Find the electric field of a point P at a distance r

[Fatima Hasan]

Homework Statement

Homework Equations

The Attempt at a Solution

Can anyone check my answer please ?

 

[mfb]

Why did you rename the points?

In (a), you are asked about two points only, but calculating it for the third might help to see what went wrong.
Where did the prefactors come from (2,4,6)? It is difficult to find the error if you don't explain how you got these answers.

 

[Fatima Hasan]

Why did you rename the points?

In (a), you are asked about two points only, but calculating it for the third might help to see what went wrong.
Where did the prefactors come from (2,4,6)? It is difficult to find the error if you don't explain how you got these answers.

 

[mfb]

Why do you add and subtract the charge of the conducting shell?

There is no charge at the point of P2 or P3.

 

[Fatima Hasan]

Why do you add and subtract the charge of the conducting shell?

There is no charge in the conducting shell , so it's zero (+Q-Q=0)

 

[mfb]

The problem statement says the shells carry a charge -Q each.

 

[Fatima Hasan]

The problem statement says the shells carry a charge -Q each.

 

[mfb]

That is correct.

 

[haruspex]

View attachment 223540

Almost. You have a mistake in P₂ at the final step.

 

[Fatima Hasan]

Almost. You have a mistake in P₂ at the final step.

It should be $\frac{kQ}{(r_2)^2}$

 

[haruspex]

It should be $\frac{kQ}{(r_2)^2}$

Right.
What about part b? Do you wish to reconsider that answer?

 

[Fatima Hasan]

Right.
What about part b? Do you wish to reconsider that answer?

At P1 : $E=0$ , because $Q_{enclosed}=0$
At P2 : $E = \frac{-KQ}{(r_2)^2}$
At P3 : $E = \frac{-2KQ}{(r_3)^2}$

 

[haruspex]

At P1 : $E=0$ , because $Q_{enclosed}=0$
At P2 : $E = \frac{-KQ}{(r_2)^2}$
At P3 : $E = \frac{-2KQ}{(r_3)^2}$

Yes.

 

[mfb]

Almost. You have a mistake in P₂ at the final step.

Good catch, missed the sign.