Physics 38 Electrical Potential (6 of 22) Electrical Potential Energy

[@dbmoney84]

Dear Prof: Just want to say thanks for making all these videos. I have a chronic illness and had to take time off from school, you definitely made coming back to school so much easier. How you break stuff down makes it seem a lot less daunting than it actually is. You've made a huge difference in my life.

[@MichelvanBiezen]

David, Glad to hear it. I admire you for despite having your challenges, you devote yourself to learning. Keep up the great work!

[@MichelvanBiezen]

Joe, Here is a good analogy, When you are lifting an object from the floor onto a table you are doing work against gravity. (That is positive work) When you take the object from the top of the table and lower it to the floor you are doing negative work.

[@kent.nguyen5314]

Hello Professor, if the book is lifted up, shouldn't that be negative work since the displacement and force vectors are opposite?

[@sheharyarali8057]

Ken T. Nguyen I think no because we are not taking in consideration the weight.. but our focus is on the force applied by hand lifting the book up.. force applied by the hand would be in the upwards direction that is the same direction of the displacement of the book hence positive work.

[@petereziagor4604]

This video helped me in my test last semester. Thanks a lot for the good work you're doing here.

[@MichelvanBiezen]

Glad it helped!

[@matrixate]

Thank you for the great lectures. You are truly gifted in explaining clearly.

[@orchoose]

''My old schooling failed me'' nice one:D also thanks for all the great lessons

[@bonnieandersona.brandao2677]

Thanks for all those classes! You are such a precious teacher!!! Thanks for this generosity

[@denis33333333333]

hey,your tutorials are really very good,it's easy to understand about what you're talking about.Thanks a lot.

[@juvydude]

I love you Mr. Biezen. your work is astounding and you really make a difference in many peoples' lives, including my own

[@MichelvanBiezen]

Thank you for sharing.

[@nomusanhlapo7051]

You're super awesome. Much love from South Africa

[@MichelvanBiezen]

Thank you for your comment. Welcome to the channel!

[@koheio.1222]

Thank you, thinking of it as separate steps of work helps

[@MyThundermuffin]

Mike...firstly words can't express how thankful I am to you. Whenever i am in doubt about a topic I immediately type michelvanbiezen ( in that same order lol ) on youtube, Not only for physics but for calculus and chemistry videos. I really appreciate that you take time from your schedule to educate us here over the internet and your videos are by far the best because you take what seems to be a difficult problem and simplify it so effortlessly.One day i hope i can meet you in person. Once again... thank you Mike

[@MichelvanBiezen]

MyThundermuffin, Thank you for your kind words. It is because of responses like yours that let me know that I am helping students around the world and it gives me great satisfaction to know that I am making a positive difference in the world, even if it is in a small way.

[@kidamaroo]

Since it matters where you put the charges (as he said), I think the question is a bit vague. It would be a much better question if they specified in the problem where exactly the charges were on the square.

[@arshadd672]

I love you. You are saving my grade right now.

[@HispanicMajority]

You are phenomenal!

[@MichelvanBiezen]

Lili, Thank you for the comment, that is very kind (although a little over the top). I just love science and I love to share my understanding with the world. You Tube has given me that opportunity and i am having a blast doing so.

[@Emk315]

Prof. Thank you so much for these video. I appreciate it.

[@MichelvanBiezen]

We are glad they are helpful.

[@xepho8205]

Thank you. I was never quite sure about how to round decimals to the appropriate number of sig figs in electromagnetism problems. Here you seem to have chosen to keep three significant figures. Is that because of the work done on charge 3, which contains a zero after the decimal, and the first significant figure would then be the second digit after the decimal?

[@MichelvanBiezen]

Significant figures are only important when actual measurements are taken in real life situations. Here we are just learning the theory and the techniques of solving these types of problems, so we are not concentrating on significant figures. (we are using made up numbers that are not measured)

[@MichelvanBiezen]

But technically speaking, if these were measured values, then the answer should be rounded to 1 significant figure ( 0.02)

[@xepho8205]

@@MichelvanBiezen Thank you very much:

[@meritnoah4013]

Nice lecture I love your lecture

[@MichelvanBiezen]

Thank you. Glad you find these helpful.

[@myzz9928]

Great lecture!

[@jfeel1262]

Excuse me sir, isn't the formula for work done is W=-qV ? But why don't you put the negative sign?

[@MichelvanBiezen]

Rather than memorizing a formula it is better to understand the formula and know why there is a positive or negative sign. When the work done ADDS energy to the system then you are doing positive work. If the work done reduces the energy of the system you are doing negative work. Bringing a positive charge closer to another positive charge requires positive work. Bringing a positive charge closer to a negative charge requires negative energy.

[@jfeel1262]

@@MichelvanBiezen ouhh..I understand now. Thank you so much prof😊

[@aishwaryaapandarinathan6067]

Hi I am from india.I understood it perfectly.

[@MichelvanBiezen]

Welcome to the channel.

[@kimwimisum511]

Thank you for all of your videos, Sir! I hope I'll get a good mark in our exam this Saturday. :)

[@김상우-l7e]

Hello sir, I really appreciate the explanation as to how you would approach in solving these types of problems. I just have some questions to ask - 1. How would you find the electric potential energy at the center of the system? (Like finding the electric potential energy at the center of the three charges you have given in the example.) 2. What is the connection between Electric Potential Energy and Electric Potential? Would a negative value in Electrical Potential Energy indicate a negative value in electric potential? How would you tie the two big concepts?

[@rabotkx2792]

does placing the charges in different positions change the value of the resulting work done?

[@MichelvanBiezen]

It depends on the symmetry. If the charges are exchanged, but the changed charges are at the same distancem ,then no. Otherwise moving the charges will change the final result.

[@MichelvanBiezen]

Not if they are at the same distance of one another. But typically, yes, the work done will be different.

[@theophile4real]

love all teachings. Thanks so much

[@omarosama4597]

thank you man for what you are doing keep up this work you are helping a lot

[@MichelvanBiezen]

Glad to help

[@hundle98]

so when a positive charge and a negative charge are an infinite distance away, they have infinite potential energy? Im assuming this because you are saying that potential energy decreases as you bring a positive charge and negative charge closer to each other.

[@MichelvanBiezen]

A good way to figure that out is to take two positive charges and place them infinitely far apart and call that the zero potential energy position. Now how much work would it take to bring them close together? The answer: PE = k * Q1 * Q2 / R It then would take the same amount of work to take a positive and negative charge (of the same magnitude) and pull them apart to infinity.

[@crystalsandoval2331]

Mr. van Biezen I tried this problem again placing the charges at different corners and am getting multiple different answers. How do I know where to place them to get the correct answer??

[@MichelvanBiezen]

Placing the charges in a different ORDER will result in a different answer. That is OK.

[@crystalsandoval2331]

So answers will vary for this problem?

[@MichelvanBiezen]

Depending on which order the charges (+ and -) are placed in.

[@crystalsandoval2331]

Thank you! You're the best!

[@smartteluguguru]

sir, I have doubt three charges must be placed in order of 4uC,-6uC,8uC,0uC but you placed in the order of 4uc,-6uC,0uC,8uC Is your charge representation correct?

[@MichelvanBiezen]

If you place them in a different order you will get a different answer. (That is not important as there were no specific instructions as to where to place them). How to do the problem is the important aspect.

[@iMAANfinity]

dear sir : if the question ask for potential difference and we get the value of V is negative since the formula is V=-Ed,should we include the negative or not if potential difference?

[@Academicallystressedout]

Why are using KQ/R instead of Kq/r^2

[@MichelvanBiezen]

V = kQ/R E = kQ/R^2

[@raspberry765]

Can one calculate the voltage at a place of interest and simply multiply it by the charge of interest that we have at that place to get the total potential energy?

[@MichelvanBiezen]

No, because that doesn't account for the work it took to place the initial charges there.

[@tudientan11]

you are my savior

[@ironuranium3927]

sir what is the meaning of negative and positive work ? Have any example in real life ?

[@MichelvanBiezen]

Lifting a book from the floor onto a table is doing positive work. Taking a book from the top of the table and placing it back on the floor is doing negative work.

[@hiraali7525]

so if i brought a chrge from infinty to the center of the square ? how would it effect the radius?

[@MichelvanBiezen]

That is a good question. You have to assume that the other charges remain where they are. (That is always assumed without mentioning it).

[@mrnarason]

So if all the charges were placed in the system at the same time, you would the same thing with W3 to W1 and W2 and add up the potential energies?

[@MichelvanBiezen]

+Victor P. yes

[@arnurmakenov4350]

Dear, Can we solve the problem using electric field?

[@MichelvanBiezen]

The method shown in the video is the best method.

[@imradkhan5755]

What does the negative work means? Tq very much..

[@frknklcsln]

Firstly thanks for these lectures they are very helpful.I wanted to ask if we placed the protons in a different order would it change the work done ?

[@MichelvanBiezen]

If the final configuration is different then probably yes. Otherwise no.

[@童乙]

Does "E&M" mean the problem is extremely hard?

[@MichelvanBiezen]

Not necessarily. E&M stands for electricity and magnetism

[@童乙]

Michel van Biezen Oh okay. I misunderstood it

[@nandhineekannan3990]

I'm from India ur are the best sir

[@MichelvanBiezen]

Welcome to the channel!

[@mostafaasmer5923]

Thank you so much professor for everything .❤ I mean it but there was a minor issue with this question as is i did it in 3 variations all in which plugging the Q in different corners and i get different answers so please notify me if iam incorrect

[@MichelvanBiezen]

Not sure what you mean by "different corners".

[@munyaradzizvakavapano5790]

the picture quality is poor

[@MichelvanBiezen]

Our videos are designed to be watched on a computer. We have added lighting on our newer videos.

[@Martin-zd9bv]

sir , i used the same method as yours but i got different answer if i placed the third charge below the second charge

[@MichelvanBiezen]

If you place the charges in a different arrangement you will get a different answer. (That is to be expected).

[@AngelAlita84]

great!

[@Baichannyyuri]

Hello professor its me again ~sorry for so many questions on difference videos of you, because I'm currently in physics 121 ~If i put an electron and its start to accelerated toward the proton the positive charge which is already theres in the first place, so the work done is negative because it moved to the lower potential energy. The final conclusion is higher potential energy moving toward the lower potential energy the work is negative PE(final)-PE(initial)=-W ? Can i bare thats in mind? opposite to that if lower potential energy moved to the higher potential energy ( the proton moving toward to another proton) would the Work be positive ? ...Oh my god sorry for the long question~ because its so confusing to mind visualize how everythings that work in the small scale in physics .

[@MichelvanBiezen]

If a negative charge moves closer to a positive charge (or a positive charge towards a negative charge) the potential energy decreases. There are some videos on that exact concept

[@olgucankeser9952]

good

[@riqyrizqyandra2206]

why W2 is negative?

[@MichelvanBiezen]

If it takes 10 J of work to lift an object from the floor to the top of the table, then it will take -10J of work (negative work) to "lift" the object from the top of the table to the floor. (Since the object loses potential energy, it required negative work). That is the same as W2. The second charge will lose potential energy by bringing it close to the first charge, since they attract. Thus it requires negative work to bring them closer.

[@ElifArslan-l9g]

thank you. you don't have to asnwer :)

[@MichelvanBiezen]

Thank you too!

[@lilibethcruz3284]

Isn't work supposed to be the negative of Vq so W=-Vq?

[@MichelvanBiezen]

That depends. When you bring 2 like charges closer together, you must do positive work because the potential energy of the system increases. When you bring 2 opposite charges close together, you must do negative work.

[@lilibethcruz3284]

You did mention it! Thanks, super helpful videos :)

[@AnCoSt1]

Words were eaten.

[@jaspersaffa4560]

Thank you 😊🚶🏽‍♂️

[@israeltomas6268]

why q2 is not affected by q3?

[@MichelvanBiezen]

q2 IS affected by q3. When you calculate the work done to bring charges together, you have to do it one charge at a time. When you place the first charge there, there are no other charges so it doesn't take any work. When you bring the second charge close to the first charge the third charge isn't there yet so you only calculate the energy between charge 1 and 2. But when you bring the third charge in, you must calculate the energy caused by q1 and q2 being close and the energy due to q2 and q3 being close.

[@yeasinpabel2436]

Michel van Biezen just awesome answer. Thanks from my heart.