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Updated Apr 15, 2026
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Understanding Electric Forces and Fields
1 / 9
The Basic Principle of Electric Force
Think of electric charges like invisible magnets attached to every bit of matter around you. Objects with electric charge naturally push or pull on each other without even touching - it's a proper non-contact force that's constantly at work.
Here's the golden rule you need to memorise: like charges repel, opposite charges attract. Two positive charges will shove each other away, two negative charges do the same thing, but a positive and negative charge will pull towards each other like best mates.
This might seem simple, but this force literally holds atoms together and creates almost every force you experience daily (except gravity). Your pen staying on the table? That's electric forces between atoms doing their job.
Electric charge comes in two flavours - positive (+) and negative (-) - and we measure it in Coulombs (C). An electron carries -1.6 × 10⁻¹⁹ C whilst a proton carries +1.6 × 10⁻¹⁹ C, which is the smallest possible chunk of charge.
Quick Tip: Remember that electric force is a vector - it has both strength and direction, just like when you push a shopping trolley.
Understanding Electric Fields
Here's where it gets interesting - charges don't just magically reach across space to grab each other. Instead, every charged object creates an electric field around itself, like an invisible influence zone that fills the space nearby.
Think of it this way: charge Q sets up the field, and when you place another charge q in that field, it feels a force. The field is always there, waiting to act on any charge that wanders into it.
We use something called a test charge (a tiny positive charge) to map out these fields. It's like sending a scout to check what forces are lurking in different spots around a charged object.
Electric field lines help us visualise these invisible fields. They're imaginary lines that show exactly what would happen to a positive test charge - the direction of the line shows which way the force would push it.
Key Rule: Field lines always start on positive charges and end on negative charges, and they never cross each other (that would be chaos!).
Field Line Patterns
Picture field lines shooting outwards from a positive charge like spokes on a bicycle wheel - they point away because a positive test charge would be repelled and pushed outwards.
For a negative charge, it's the complete opposite. Field lines point inwards towards the charge because a positive test charge would be attracted and pulled in.
When you've got both positive and negative charges together, the field lines create beautiful curved paths that start on the positive charge and end on the negative one. It's like watching invisible highways that show exactly where the forces flow.
Visual Tip: The closer together the field lines are, the stronger the field - think of it like traffic density on a road.
Electric Field Strength Calculations
Now for the maths bit - electric field strength (E) tells us exactly how powerful the field is at any point. It's defined as the force per unit positive charge, which gives us the formula: E = F/q.
The units are Newtons per Coulomb (N C⁻¹), and you can rearrange this to find force: F = E × q. This is your go-to equation for exam questions.
Let's say you place a +4µC test charge in a field and it experiences 0.02 N of force to the left. Your field strength is 0.02 ÷ (4 × 10⁻⁶) = 5000 N C⁻¹ to the left.
Here's the tricky bit that catches loads of students: if you put an electron (negative charge) in an upward-pointing field, the force on it points downward - opposite to the field direction.
Exam Warning: Always remember that field direction is defined by what happens to a positive charge. Negative charges experience force in the opposite direction!
Worked Example - Force on an Electron
Let's tackle a classic exam question. An electron sits in a uniform electric field of 200 N C⁻¹ pointing upwards. What's the force on the electron?
First, gather your info: E = 200 N C⁻¹ (upward), and electron charge = -1.6 × 10⁻¹⁹ C. Use F = E × q to get the magnitude: F = 200 × 1.6 × 10⁻¹⁹ = 3.2 × 10⁻¹⁷ N.
For direction, remember that the field points where a positive charge would be pushed. Since our electron is negative, it gets pushed the opposite way - downward.
Answer: 3.2 × 10⁻¹⁷ N downward. The key is separating magnitude (ignore the negative sign) from direction (use the negative sign to reverse the field direction).
Success Strategy: Always convert microcoulombs (µC) to coulombs (C) before calculating - multiply by 10⁻⁶.
Revision Essentials
You've got this! The core concept is beautifully simple: like charges repel, opposite charges attract. Everything else builds from this fundamental rule.
Electric fields exist around every charged object, and we use field lines to map them out. These lines start at positive charges, end at negative charges, never cross, and show field strength through their spacing.
For calculations, master E = F/q and its rearrangement F = E × q. Remember your units (N C⁻¹ for field strength) and always watch the direction - positive charges follow field lines, negative charges go against them.
The trickiest exam errors happen with directions and unit conversions, so double-check these every time. Once you've nailed the basics, you'll find that electric fields explain so much of the physics happening around you every day.
Final Tip: In uniform fields (like between parallel plates), field lines are parallel and equally spaced - same field strength everywhere!
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Elisha
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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
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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 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 Electric Forces and Fields
Ever wonder how your phone's touchscreen works or why your hair stands up when you rub a balloon on it? It's all about electric forces and fields- invisible forces that control everything from the atoms in your body to... Show more
The Basic Principle of Electric Force
Think of electric charges like invisible magnets attached to every bit of matter around you. Objects with electric charge naturally push or pull on each other without even touching - it's a proper non-contact force that's constantly at work.
Here's the golden rule you need to memorise: like charges repel, opposite charges attract. Two positive charges will shove each other away, two negative charges do the same thing, but a positive and negative charge will pull towards each other like best mates.
This might seem simple, but this force literally holds atoms together and creates almost every force you experience daily (except gravity). Your pen staying on the table? That's electric forces between atoms doing their job.
Electric charge comes in two flavours - positive (+) and negative (-) - and we measure it in Coulombs (C). An electron carries -1.6 × 10⁻¹⁹ C whilst a proton carries +1.6 × 10⁻¹⁹ C, which is the smallest possible chunk of charge.
Quick Tip: Remember that electric force is a vector - it has both strength and direction, just like when you push a shopping trolley.
Sign up to see the contentIt's free!
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Improve your grades
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Understanding Electric Fields
Here's where it gets interesting - charges don't just magically reach across space to grab each other. Instead, every charged object creates an electric field around itself, like an invisible influence zone that fills the space nearby.
Think of it this way: charge Q sets up the field, and when you place another charge q in that field, it feels a force. The field is always there, waiting to act on any charge that wanders into it.
We use something called a test charge (a tiny positive charge) to map out these fields. It's like sending a scout to check what forces are lurking in different spots around a charged object.
Electric field lines help us visualise these invisible fields. They're imaginary lines that show exactly what would happen to a positive test charge - the direction of the line shows which way the force would push it.
Key Rule: Field lines always start on positive charges and end on negative charges, and they never cross each other (that would be chaos!).
Sign up to see the contentIt's free!
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Field Line Patterns
Picture field lines shooting outwards from a positive charge like spokes on a bicycle wheel - they point away because a positive test charge would be repelled and pushed outwards.
For a negative charge, it's the complete opposite. Field lines point inwards towards the charge because a positive test charge would be attracted and pulled in.
When you've got both positive and negative charges together, the field lines create beautiful curved paths that start on the positive charge and end on the negative one. It's like watching invisible highways that show exactly where the forces flow.
Visual Tip: The closer together the field lines are, the stronger the field - think of it like traffic density on a road.
Sign up to see the contentIt's free!
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Electric Field Strength Calculations
Now for the maths bit - electric field strength (E) tells us exactly how powerful the field is at any point. It's defined as the force per unit positive charge, which gives us the formula: E = F/q.
The units are Newtons per Coulomb (N C⁻¹), and you can rearrange this to find force: F = E × q. This is your go-to equation for exam questions.
Let's say you place a +4µC test charge in a field and it experiences 0.02 N of force to the left. Your field strength is 0.02 ÷ (4 × 10⁻⁶) = 5000 N C⁻¹ to the left.
Here's the tricky bit that catches loads of students: if you put an electron (negative charge) in an upward-pointing field, the force on it points downward - opposite to the field direction.
Exam Warning: Always remember that field direction is defined by what happens to a positive charge. Negative charges experience force in the opposite direction!
Sign up to see the contentIt's free!
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Worked Example - Force on an Electron
Let's tackle a classic exam question. An electron sits in a uniform electric field of 200 N C⁻¹ pointing upwards. What's the force on the electron?
First, gather your info: E = 200 N C⁻¹ (upward), and electron charge = -1.6 × 10⁻¹⁹ C. Use F = E × q to get the magnitude: F = 200 × 1.6 × 10⁻¹⁹ = 3.2 × 10⁻¹⁷ N.
For direction, remember that the field points where a positive charge would be pushed. Since our electron is negative, it gets pushed the opposite way - downward.
Answer: 3.2 × 10⁻¹⁷ N downward. The key is separating magnitude (ignore the negative sign) from direction (use the negative sign to reverse the field direction).
Success Strategy: Always convert microcoulombs (µC) to coulombs (C) before calculating - multiply by 10⁻⁶.
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
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Revision Essentials
You've got this! The core concept is beautifully simple: like charges repel, opposite charges attract. Everything else builds from this fundamental rule.
Electric fields exist around every charged object, and we use field lines to map them out. These lines start at positive charges, end at negative charges, never cross, and show field strength through their spacing.
For calculations, master E = F/q and its rearrangement F = E × q. Remember your units (N C⁻¹ for field strength) and always watch the direction - positive charges follow field lines, negative charges go against them.
The trickiest exam errors happen with directions and unit conversions, so double-check these every time. Once you've nailed the basics, you'll find that electric fields explain so much of the physics happening around you every day.
Final Tip: In uniform fields (like between parallel plates), field lines are parallel and equally spaced - same field strength everywhere!
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
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?
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Is Knowunity really free of charge?
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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 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