• Support PF! Buy your school textbooks, materials and every day products via PF Here!

Cant seem to get the answer right (E&M HW)

  • Thread starter cronxeh
  • Start date

cronxeh

Gold Member
949
10
The charge per unit length on a long, straight filament is -95.0 µC/m.

(a) Find the electric field 10.0 cm from the filament. Distances are measured perpendicular to the length of the filament. (Take radially inward toward the filament as the positive direction.)
My answer: 1.07 MN/C

(b) Find the electric field 29.0 cm from the filament.
My answer: 3.11 MN/C

(c) Find the electric field 120 cm from the filament.
My answer: 12.9 MN/C


Formula: 4*pi*8.99*10^9*distance*(-95*10^-6)

On the side of caution I've used both + and - aforementioned answers and both seem wrong. Am I missing something here?
I thought http://physics.villanova.edu/faculty/shaw/2402/extprob/m1224.gif [Broken] ?
 
Last edited by a moderator:

cronxeh

Gold Member
949
10
Also one more problem

A conducting spherical shell of inner radius of a and outer radius b carries a net charge Q. A point charge q is placed at the center of this shell.

(a) Determine the surface charge density on the inner surface of the shell. (Use Q, q, a, and b as necessary.)

My answer: -q/(4*pi*a^2)
(This is correct)

(b) Determine the surface charge density on the outer surface of the shell.
My answer: (Q+q)/(4*pi*r^2)
(This is marked wrong!)

Whats wrong about this answer? The WebAssign seems to think (Q+q)/(4*pi*r^2) and (Q+q)/(4*pi*a^2) for (b) are both wrong
 
13
0
i don't understand how you get your formula. i get
E=(-95*10^-6)/2*pi*R*ε0, as in formula in the image you gave link to.
 

OlderDan

Science Advisor
Homework Helper
3,021
1
cronxeh said:
A conducting spherical shell of inner radius of a and outer radius b carries a net charge Q. A point charge q is placed at the center of this shell.

(b) Determine the surface charge density on the outer surface of the shell.
My answer: (Q+q)/(4*pi*r^2)
(This is marked wrong!)

Whats wrong about this answer? The WebAssign seems to think (Q+q)/(4*pi*r^2) and (Q+q)/(4*pi*a^2) for (b) are both wrong
The radius of the outer surface is ?????.
 

Related Threads for: Cant seem to get the answer right (E&M HW)

Replies
2
Views
1K
Replies
1
Views
13K
Replies
1
Views
995
Replies
3
Views
9K
Replies
6
Views
2K
Replies
0
Views
718
Replies
2
Views
1K
  • Posted
Replies
2
Views
2K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top