Electric potential when there is a negative test charge?

In summary, when a negative test charge is placed in an electric field, the work done to get from infinity to r would be negative, corresponding to a decrease in potential energy. Since dr must be a path element and therefore in the negative direction towards the source of the E field, the direction of the force experienced by the negative charge would be towards infinity. According to the definition of electric field and potential, the force experienced by a negative charge is always towards the direction of the source of the E-field, rather than the direction of the field's 'source'. This approach avoids the need for different rules for different combinations of charges and simplifies understanding.
  • #1
applestrudle
64
0
For when there is a negative test charge:

The work done to get from infinity to r would be negative, corresponding to a decrease in potential energy so

since dr must be a path element and therefore in the negative direction (towards the source of the E field)

does that mean the direction of the force I apply would be towards infinity?
 
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  • #2
I believe a negative charge experiences a force towards the direction of the source of the E-field.
 
  • #3
Drakkith said:
I believe a negative charge experiences a force towards the direction of the source of the E-field.

A field doesn't really have a 'source', though. A static E field exists between two charges or between a charge and infinity. It is far better just to start with the definition of field and potential (which involves energy or force associated with a Unit Positive charge) and just go along with where the signs of the charges and directions of any vectors etc. If you try to have a different rule for what will happen for every combination of charge sign, etc., then you are making life hard for you and your memory. Physics tries to avoid that sort of problem.
 

FAQ: Electric potential when there is a negative test charge?

1. What is electric potential?

Electric potential is a measure of the potential energy that a charged particle possesses in an electric field. It is also known as voltage and is measured in volts (V).

2. How is electric potential calculated?

Electric potential is calculated by dividing the work done by an external force to move a charged particle from one point to another in an electric field by the amount of charge of the particle. This can be represented by the equation V = W/q, where V is electric potential, W is work done, and q is charge.

3. What is a negative test charge?

A negative test charge is a hypothetical particle with a negative charge that is used to measure the electric potential at a point in an electric field. It is used to determine the direction and magnitude of the electric field.

4. How does a negative test charge affect electric potential?

A negative test charge affects electric potential by experiencing a force in the opposite direction of the electric field. The potential energy of the test charge decreases as it moves towards the source of the electric field.

5. Why is a negative test charge used instead of a positive test charge?

A negative test charge is used because it allows for easier and more consistent calculations of electric potential. This is because the direction of the electric field is always opposite to the direction of the force experienced by the negative test charge.

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