# Electric field problem -- Repulsive force between two charged spheres

• Dezzi
In summary, the conversation discusses an attempt to solve a problem involving two spheres that touch and then separate, resulting in a different force each time. The question is raised about what causes the force to change and it is suggested that the charges get equalized. The main difficulty lies in determining the original charges of the spheres.
Dezzi
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.

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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.

PeroK and berkeman

## 1. What is an electric field?

An electric field is a region around a charged object where other charged objects experience a force. It is created by the presence of a charged object and can be either attractive or repulsive depending on the charge of the objects involved.

## 2. How does the repulsive force between two charged spheres relate to the electric field?

The repulsive force between two charged spheres is a result of the electric field created by the charges on the spheres. The electric field exerts a force on the charges, causing them to repel each other.

## 3. What factors affect the strength of the repulsive force between two charged spheres?

The strength of the repulsive force between two charged spheres is affected by the magnitude of the charges on the spheres, the distance between the spheres, and the medium in which the spheres are located. The force increases with the magnitude of the charges and decreases with the distance between the spheres. The medium can also affect the force through its dielectric constant.

## 4. How is the repulsive force between two charged spheres calculated?

The repulsive force between two charged spheres can be calculated using Coulomb's law, which states that the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between the spheres. The formula is F = (k * q1 * q2) / r2, where k is the Coulomb's constant, q1 and q2 are the charges on the spheres, and r is the distance between them.

## 5. Can the repulsive force between two charged spheres be completely eliminated?

Yes, the repulsive force between two charged spheres can be completely eliminated if the charges on the spheres are equal in magnitude and opposite in sign. In this case, the electric field between the spheres will be zero, and there will be no force of repulsion. This is known as a neutralization reaction.

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