Calculating Forces in Electrostatic Fields w/ q & 4q

AI Thread Summary
To calculate the forces acting on two fixed charges 'q' and '4q' separated by 5 cm, the electric field equation E = (k*q)/r² is used, leading to the force equation F = k*q*Q/r². The specific values of the charges are not provided, but the relationship between them is crucial, as the force will depend on the magnitude of 'q'. It is important to convert the distance from centimeters to meters for accurate calculations. The final answers should express the forces in terms of q², highlighting the different forces acting on each charge. Understanding these concepts is essential for solving electrostatic problems effectively.
bansal321
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Hello i have a problem that i need help with.

Two fixed charges 'q' and '4q' are positioned along an axis with a separation d=5cm

a) Calculate the forces acting on each charge

Attempt
- I understand that the the force eqn is F = qE
- I also understand that i need to work out the Electric field before i can calculate the force
- and the electric field eqn is E = (k*q)/r^2??

what i don't understand is what are the values for the charges? There is no specific value for them, but they are written as 'q' and '4q'

Can anyone please offer some clarity to this please.

Thank you
 
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You haven't been given the value of q but it certainly matters - the higher the q, the stronger the forces. So you will have a "q" in your answers.

You can use E = (k*q)/r^2 and then F = QE or put it together and just use
F = k*q*Q/r².
 
Thank you for the response!

ok so i understand now to use F = k*q*Q/r^2

for the charge 'q' i have => (9*10^9)*q*Q/25 => (3.6*10^8)*q*Q

would that be the final answer? Can i multiply q*Q to get Q^2? or should i just leave it as that?
 
Careful, you must convert your cm to meters. You don't want the two different Q's to appear in the final answer. Just put in "q" for one charge and "4q" for the other. You'll end up with a number times q².

The question actually asks for TWO forces, so you should really say something about the force on the q and the force on the 4q and how they are different.
 
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