[Music] I'm welcome back to three size lessons.com okay by the end of this video you should be able to describe how changes in atoms can take place when electromagnetic radiation is generated or absorbed you should then be able to describe the hazards of ultraviolet x-rays and gamma-rays and if you are high a teen student you should be able to explain how radio waves can be produced so in this video we're looking at what happens when electromagnetic waves are generated or absorbed I'm showing you here a picture of lithium being heated a flame as you can see the lithium atoms are giving out red light and in the words they're emitting electromagnetic waves so how are these ways being produced here's a first key fact when electromagnetic waves are generated all absorbed changes take place in atoms or in the nuclei of atoms so I'm showing you here an atom of lithium when we heat atoms we cause electrons to move from one energy level to a higher one like this when this electron returns to its original energy level it generates an electromagnetic wave in this case light and I'm showing that here so as you can see a change to the atom has generated an electromagnetic wave now another way an electromagnetic wave can be generated as a change to the nucleus and a good example are gamma rays gamma rays can be emitted from the nucleus of radioactive atoms once the gamma ray has been emitted the new place has got less energy than it had at the start now there are a couple more points about this firstly when electromagnetic waves were absorbed that can also cause changes to atoms for example just like before electrons can change energy levels secondly electromagnetic waves can be emitted and absorbed over a wide frequency range from radio waves to gamma rays okay we're going to look now at the hazards of electromagnetic radiation ultraviolet waves x-rays and gamma rays are potentially very hazardous to the human body ultraviolet waves increase the risk of skin cancer and cause the skin to age prematurely x-rays and gamma rays are ionizing radiation in other words they knock electrons off atoms when they're absorbed because of this x-rays and gamma rays can cause the mutation of genes and this increases the risk of cancer now the damage caused by radiation depends both on the type of radiation and on the docks the dose of radiation is measured in sieverts or millisieverts now I should point out that you're not expected to remember the unit of radiation dose in you exam but you might be showing data on different doses and us to interpret it okay if you're a higher tier student you need to be able to explain how radio waves can be produced so we're going to look at that now radio waves can be produced when electrons oscillate an electrical circuit and the word oscillate means move backwards and forwards I'm showing you that here now these radio waves can be absorbed for example by an electrical circuit in an aerial and when this happens they now cause electrons in the circuit to oscillate this can create an alternating current with the same frequency as the radio waves remember you'll find plenty of questions on this topic in my revision workbook and you can get that by clicking on the link above [Music]