Finding value of unknown charge

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The discussion centers on the direction of the electric field produced by an unknown charge, q, at the origin. It clarifies that if q is positive, the electric field points to the left, while if q is negative, the field points to the right, as a positive test charge would be attracted to the negative charge. The assumption that the electric field is always to the left is incorrect; the direction depends on the sign of q. The participants emphasize understanding the relationship between charge polarity and electric field direction. This highlights the importance of analyzing charge characteristics in physics problems.
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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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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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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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