Electric field problem -- Repulsive force between two charged spheres

AI Thread Summary
The discussion centers on the repulsive force between two charged spheres that touch and then separate, leading to a change in force. It is noted that the charges equalize upon contact, resulting in an average charge of 2.5 nC. The challenge lies in determining the original charges of the spheres before they touched. Additionally, the size of the spheres is important, as the problem assumes they are much smaller than 20 cm in radius to avoid complications in charge distribution. Understanding these factors is crucial for accurately solving the electric field problem.
Dezzi
Messages
2
Reaction score
0
Homework Statement
Two identical spheres have charges q1 and q2. When they are 20 cm apart, the replusive force between them is 1.35×10^‐4N. After they touched together and separated once again to 20cm, the replusive force between them is 1.406×10^-4N. FIND q1 and q2. (Ans 20nC; 30 nC)
Relevant Equations
F=kQ1Q2/r^2
I attempt to solve the problem in the picture below.
 

Attachments

  • Screenshot_20211031-145927_Drive.jpg
    Screenshot_20211031-145927_Drive.jpg
    14 KB · Views: 127
  • 16357071656697539725904243983068.jpg
    16357071656697539725904243983068.jpg
    25.8 KB · Views: 140
Physics news on Phys.org
Why is the force different the second time?
 
PeroK said:
Why is the force different the second time?
The question say " they touched together and separated once again"
 
Dezzi said:
The question say " they touched together and separated once again"
So, what changed?
 
PeroK said:
So, what changed?
I guess the charges get equalised. So, you've worked out that average charge: ##2.5 nC##, which looks right.

The hard bit is to figure out what the original charges were. Any ideas?
 
A quibble: since the spheres are evidently conductors, the question ought to specify that the spheres are much smaller than 20cm radius. Otherwise the charge distributions complicate matters.
 
Reply
  • Informative
  • Like
Likes PeroK and berkeman

Thread 'Errors and significant figures'

I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
View full post »
Thread 'A cylinder connected to a hanging mass'

Thread 'A cylinder connected to a hanging mass'

Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
View full post »

Similar threads

Induced charge on a conducting sphere sliced by a plane
Replies
2
Views
1K
Electric field external to Conducting Hollow Sphere with charge inside
Replies
23
Views
3K
Work done to insert a point charge 𝑞 at the center of a conducting sphere
Replies
12
Views
1K
The electric potential inside a conducting sphere with charge Q
Replies
11
Views
1K
Flux of Electric field through sphere
Replies
2
Views
2K
Induced polarization for collision between conducting spheres
Replies
4
Views
1K
Should I Consider the Electric Field Outside a Uniformly Charged Sphere?
Replies
2
Views
3K
Magnetization of a paramagnetic sphere
Replies
11
Views
1K
Electric Field Inside a Conducting Sphere: Is it Always Zero?
Replies
1
Views
1K
Use of imaginary charge vs Gauss' law
Replies
12
Views
894

Hot Threads

Recent Insights

Back
Top