Subjects
Maths
Chemistry
Biology
English Language
History
Responding to change (a2 only)
Infection and response
Homeostasis and response
Energy transfers (a2 only)
Cell biology
Organisms respond to changes in their internal and external environments (a-level only)
Biological molecules
Organisation
Substance exchange
Bioenergetics
Genetic information & variation
Inheritance, variation and evolution
Genetics & ecosystems (a2 only)
Ecology
Cells
Show all topics
Britain & the wider world: 1745 -1901
1l the quest for political stability: germany, 1871-1991
The cold war
Inter-war germany
Medieval period: 1066 -1509
2d religious conflict and the church in england, c1529-c1570
2o democracy and nazism: germany, 1918-1945
1f industrialisation and the people: britain, c1783-1885
1c the tudors: england, 1485-1603
2m wars and welfare: britain in transition, 1906-1957
World war two & the holocaust
2n revolution and dictatorship: russia, 1917-1953
2s the making of modern britain, 1951-2007
World war one
Britain: 1509 -1745
Show all topics
Physics
13 Dec 2025
37
5 pages
Savio Siby @avioiby_4nm7u9tda5z6
Ever wondered how your phone connects to WiFi, how X-rays see through your skin, or why microwaves heat... Show more
Electromagnetic waves are created when atoms or their nuclei change energy states. Think of gamma rays shooting out from radioactive atoms, or radio waves being generated by the electrical circuits in your phone when you stream music.
Radio waves work through oscillations in electrical circuits - basically electricity wiggling back and forth really fast. Your TV aerial picks up these waves and converts them back into electrical signals with the same frequency. It's like a wireless electrical connection!
Some EM waves are properly dangerous though. Ultraviolet waves, X-rays and gamma rays can seriously damage your body tissues. We measure this danger using radiation dose in sieverts (Sv) - basically how much risk you're exposed to.
UV rays are sneaky - they make your skin age faster and increase skin cancer risk. X-rays and gamma rays are even worse because they're ionising radiation. This means they can knock electrons off atoms, messing up your DNA and potentially causing cancer. That's why radiographers hide behind lead screens during X-rays!
Key Point The higher the radiation dose in sieverts, the greater the risk to your health - but don't panic, everyday exposure levels are incredibly low.
Radio waves power your Bluetooth headphones, TV broadcasts, and can even bounce off the atmosphere to reach places directly blocked by mountains. Microwaves don't just heat your dinner - they also carry WiFi signals and communicate with satellites because they pass straight through the atmosphere.
In microwave ovens, the waves make water molecules vibrate rapidly, heating your food from the inside out. Infrared radiation is basically heat energy - thermal cameras detect it to see in the dark, and all objects emit it (hotter things emit more).
Visible light travels through fibre optic cables as pulses, carrying your broadband internet at light speed. The light bounces along the cable's length like a game of ping-pong. X-rays can pass through soft tissue but not bone, making them perfect for seeing fractures.
All EM waves can be reflected, refracted, absorbed or transmitted depending on what they hit. Understanding these properties helps explain why your WiFi struggles through thick walls but radio waves travel for miles.
Remember Different EM waves interact with materials differently - that's why we use specific types for specific jobs.
The tiny slice of EM spectrum you can actually see gets split into different colours - each colour is just light with a different frequency. Filters work by absorbing certain wavelengths whilst letting others through, like sunglasses blocking UV.
An opaque object's colour depends on which wavelengths it reflects back to your eyes. A red apple absorbs all colours except red, which bounces back. White objects reflect everything, black objects absorb everything (which is why they get hot in sunlight).
All objects emit and absorb infrared radiation constantly. You're literally glowing with infrared right now! The hotter something gets, the more infrared it pumps out. Black surfaces are brilliant at both absorbing and emitting radiation compared to shiny or pale surfaces.
Here's the clever bit - any object at constant temperature absorbs and emits radiation at exactly the same rate. If it absorbed more than it emitted, it would heat up. Perfect black bodies would absorb absolutely everything that hits them, making them theoretical super-emitters too.
Cool Fact Earth acts like a black body, constantly balancing the solar radiation it absorbs with the infrared it emits back to space.
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.
You can download the app from Google Play Store and Apple App Store.
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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Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
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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
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 THE SCHOOLGPT. 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 THE SCHOOLGPT. 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
Savio Siby
@avioiby_4nm7u9tda5z6
Ever wondered how your phone connects to WiFi, how X-rays see through your skin, or why microwaves heat your food? It's all down to electromagnetic waves - invisible energy that travels through space at the speed of light. These waves... Show more
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Electromagnetic waves are created when atoms or their nuclei change energy states. Think of gamma rays shooting out from radioactive atoms, or radio waves being generated by the electrical circuits in your phone when you stream music.
Radio waves work through oscillations in electrical circuits - basically electricity wiggling back and forth really fast. Your TV aerial picks up these waves and converts them back into electrical signals with the same frequency. It's like a wireless electrical connection!
Some EM waves are properly dangerous though. Ultraviolet waves, X-rays and gamma rays can seriously damage your body tissues. We measure this danger using radiation dose in sieverts (Sv) - basically how much risk you're exposed to.
UV rays are sneaky - they make your skin age faster and increase skin cancer risk. X-rays and gamma rays are even worse because they're ionising radiation. This means they can knock electrons off atoms, messing up your DNA and potentially causing cancer. That's why radiographers hide behind lead screens during X-rays!
Key Point: The higher the radiation dose in sieverts, the greater the risk to your health - but don't panic, everyday exposure levels are incredibly low.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Radio waves power your Bluetooth headphones, TV broadcasts, and can even bounce off the atmosphere to reach places directly blocked by mountains. Microwaves don't just heat your dinner - they also carry WiFi signals and communicate with satellites because they pass straight through the atmosphere.
In microwave ovens, the waves make water molecules vibrate rapidly, heating your food from the inside out. Infrared radiation is basically heat energy - thermal cameras detect it to see in the dark, and all objects emit it (hotter things emit more).
Visible light travels through fibre optic cables as pulses, carrying your broadband internet at light speed. The light bounces along the cable's length like a game of ping-pong. X-rays can pass through soft tissue but not bone, making them perfect for seeing fractures.
All EM waves can be reflected, refracted, absorbed or transmitted depending on what they hit. Understanding these properties helps explain why your WiFi struggles through thick walls but radio waves travel for miles.
Remember: Different EM waves interact with materials differently - that's why we use specific types for specific jobs.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
The tiny slice of EM spectrum you can actually see gets split into different colours - each colour is just light with a different frequency. Filters work by absorbing certain wavelengths whilst letting others through, like sunglasses blocking UV.
An opaque object's colour depends on which wavelengths it reflects back to your eyes. A red apple absorbs all colours except red, which bounces back. White objects reflect everything, black objects absorb everything (which is why they get hot in sunlight).
All objects emit and absorb infrared radiation constantly. You're literally glowing with infrared right now! The hotter something gets, the more infrared it pumps out. Black surfaces are brilliant at both absorbing and emitting radiation compared to shiny or pale surfaces.
Here's the clever bit - any object at constant temperature absorbs and emits radiation at exactly the same rate. If it absorbed more than it emitted, it would heat up. Perfect black bodies would absorb absolutely everything that hits them, making them theoretical super-emitters too.
Cool Fact: Earth acts like a black body, constantly balancing the solar radiation it absorbs with the infrared it emits back to space.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
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.
You can download the app from Google Play Store and Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
0
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
App Store
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 THE SCHOOLGPT. 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 THE SCHOOLGPT. 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
Sociology