Electric Charge and Electric Fields

Electric Charge and Electric Fields

Professor Dave again, let’s discuss electric fields. We live in an age where we take electricity for granted. Just plug into the wall and you can power any device you want. But what’s in there? What is electricity made of? The discovery of a variety of phenomena over several centuries eventually led to our mastery of this incredible power, so let’s learn about it now. First we noticed that there was such a thing as electric charge. The easiest demonstration of this involves rubbing a balloon on your hair and seeing how the balloon will then attract your hair by some mysterious force. Two balloons that have been rubbed on your hair will strangely push each other away. This occurs because of electric charge, which is displaced by the rubbing together of these materials. The hair becomes positively charged and the balloons become negatively charged, which is terminology developed by Benjamin Franklin. Opposite charges will attract one another, which is why your hair sticks to the balloon, and like charges repel, which is why the two balloons push each other away. This property of electric charge is carried by certain subatomic particles. The most common of these are protons, which are positively charged, and electrons which are negatively charged. Along with neutrons these make up all the atoms in the universe. For more about atoms check out my general chemistry course. As it happens, electrons, which are the essence of electricity, are easily transferable and it is the transfer of electrons, in this case from your hair to the balloon, that generates electric charge in previously neutral materials. Each electron carries with it the fundamental charge, which is 1.6 x 10^-19 coulombs. This magnitude is negative for the electron and positive for the proton. All substances will therefore have a charge that is some multiple of this amount. That is to say, electric charge is quantized. We can categorize substances by their ability to transfer electric charge. A substance that can easily transfer electric charge is a conductor. One that can’t is an insulator. Opposite charges attract one another because of the electric force. This is outlined in Coulomb’s law, which states that the magnitude of the electric force between two objects is equal to the Coulomb’s constant times the charge on one object times the charge on the other divided by the square of the distance between them. Remarkably, this is essentially identical to Newton’s law of universal gravitation, the only differences being that the electric force can be attractive or repulsive depending on the signs of these terms and the resulting sign on the force, while gravity is always attractive. Also it is interesting to note that Coulomb’s constant is 20 orders of magnitude greater than the gravitational constant, illustrating the discrepancy in the strength of the two forces. This law also tells us that the electric force between two objects increases as charge increases and decreases as the distance between them increases. If more than two charges are present, vector addition must be done to find out the net force upon any particle in the system. Just as a gravitational field is what allows the gravitational force to propagate, it is an electric field that allows the electric force to propagate. However, as we said, the electric force is much stronger than gravity. This is evidenced by the fact that the repulsion between particles in your feet and particles in the ground is more than strong enough to keep you from plummeting towards the center of the earth. We can also use a cheap refrigerator magnet to keep a piece of paper on the fridge against the gravitational pull of the entire planet. Any charged object will manifest an electric field around itself, and if another charged object enters this field, interactions will occur. The strength of an electric field generated by a point charge is equal to the Coulomb constant times the charge on the object producing the field divided by the square of the distance between this object and whatever it is acting on. One way we depict electric fields is by drawing electric field lines, which generally point towards negative charges and away from positive charges, and do not cross. These don’t really exist, but they are a convenient way to analyze the direction of a field at any point in space, like the fields produced by these two oppositely charged particles, which we can call an electric dipole. The more densely packed the field lines are in a particular region, the greater the strength of the field. Lines like these can be especially useful if many particles are producing the field. How is it specifically that we use the electric force to our advantage? To find out, we have to move on to electric potential. But first, let’s check comprehension. Thanks for watching, guys. Subscribe to my channel for more tutorials, support me on patreon so I can keep making content, and as always feel free to email me:


    I love how you explain these concepts. I have no idea what i am looking at when i see the formulas, but i understand how and why things work the way they do. You have a very good approach that should be appealing to the average person. I certainly learned quite a few things . Keep up the good work and good luck.

    Question: Is the General Chem and Organic Chem all the videos you have for chemistry? Thank you..keep up the amazing work. Love your short and to the point videos!

    I am new subscriber n starting to watch n learn from your videos… I know this question isn't related to the topic of this videos. but I wud be nice if you give just a clear cut answer… what is the trend of shielding effect from left to right across the period… some books n webs n sources state it remains same across the period … n some wud say it decreases as the effective nuclear charge increases… it wud be nice if you give a clear cut answer… thanx

    first of all real thanx sir for replying… so the clearcut statement wud be that ""shielding effect remains same from left to right across the period""… hope I got it right..

    Professor Dave ,I am an Indian and an IIT (Indian Institute of Technology, aspirant.There are two competitive exams one have to write to get a seat in prestigious IIT colleges.I checked all the viedeos in your channel.All the videos​ are related to IIT portions.I am really gonna tell all my friends who are also IIT aspirants. Thanks a lot professor Dave.All the concepts are beautifully explained.Keep going your doing great.
    Thanks a lot professor.Have a nice day.☺

    Hi Professor Dave,
    Your explanation very outstanding.
    I want to ask one question that is;

    Sir it was a vey great video
    But i wanted to ask one question
    That why always electric field lines are directed outwards for positive charge and inwards for a negative charge?

    Word of warning: don't fly a kite with a wire in a thunderstorm and connect your phone to it, it'll be the wrong voltage and will damage your phone. Enjoy the video.

    hi prof . dave ,what is the similarity between electrostatic discharge and electric current.Are they the same phenomenon?

    For the checking comprehension exercise at the end, shouldn’t the force be negative because it’s between two protons and they’re both positively charged? Love the video by the way! It was helpful.

    I need electric field of 3 charges put in the vertices of an equilateral triangle please….HELP

    Great video. But I have a question. I get that you call something negatively charged when it has excess electrons because electrons are negatively charged. But what exactly makes electrons negatively charged or the protons positively charged?

    smart guy and good content.. didn't need the intro tho.. would just cut to the topic and minus the history.. unless this is for like idk elementary school kids

    Sir can you please explain why an insulator can freely give away its electron just by physical rubbing. Is it not related to ionisation energy? If so, should it not be difficult to displace electron from the stable covalently bonded species.

    Hey Professor Dave, I can't help but notice, what is that tattoo of because it looks pretty dope!
    Keep up the good work your getting me through grade 12 physics in the land down under, Australia!

    Prof, if two object get rubbed by friction on each other, how do we know the charge each object will carry (positive and negative) after transfer of charges.

    Sir what happens when a neutral body is placed in electromagnetic fields?does it experience any force?

    i don't understand how rubbing balloon to hair can transfer electrons, electrons move VERY slowly. Is it more like the "energy" we are transferring rather than electrons.

    You said q1q2/r2 which stands for radius but in comprehension, you measured diameter which was 5 meter. Which was the correct denominator

    by far your explanation is better, but you did not explain well what charge is, you explained how charge came about – i.e. by rubbing hair with balloon and what it can do….,,, and you explained type of charges – negatively and positively charged ……. and you explained how this charge behave or what it can do i.e. repel or attract,,,,, then you explained where we find this charge or who carry this charge i.e. proton carry positive charge electron carry negative charge. etc… … and slightly you mentioned charge is electron property ,,,,,,,,,,, but why not it is also proton property ?…….can we say charge is a kind of force? as it can push or repel? or attract and hold?

    Hello prof dave thx for your useful videos

    I have a question pls ansewer
    Maybe its bit stupid but really will help me

    Q/ if we have two negative charge has the same magnitude what happens
    They are stay static or will appear a force ??

    Hey Wait What , We have learnt in our textbooks that coloumb's law is only applicable for point charges not objects….. Is There any update in this discovery , Does this law works for objects also from now onwards ???? ….. Please Reply

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