Ranking the force of point charges problem

In summary, the problem involves 5 point charges, each with a specific charge and distance from a spherical shell with a uniform charge. Using Coulomb's law, we can calculate the force exerted on each charge by the shell. The charges can be ranked in order of increasing force, with q2 having the least force and q5 having the greatest force. The negative symbol does not affect the magnitude of the force, so it does not need to be considered when ranking the charges.
  • #1
macaco
14
0

Homework Statement



5 point charges;
q1; charge = +q distance = d
q2; charge = +2q distance = 3d
q3; charge = -3q distance = 2d
q4; charge = -4q distance = 3d
q5; charge = -5q distance = 2d
are placed in the vicinity of an insulating spherical shell with a charge (+Q), distributed uniformly over its surface.
Rank the point charges in order of the increasing magnitude of force exerted on them by the sphere. Indicate all ties where appropriate. Show all calculations of force.

Homework Equations



Coulomb's law;
F= K (q1)(q2)
---------​
r^2​

The Attempt at a Solution


I've applied coulomb's law to each of the charges, substituting each of the values in;


q1=> F= K Qq
-----​
d^2​

q2=> F= K 2Qq
------​
3d^2​

q3=> F= K -3Qq
------​
4d^2​

q4=> F= K -4Qq
------​
9d^2​

q5=> F= K -5Qq
-------​
4d^2​

I'm still not sure how to rank the equations after I've substituted the values?
I.e.- How do I tell which is higher when I have no numerical value for each?

should I be solving the equations somehow?

Any help much appreciated
 
Physics news on Phys.org
  • #2
Hi macaco! :smile:

(try using the X2 tag just above the Reply box :wink:)

This is really messy, and almost unreadable …

do everything as a factor of qQ/d2

and forget the signs (the + or -) … they're only asking for the magnitudes, so it doesn't matter. :wink:
 
  • #3
You're a legend Tiny Tim.
(The legend of Tiny Tim; sounds like a good book title =P)

Didn't think of taking out a common factor.

The charges in ascending order, according to the values left would be;
q2=> 0.66
q1=> 1
q4=> 1.33
q3=> 1.5
q5=> 2.5

(hopefully)

Thanks again TT

=]
 
  • #4
The one thing I did not understand, is why you would not use the negative symbols, and rank the negatives below the positives?
 
  • #5
Hi macaco! :smile:

(just got up :zzz: …)
macaco said:
The one thing I did not understand, is why you would not use the negative symbols, and rank the negatives below the positives?

Because the question specified …
macaco said:
Rank the point charges in order of the increasing magnitude of force …

and the definition of "magnitude" is that you're only interested in the size, not the direction …

so the magnitude of a negative number -x is x, the magnitude of a vector (such as force) is its length, and the magnitude of a complex number a + ib = re is √(a2 + b2) = r. :wink:
 
  • #6
thanks again TT
 

1. What is the purpose of ranking the force of point charges problem?

The purpose of ranking the force of point charges problem is to determine the relative strength of the electric force between multiple point charges. This can help in understanding the behavior of charged particles and predicting their movement in an electric field.

2. How do you rank the force of point charges?

To rank the force of point charges, you need to calculate the electric force between each pair of charges using Coulomb's law. Then, you can compare the magnitudes of these forces to determine which ones are stronger and which ones are weaker.

3. What factors affect the ranking of the force of point charges?

The ranking of the force of point charges can be affected by the magnitude of the charges, the distance between them, and the medium in which they are located. Additionally, the direction of the charges and the angle between them can also impact the ranking.

4. Can the force of point charges ever be negative?

Yes, the force of point charges can be negative. This occurs when the charges have opposite signs and are attracting each other. The negative sign indicates that the force is directed in the opposite direction of the positive charge.

5. How is the ranking of the force of point charges useful in real-world applications?

The ranking of the force of point charges is useful in various real-world applications, such as designing electronic circuits, studying the behavior of charged particles in particle accelerators, and analyzing the behavior of molecules and atoms in chemistry and biology.

Similar threads

  • Introductory Physics Homework Help
Replies
4
Views
752
  • Introductory Physics Homework Help
Replies
21
Views
605
  • Introductory Physics Homework Help
Replies
2
Views
1K
  • Introductory Physics Homework Help
Replies
8
Views
2K
  • Introductory Physics Homework Help
Replies
9
Views
1K
Replies
17
Views
878
  • Introductory Physics Homework Help
Replies
9
Views
3K
  • Introductory Physics Homework Help
Replies
5
Views
12K
  • Introductory Physics Homework Help
Replies
10
Views
5K
  • Introductory Physics Homework Help
Replies
16
Views
2K
Back
Top