# Electric field strength

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Thread starter 6 years ago
#1
A thin, isolated, spherical, conducting shell of radius a carries a charge +Q. Which one of the following graphs, A-E, illustrates how the electric field strength E varies with distance r from the centre of the sphere.

^ there is a selection of graphs very similar to the ones on that link.

So basically I thought it would be like the gravitational field graph:

http://notes.tyrocity.com/5-how-does...-of-g-explain/

And I chose the one that look like this (C) however the answer is actually the one that looks like (E). Could someone please explain why they differ?

Thanks
0
6 years ago
#2
(Original post by Davelittle)
A thin, isolated, spherical, conducting shell of radius a carries a charge +Q. Which one of the following graphs, A-E, illustrates how the electric field strength E varies with distance r from the centre of the sphere.

^ there is a selection of graphs very similar to the ones on that link.

So basically I thought it would be like the gravitational field graph:

http://notes.tyrocity.com/5-how-does...-of-g-explain/

And I chose the one that look like this (C) however the answer is actually the one that looks like (E). Could someone please explain why they differ?

Thanks
Outside the sphere the graph looks the same as the gravitational field for a planet.
Inside the sphere it's different.
In the gravitational case there is still a field inside the sphere.
In the case of an electric field there is no field inside a conducting sphere. E always = zero everywhere inside.

The red graph here.
http://hyperphysics.phy-astr.gsu.edu...ic/potsph.html

This is something you need to learn.
0
Thread starter 6 years ago
#3
(Original post by Stonebridge)
Outside the sphere the graph looks the same as the gravitational field for a planet.
Inside the sphere it's different.
In the gravitational case there is still a field inside the sphere.
In the case of an electric field there is no field inside a conducting sphere. E always = zero everywhere inside.

The red graph here.
http://hyperphysics.phy-astr.gsu.edu...ic/potsph.html

This is something you need to learn.
Thanks for the info

I'm doing past papers from the 80's so i don't know if it's on my current syllabus (not in the book or anything) but it'll be useful to know!
0
Thread starter 6 years ago
#4
(Original post by Stonebridge)
Outside the sphere the graph looks the same as the gravitational field for a planet.
Inside the sphere it's different.
In the gravitational case there is still a field inside the sphere.
In the case of an electric field there is no field inside a conducting sphere. E always = zero everywhere inside.

The red graph here.
http://hyperphysics.phy-astr.gsu.edu...ic/potsph.html

This is something you need to learn.
Also that link mentions the potential inside the charged sphere is constant (V) but I didn't really get their explanation, can you elaborate please?
0
6 years ago
#5
(Original post by Davelittle)
Also that link mentions the potential inside the charged sphere is constant (V) but I didn't really get their explanation, can you elaborate please?

The electric field is equal to the potential gradient.
If the field is zero the gradient is zero.
This means the graph is horizontal inside the sphere.

If there was a pd inside a conducting sphere charge would flow. As there is no flow of charge in the steady state (it is evenly distributed around the surface) there can be no pd.
No pd means the pd is the same everywhere.
0
Thread starter 6 years ago
#6
(Original post by Stonebridge)
The electric field is equal to the potential gradient.
If the field is zero the gradient is zero.
This means the graph is horizontal inside the sphere.

If there was a pd inside a conducting sphere charge would flow. As there is no flow of charge in the steady state (it is evenly distributed around the surface) there can be no pd.
No pd means the pd is the same everywhere.
Thanks and PRSOM
0
6 years ago
#7
(Original post by Davelittle)
Thanks and PRSOM
I just wanted to ask, do you have a link for the 80's past papers that you could share?

Thanks!
0
Thread starter 6 years ago
#8
(Original post by Zenarthra)
I just wanted to ask, do you have a link for the 80's past papers that you could share?

Thanks!
Really sorry my teacher printed them off for me, it's a selection of unit 4 past paper questions :/
0
6 years ago
#9
(Original post by Davelittle)
Really sorry my teacher printed them off for me, it's a selection of unit 4 past paper questions :/
Yo bro, photograph them and upload them, dont be gay.
1
6 years ago
#10
(Original post by Zenarthra)
Yo bro, photograph them and upload them, dont be gay.
HAHA
0
6 years ago
#11
(Original post by user1-4)
HAHA
ROFL, init bro he should upload them.
Hes a cheeky 1.
0
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