How Can I Determine the Value of Charges in Coulomb's Law?

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    Coulomb's law Law
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SUMMARY

This discussion focuses on determining the value of charges using Coulomb's Law, specifically the formula F = k_E * q1 * q2 / r^2. The user seeks guidance on how to find the charge values (q1 and q2) without them being provided. It is established that measuring the force between two charges and their separation distance allows for the calculation of the product of the charges. If the charges are equal, knowing one charge enables the calculation of the other. Practical experimentation methods, such as using suspended charged objects, are also discussed.

PREREQUISITES
  • Understanding of Coulomb's Law and its formula (F = k_E * q1 * q2 / r^2).
  • Basic knowledge of Newton's laws of motion, particularly Newton's second law (F_net = a * m).
  • Familiarity with measuring force using a Newton meter.
  • Concept of measuring angles and forces in experimental setups.
NEXT STEPS
  • Research methods for measuring electric force between charged objects.
  • Learn about experimental setups for measuring charge values, including the use of suspended charged objects.
  • Study the implications of charge interactions in dynamic systems, including acceleration effects.
  • Explore the materials best suited for creating charged objects in experiments.
USEFUL FOR

This discussion is beneficial for physics students, educators, and hobbyists interested in experimental physics and the practical applications of Coulomb's Law in determining electric charge values.

Josh225
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Hello, I am pretty new to physics. I have no formal education on physics, and I have been studying it on my own out of curiosity and fascination. Please correct me if anything that I say is wrong and assume I know nothing. Math is also not my strongest skill, but I am trying to become better.

For the past couple of days, I have been working with Coulomb's Law. From my understanding the formula used is : (k) q1q2/r^2. I feel pretty comfortable with the formula and I have been doing some practice problems and getting them correct. In all of the questions though, q1 and q2 are given to me. I would like to know how to find the value of "q" without it being given to me.

If I were to construct my own experiment and put 2 charges at a certain distance from each other, how would I go about finding the value of the charges?

Thanks!
 
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##F=\frac{k_E \cdot q_1 \cdot q_2}{r^2}⇔q_1=\frac{F\cdot r^2}{k_E\cdot q_2}##
 
Thanks! What is that called so I can look more into it?
 
Josh225 said:
Thanki! What is that called so I can look more into it?
I do not think this equation ##q_1=\frac{F\cdot r^2}{k_E\cdot q_2}## has any name. Just another form of Coulomb law.
 
Josh225 said:
If I were to construct my own experiment and put 2 charges at a certain distance from each other, how would I go about finding the value of the charges?

From Coulomb's Law, if you measure the separation of the charges, r, and the force on either one, you could only find the product of the two charges, q1q2. If you knew the value of one of the charges then you could use the above formula to find the other. Also, if the two charges were equal, q1 = q2 = q, then Coulomb's Law would give you q^2 so you could calculate q.
 
How do I measure the force of the individual charge though?
 
Josh225 said:
How do I measure the force of the individual charge though?
##F_{coulomb}=F_{net}-F_{other}##
you can measure net force with Newton meter.
Or consider that Newton II law ##F_{net}=a*m## and measure acceleration and mass.
 
olgerm said:
Or consider that Newton II law ##F_{net}=a*m## and measure acceleration and mass.

This would get complicated if there is acceleration, i.e. the charges are not at rest, since then the separation distance, r, would be changing and the force would not be constant.

One possible experiment would be to suspend two charged objects on strings. The Coulomb force would cause the objects to attract or repel, depending on the charges, and the strings would deviate from the vertical. Knowing the mass of the objects and measuring the angle of deviation from the vertical, the Coulomb force can be calculated.
 
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As far are the 2 charged objects are concerned, what material would be the best to use? My knowledge on the subject is extremely limited.
 
  • #10
http://www.compadre.org/psrc/franklin/
Ben Franklin as my Lab Partner (Robert Morse)


http://mysite.du.edu/~jcalvert/phys/elechome.htm
http://mysite.du.edu/~jcalvert/phys/elechome.htm#Coul
 

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