What am i doing wrong or right

  • Thread starter ziplock2k
  • Start date
  • #1
ziplock2k
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Homework Statement



A point charge of +2.7 mC is located at the origin of a coordinate system and a second point charge of -7.8 mC is at x = 1.5 m. At what point on the x-axis is the electrical potential zero? Calculate to 2 decimal places.

Homework Equations





The Attempt at a Solution



net pot. diff will be zero at
x=1/3.
and at x = -1.

pot. diff is a scalar qty. so u can directly add it.

if the net potential diff at a pt (say at x,0) is zero,
we have
(k*3/x) - (k*6/(1-x)) = 0
2x=1-x
x=1/3

Similarly for negative x, u can make n eqn:
-(k*3/x) - (-k*6/(1+x)) = 0
which shal give u: x=-1

WHAT AM I DOING WRONG?
 

Answers and Replies

  • #2
alphysicist
Homework Helper
2,238
2
Hi ziplock2k,

Homework Statement



A point charge of +2.7 mC is located at the origin of a coordinate system and a second point charge of -7.8 mC is at x = 1.5 m. At what point on the x-axis is the electrical potential zero? Calculate to 2 decimal places.

Homework Equations





The Attempt at a Solution



net pot. diff will be zero at
x=1/3.
and at x = -1.

pot. diff is a scalar qty. so u can directly add it.

if the net potential diff at a pt (say at x,0) is zero,
we have
(k*3/x) - (k*6/(1-x)) = 0

I don't understand what you are doing here. In particular, what are the 3 and the 6 in the numerators? And why is the denominator of the second term 1-x?
 
  • #3
ziplock2k
4
0
I'm sort of lost, as you can tell, and I need help.
 
  • #4
alphysicist
Homework Helper
2,238
2
I'm sort of lost, as you can tell, and I need help.

You may have done a problem similar to this before when you studied electric fields. This one is done much the same way.

The first step is, what is the formula for the electric potential of a point charge? (What confused me about your post was that you seemed to have the right form, but I did not understand where the numbers came from.)

So what is that formula, and what do they variable represent?
 

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