Solving Magnitude of Charge Problem with Coulomb's Law

In summary: The electric field is uniform along the length PQ.The electron is released from point P and passes point Q at time t = 1.00 × 10−2 seconds. The magnitude of both charges is unknown, but they must have the same magnitude in order for the electric field to be uniform.
  • #1
bidhati
9
0

Homework Statement



Two charges Q1 and Q2 of equal magnitude but opposite signs are fixed a distance 5.00 m apart in a vacuum The line PQ is a 12.0 cm section of the line joining the two charges and is placed centrally between them. Over the distance PQ the electric field may be taken to be uniform. An electron is released, with negligible initial speed, from point P at time t = 0. At t = 1.00 × 10−2 s the electron is observed to pass point Q. Determine the magnitude and sign of both Q1 and Q2

Homework Equations



Fel = 1/ 4 pi E q1q2 / r^2
a = 2s / t^2


The Attempt at a Solution


well basically I think I need another equation to combine with coulomb's law so I can make Q the subject and thus find the magnitude of charge.

I know that Fel is inversely proportional to r^2 and that if I find Q I just need to halve the value as both charges are equal.
as for the last part of the question electron = - so Q2 = + and thus Q1 = -


obviously there is something I am missing here a helpful pointer please?
 
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  • #2
I think u need find the change in electrostatic P.E as it moves from P to Qwhich will give an equation in q. Equate this to the kinetic energy gained. Hope this helps.
 
  • #3
Well, the electric field changes with time... as the charges are of opposite signs, they will accelerate towards each other and hence the magnitude of the field will change... You need to find the change in the field and then calculate the variable force on the electron.
 
  • #4
chaoseverlasting said:
Well, the electric field changes with time... as the charges are of opposite signs, they will accelerate towards each other and hence the magnitude of the field will change... You need to find the change in the field and then calculate the variable force on the electron.
The electric field is uniform along the length PQ.
 
  • #5
bidhati said:

Homework Statement



Two charges Q1 and Q2 of equal magnitude but opposite signs are fixed a distance 5.00 m apart in a vacuum The line PQ is a 12.0 cm section of the line joining the two charges and is placed centrally between them. Over the distance PQ the electric field may be taken to be uniform. An electron is released, with negligible initial speed, from point P at time t = 0. At t = 1.00 × 10−2 s the electron is observed to pass point Q. Determine the magnitude and sign of both Q1 and Q2

Since the charges are opposite, the +ve carge Q1(lets say) will be towards Q and the negative charge will be towards P. Now calculate the total force acting on the electron , repulsion due to Q2 and attraction due to Q1. Thus you'll get the acceleration of the electron. This will help solve for the unknowns
 

FAQ: Solving Magnitude of Charge Problem with Coulomb's Law

1. How do I determine the magnitude of charge using Coulomb's Law?

To determine the magnitude of charge using Coulomb's Law, you will need to know the values of the two charges involved, the distance between them, and the value of the Coulomb's constant. You can then use the formula Q = (k * Q1 * Q2) / r^2, where Q is the magnitude of charge, k is the Coulomb's constant, Q1 and Q2 are the charges, and r is the distance between them.

2. Can Coulomb's Law be used for both positive and negative charges?

Yes, Coulomb's Law can be used for both positive and negative charges. The only difference is that the force between two like charges (either both positive or both negative) will be repulsive, while the force between two unlike charges (one positive and one negative) will be attractive.

3. What is the Coulomb's constant?

The Coulomb's constant, denoted by k, is a proportionality constant that relates the magnitude of electric force between two charged particles to the distance between them and the magnitude of their charges. Its value is approximately 8.99 x 10^9 N*m^2/C^2.

4. What are the units for the Coulomb's constant?

The units for the Coulomb's constant, k, are N*m^2/C^2. This can be derived from the units of force (N), distance (m), and charge (C) in the equation F = (k * Q1 * Q2) / r^2.

5. Can Coulomb's Law be used for objects with non-point charges?

Yes, Coulomb's Law can still be used for objects with non-point charges. However, in this case, the distance between the charges should be measured from the center of each object, and the charges should be treated as if they are concentrated at their respective centers of mass.

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