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

Magnitude of Electric Field from an Atom

  • Thread starter Hypnos_16
  • Start date
153
1
1. Homework Statement

The neutral neptunium atom has 93 electrons.
What is the magnitude of its electric field at a distance of 6.5x10-10 m from the nucleus?

Hint: The number of protons in a nucleus is equal to the number of electrons in the neutral atom.

q = 1.6e-19 * 93 = 1.48e-17
r = 6.5e-10
k = 8.99e9

2. Homework Equations

E = kq / r2

3. The Attempt at a Solution

I would think that it would just be E = kq / r2 since we have all the variables we need.

E = kq / r2
E = (8.99e9)(1.48e-17) / (6.5e-10)2
E = 1.33e-7 / (6.5e-10)2
E = 3.16e11 => 3.16 x 1011 N/C

However turns out that isn't the right answer. So i took the hint into consideration, but can't see how it fits in to play. If there are 93 Electrons and 93 Protons wouldn't it mean the charge would just be 0?

Any help?
 
94
0
Can you apply Gauss's law at this radius?
 
153
1
Sure, but what will that do?

Gauss's Law = EA
= (3.16e11)(4π(6.5e-10)2)
= 1.67e-6
 

SammyS

Staff Emeritus
Science Advisor
Homework Helper
Gold Member
11,172
922
What is the size of such a atom?
 
94
0
Well, you can relate the charge enclosed within a surface to the electric field at the surface regardless of how the charge is distributed. So at the this radius what charge is enclosed?
 
153
1
Well, you can relate the charge enclosed within a surface to the electric field at the surface regardless of how the charge is distributed. So at the this radius what charge is enclosed?
-1.67e-6 = [k(q) / r2] * [4πr2]
-1.67e-6 / [4πr2] = [k(q) / r2]
-1.67e-6[r2] / [4πr2] = k(q)
-1.67e-6 / 4π = k(q)
-1.33e-7 = k(q)
q = -1.33e-7 / 8.99e9
q = -1.48e-17 N/C
 

Related Threads for: Magnitude of Electric Field from an Atom

Replies
2
Views
4K
  • Posted
Replies
3
Views
1K
Replies
9
Views
4K
  • Posted
Replies
4
Views
563
Replies
2
Views
4K
Replies
5
Views
6K
Replies
11
Views
12K

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