

So fibre optic cables, I'm sure you'll have heard of fibre optic broadband, which is generally faster than your normal broadband, which would be carried by a phone line, which is an electric cable.

So fibre optic cables is a fantastic use of electromagnetic radiation, which has benefited people in society.

We can get faster internet basically.

And let's now talk about other uses of visible light frequencies of electromagnetic radiation.

So vision is an obvious one.

Our eyes can detect visible light and we see objects because of the light reflected off objects and into our eyes.

And cameras work in a similar way.

Cameras detect light using a light-sensitive computer chip, which is called a CCD.

In the past, light caused chemical changes on a special chemical film in the back of a camera.

So when light hits photographic film, it causes a chemical change on the film and changes colour.

That's how old-fashioned cameras work.

But most cameras now are digital and work by a light-sensitive computer chip detecting visible light.

LED bulbs emit mostly visible light that's different to older, less energy-efficient filament light bulbs, which got so hot that they glowed.

So they were emitting far more invisible infrared radiation than they were visible light, which is not very efficient for something which is supposed to be just lighting a room.

LED bulbs are much more efficient because they're mostly visible light, and barely any infrared at all.

Much more of their energy goes into lighting a room than heating it, making it much more efficient.

So let's do a check on some of the things we've just said about infrared radiation and visible light frequencies of electromagnetic wave.

Do each of the following applications use infrared, visible light or both? Make a decision for each one.

Pause the video now.

Off you go.

Right, let's see how you got on.

Photography uses visible light.

Thermal imaging uses infrared.

Fibre optic communication can use both.

It can use either flashes of visible light or pulses or flashes of infrared, invisible infrared, travelling down those bundles of clear plastic fibre optics.

Cooking food in a toaster uses infrared.

The toaster does glow orange, but that visible light isn't what cooks the bread and turns it into toast.

TV remote controls also use infrared radiation.

Well done if you got those right.

Okay, time to do a task now to summarise all of the key ideas in this lesson, I would like you to fill in this table to summarise the properties of each frequency range of non-ionizing electromagnetic radiation.

Some columns in the table can be merged as the properties are the same for all four frequency ranges of electromagnetic radiation.

There are some boxes in the table which you might need to make bigger in order to fit in as much information as might be useful to note down.

So pause the video, have a good go at filling in every box in this table to summarise the properties of non-ionizing electromagnetic radiation.

Off you go.

Right, well done for your effort on this task.

I'll give you some feedback now.

So what are they? Well, actually, all of these are the same, radio waves, microwaves, infrared visible lights are all the same thing.

They're electromagnetic waves with lower frequencies and longer wavelengths than ultraviolet.

From radio waves to visible light, frequency increases and wavelength decreases.

They all have the same speed in air and they're all non-ionizing.

What are their dangers? Well, actually, they are all the same.

At high intensities, they all cause heating.

Eyes are particularly vulnerable and high-intensity infrared radiation specifically can cause burns.

Here are some example uses of each frequency range, some example sources and some example absorbers of radio waves, microwaves, infrared, and visible light.

You should pause the video here and add any that you missed from your table.

Here's a summary of this lesson.

Radio waves, microwaves, infrared radiation and visible light are non-ionizing electromagnetic radiation, so they're not ionising, but they can harm cells by heating cells.

Radio waves are produced by oscillating current in an antenna or alternating current in an antenna.

When radio waves are absorbed, they cause or generate changing current, alternating current in the receiving antenna with the same frequency as the radio wave.

Radio waves and microwaves are used for long-distance communication, broadcasting and data transmission.

Microwaves are absorbed by water, so it can be used to cook food from within.

But infrared radiation cooks food from the outside in because infrared radiation is absorbed by the surface of objects.

Infrared radiation is used for heating and thermal imaging.

Visible lights and infrared radiation are used for data transmission in optical fibres.