Distance from +4μC to Zero Potential: 24mm

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SUMMARY

The discussion centers on calculating the distance from a +4 μC charge to a point where the resultant electric potential is zero, given a -16 μC charge located 120 mm away. The correct distance is determined to be 24 mm from the +4 μC charge. Participants clarify that the potential equation requires using the magnitudes of the charges, leading to the conclusion that the ratio of the charges directly influences the distance calculation. The confusion arises from misapplying the potential equation, specifically the need to sum the potentials to equal zero.

PREREQUISITES
  • Understanding of electric potential and charge interactions
  • Familiarity with the potential equation in electrostatics
  • Basic algebra skills for solving equations
  • Knowledge of charge magnitude and its significance in calculations
NEXT STEPS
  • Review the electric potential equation and its application in electrostatics
  • Study the concept of charge ratios and their impact on electric potential
  • Practice solving problems involving multiple charges and resultant potentials
  • Explore the principles of superposition in electric fields and potentials
USEFUL FOR

Students studying physics, particularly those focusing on electrostatics, as well as educators looking for examples of charge interactions and potential calculations.

mrcotton
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Homework Statement


photobucket4_zps0655b6ef.jpg

The diagram shows two charges, +4 μC and –16 μC, 120 mm apart. What is the distance from
the +4 μC charge to the point between the two charges where the resultant electric potential is
zero?
A 24mm
B 40mm
C 80mm
D 96mm

Homework Equations



potential equation

The Attempt at a Solution



photobucket3_zps880c633e.jpg

Homework Statement



The correct answer is a 24mm
I get that we could simply use a 1:4 ratio and therefore r must be a fifth of the way from the 4 micro coulomb charge
However when I try and equate the formula and solve algebraicaly I seem to get the wrong answer if I put in the sign of the charges.

So my question is why do we just use the magnitude of the charges?
 
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mrcotton said:
So my question is why do we just use the magnitude of the charges?
You seem to have written U1 = U2 when you should have used U1 + U2 = 0.
 


Thank you, I am a fool
I must take a break and do some maths in between my physics
 

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