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Updated Mar 18, 2026
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Understanding Atomic Structure in Physics
Sara
@osaraii
1 / 4
Absorption and Emission of EM Radiation
Ever wondered why your black school jumper gets so hot in the sun whilst your white shirt stays cool? It's all about how electrons in atoms handle electromagnetic radiation. Electrons live in specific energy levels around the nucleus - think of them like steps on a ladder, with lower levels closer to the nucleus.
When electromagnetic radiation (like light or heat) hits an atom, electrons can absorb this energy and jump up to higher energy levels. Dark objects are brilliant at this, which is why they appear dark - they're not reflecting the light back to your eyes.
But electrons don't stay excited forever! They eventually drop back down to their original energy levels, and when they do, they emit electromagnetic radiation. This is actually how we get all the colours of light we see - it's just electrons moving between energy levels and giving off energy.
Key Point: All visible light comes from electrons moving down energy levels and emitting electromagnetic radiation - that's how your phone screen works!
Nuclear Equations and Half-Life
Alpha decay happens when an unstable nucleus spits out an alpha particle . The atomic number drops by 2 because the nucleus loses 2 protons. Beta decay is different - a neutron actually transforms into a proton and shoots out an electron at incredible speed.
Half-life is one of the most useful concepts you'll learn. It's the time it takes for half the radioactive nuclei in a sample to decay. If you start with 1000 radioactive atoms and the half-life is 10 minutes, you'll have 500 after 10 minutes, 250 after 20 minutes, and so on.
Irradiation means exposing something to radiation - like getting an X-ray. The object doesn't become radioactive itself. Contamination is much worse - that's when radioactive material actually gets onto or into something, making it radioactive too.
Exam Tip: Remember that background radiation is everywhere - from cosmic rays to granite rocks. It's completely normal and measured in Sieverts!
Nuclear Applications in Medicine and Energy
Nuclear medicine is genuinely amazing! Doctors use radioactive tracers like radioactive iodine to check your thyroid gland. These tracers must emit gamma radiation (so it can pass through your body), have a short half-life (so they don't hang around), and not be too ionising.
Radiotherapy uses ionising radiation to destroy cancer cells. It's incredibly precise, though some healthy tissue might get damaged too. The key is targeting the cancer whilst minimising harm to everything else.
Nuclear fission happens when massive, unstable nuclei (like uranium) split apart, releasing enormous amounts of energy. Nuclear fusion is the opposite - light nuclei (like hydrogen) join together to form heavier ones. Both processes convert some mass into energy, but fusion doesn't create a dangerous chain reaction like fission can.
Real-World Connection: The sun runs on nuclear fusion, turning hydrogen into helium and giving us all the energy that powers life on Earth!
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The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
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Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
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Best app on earth! no words because it’s too good
Thomas R
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Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Understanding Atomic Structure in Physics
Sara
@osaraii
Nuclear physics might sound intimidating, but it's actually all around us - from the light bulbs in your room to medical treatments saving lives. This topic covers how atoms absorb and emit energy, what makes some atoms radioactive, and how... Show more
Absorption and Emission of EM Radiation
Ever wondered why your black school jumper gets so hot in the sun whilst your white shirt stays cool? It's all about how electrons in atoms handle electromagnetic radiation. Electrons live in specific energy levels around the nucleus - think of them like steps on a ladder, with lower levels closer to the nucleus.
When electromagnetic radiation (like light or heat) hits an atom, electrons can absorb this energy and jump up to higher energy levels. Dark objects are brilliant at this, which is why they appear dark - they're not reflecting the light back to your eyes.
But electrons don't stay excited forever! They eventually drop back down to their original energy levels, and when they do, they emit electromagnetic radiation. This is actually how we get all the colours of light we see - it's just electrons moving between energy levels and giving off energy.
Key Point: All visible light comes from electrons moving down energy levels and emitting electromagnetic radiation - that's how your phone screen works!
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Nuclear Equations and Half-Life
Alpha decay happens when an unstable nucleus spits out an alpha particle . The atomic number drops by 2 because the nucleus loses 2 protons. Beta decay is different - a neutron actually transforms into a proton and shoots out an electron at incredible speed.
Half-life is one of the most useful concepts you'll learn. It's the time it takes for half the radioactive nuclei in a sample to decay. If you start with 1000 radioactive atoms and the half-life is 10 minutes, you'll have 500 after 10 minutes, 250 after 20 minutes, and so on.
Irradiation means exposing something to radiation - like getting an X-ray. The object doesn't become radioactive itself. Contamination is much worse - that's when radioactive material actually gets onto or into something, making it radioactive too.
Exam Tip: Remember that background radiation is everywhere - from cosmic rays to granite rocks. It's completely normal and measured in Sieverts!
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
Nuclear Applications in Medicine and Energy
Nuclear medicine is genuinely amazing! Doctors use radioactive tracers like radioactive iodine to check your thyroid gland. These tracers must emit gamma radiation (so it can pass through your body), have a short half-life (so they don't hang around), and not be too ionising.
Radiotherapy uses ionising radiation to destroy cancer cells. It's incredibly precise, though some healthy tissue might get damaged too. The key is targeting the cancer whilst minimising harm to everything else.
Nuclear fission happens when massive, unstable nuclei (like uranium) split apart, releasing enormous amounts of energy. Nuclear fusion is the opposite - light nuclei (like hydrogen) join together to form heavier ones. Both processes convert some mass into energy, but fusion doesn't create a dangerous chain reaction like fission can.
Real-World Connection: The sun runs on nuclear fusion, turning hydrogen into helium and giving us all the energy that powers life on Earth!
Sign up to see the contentIt's free!
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We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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4.7/5
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user