Finding value of unknown charge

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.
 

FAQ: Finding value of unknown charge

```html

How can I determine the value of an unknown charge using Coulomb's Law?

You can determine the value of an unknown charge using Coulomb's Law by measuring the force between two charges and knowing the distance between them. Coulomb's Law is given by F = k * |q1 * q2| / r^2, where F is the force, k is Coulomb's constant (8.99 x 10^9 N m^2/C^2), q1 and q2 are the magnitudes of the charges, and r is the distance between them. Rearrange the equation to solve for the unknown charge.

What equipment do I need to measure an unknown charge?

To measure an unknown charge, you will need a few key pieces of equipment: an electroscope or electrometer to measure electric charge, a known reference charge, a ruler or measuring tape to measure the distance between charges, and a device to measure the force between the charges, such as a force sensor or balance.

Can I use the principle of superposition to find an unknown charge?

Yes, the principle of superposition can be used to find an unknown charge. This principle states that the total force on a charge is the vector sum of the forces exerted by other individual charges. By setting up a system with multiple known charges and measuring the resulting forces, you can use vector addition to determine the unknown charge.

How does the method of induced charge help in finding an unknown charge?

The method of induced charge involves bringing a known charge close to a conductor and measuring the induced charge on the conductor. This can help in determining the unknown charge by analyzing the distribution of charges and using the principle of conservation of charge. The amount of induced charge can provide information about the magnitude of the unknown charge.

What role does Gauss's Law play in finding an unknown charge?

Gauss's Law can be used to find an unknown charge by relating the electric flux through a closed surface to the charge enclosed within that surface. According to Gauss's Law, the total electric flux through a closed surface is equal to the enclosed charge divided by the permittivity of free space (ε0). By measuring the electric field and knowing the geometry of the closed surface, you can calculate the unknown charge.

```

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