What Was the Initial Charge on Sphere A in the Conducting Spheres Problem?

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SUMMARY

The discussion centers on determining the initial charge on sphere A in a problem involving four identical conducting spheres. Sphere W, initially uncharged, is sequentially touched to spheres A, B, and C, with known charges of 0, -29e, and +43e respectively. After these interactions, sphere W ends up with a final charge of +13e. The solution involves working forward from the known charges and applying the formula for charge distribution after contact, ultimately leading to the calculation of sphere A's initial charge.

PREREQUISITES
  • Understanding of electrostatics and charge distribution principles
  • Familiarity with the concept of conducting spheres and their behavior when touched
  • Knowledge of the formula Q = 0.5(q1 + q2) for charge sharing
  • Basic algebra skills for solving equations
NEXT STEPS
  • Study the principles of electrostatics, focusing on charge distribution in conductors
  • Learn about the behavior of conducting spheres when they come into contact
  • Practice problems involving charge sharing using the formula Q = 0.5(q1 + q2)
  • Explore advanced topics in electrostatics, such as capacitance and electric fields
USEFUL FOR

This discussion is beneficial for physics students, educators, and anyone interested in understanding electrostatic interactions and charge distribution in conducting materials.

a85liz
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Homework Statement


Figure 21-36 shows four identical conducting spheres that are actually well separated from one another.

Figure 21-36
Sphere W (with an initial charge of zero) is touched to sphere A and then they are separated. Next, sphere W is touched to sphere B (with an initial charge of -29e) and then they are separated. Finally, sphere W is touched to sphere C (with an initial charge of +43e), and then they are separated. The final charge on sphere W is +13e. What was the initial charge on sphere A?


Homework Equations



don't know

The Attempt at a Solution


I tried working backwards from the known charge and using the formula Q=.5(q1-q2). I am sure I am missing something simple, but I can not figure this problem out.
 
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a85liz said:

Homework Statement


Figure 21-36 shows four identical conducting spheres that are actually well separated from one another.

Sphere W (with an initial charge of zero) is touched to sphere A and then they are separated. Next, sphere W is touched to sphere B (with an initial charge of -29e) and then they are separated. Finally, sphere W is touched to sphere C (with an initial charge of +43e), and then they are separated. The final charge on sphere W is +13e. What was the initial charge on sphere A?

I tried working backwards from the known charge and using the formula Q=.5(q1-q2). I am sure I am missing something simple, but I can not figure this problem out.

Welcome to PF.

Maybe try working forwards? After touching A you know W carries 1/2A.

You know what B carries, so after touching B you have 1/2(1/2A + (-29))

So develop the formula for after touching C and knowing the final value, solve for A.
 

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