A2 Physics Electric Fields

Field lines show the force on a positive point charge


Posted from TSR Mobile

I still don't get it. + and - attract each other. The + exerts an electric force on - and the - exerts and electric equal and opposite force on + (N3L, right?). So don't both have a force on each other that gets them together, meaning + goes to - and - goes to +. I feel so confused.

Yeah they do but the definition of an electric field line is that it shows the direction of the force on the imaginary positive point charge they arwnt intended to shiw the eqaual and opposite force... therefore as the picture shows lines go into the positive charge and lines go 'out' of the negative... If u have 2 point charges negative and positive the field lines join up as shown as they show the force that a positive point will experience it will be repelled from the positive and attracted to the negative therefore the arrows go from the positive to the negative shown


Posted from TSR Mobile

So by convention, an electric field line shows the electric force from + towards -.

If we have + point charge, then the electric field lines go AWAY from it. If we

It's kind of like the arrow's tail, by convention, represents a + charge and the head represents a - charge, right?

Yeah but it's better not to think of it like that... All field lines do is show the direction of the force a positive point charge will experience if it was put at that position... so say it was put exactly between the two it would obviously speed off towards the negative charge which the field lines show...

Hope this helps it would be much easier to explain in person


Posted from TSR Mobile

"a line of force/electric field line is DEFINED as the path a POSITIVE test charge would follow." (how i remember)

hence, when near a POSITIVE POINT CHARGE (the big charge), the TEST CHARGE (little charge) will be REPELLED, meaning the field lines point AWAY from the point charge.

when near a NEGATIVE POINT CHARGE, the TEST CHARGE will be ATTRACTED towards it, meaning the field lines are directed TOWARDS the point charge.


I hope this is a easier way of helping you understand :-)

Thank you very much
+rep

thankyou!

Can you help me in this question please?


I need the charge of a proton right? But it doesn't even say it and it's not even on the formulae sheet for Edexcel.

Thanks a lot

Can you help me in this question please?


I need the charge of a proton right? But it doesn't even say it and it's not even on the formulae sheet for Edexcel.

Thanks a lot

Do you have the answer by any chance?
i've tried working it out on a peice of paper for you :-) so i'll post it after this :-)

Yes, it is 8.2 X 10^-8 N.

Your working out? I think I know how to do it though, my problem is I don't know the proton charge.

Thanks

ooooooh sorry! totally mis-read what you was saying... so sorry about that!

yes the charge of a proton is the same as that of an electron but different signs so the charge of a proton is +1.6x10-19 :-)

So then why do we sometimes use +1.6 X 10^-19 for the electron charge?

I think you can use +1.6x10-19 for either proton or the electron if the direction of the electrostatic force isn't needed/isn't important.

The +ive and -ive signs in these sorts of questions are there to show the direction of the forces. (from what i can remember)

remember force is a vector so it has magnitude AND direction so if you get a question about the direction i think that it's likely to do with the +ive or -ive sign.

I was on AQA so you may not even need to know about this in your spec!

THANK YOU!

So I use + for proton charge and - for electron charge, right? Then wouldn't that make charge be a vector quantity?