Finding value of unknown charge

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    Charge Value
In summary: This is in contrast to the electric field due to a positive charge which would be pointing to the left as a positive test charge would be repelled by the positive charge.
  • #1
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Homework Statement
Please see below
Relevant Equations
Please see below
For this problem,
1674021666843.png

The solution is,
1674021637296.png

However, why did they assume that the electric field produced by charge q is always pointing to the left at the origin?

Many thanks!
 
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  • #2
Callumnc1 said:
Homework Statement:: Please see below
Relevant Equations:: Please see below

For this problem,
View attachment 320613
The solution is,
View attachment 320612
However, why did they assume that the electric field produced by charge q is always pointing to the left at the origin?

Many thanks!
They are not assuming that the electric field is pointing to the left.

Think about it.

If ##q## is a positive charge, then indeed, the electric field at the origin, due to ##q##, is to the left (negative).

What if ##q## is negative? Then you have a negative number multiplied by a negative number. In what direction is the electric field, due to ##q##, pointing in this case?
 
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  • #3
SammyS said:
They are not assuming that the electric field is pointing to the left.

Think about it.

If ##q## is a positive charge, then indeed, the electric field at the origin, due to ##q##, is to the left (negative).

What if ##q## is negative? Then you have a negative number multiplied by a negative number. In what direction is the electric field, due to ##q##, pointing in this case?
Thank you for your reply @SammyS !

If ##q## is negative, then the electric field due to the charge will be pointing to the right as a positive test charge would be attracted to the negative charge.
 

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