# Calculating Electric Field Strength between Charges

• jalen
In summary, the conversation discusses the calculation of the field strength between two charges of +4.0x10^-6 C and +8.0x10^-6C placed 2.0m apart, with a focus on determining the force at a point halfway between them. The correct answer is determined to be 3.6x10^4N/C toward the smaller charge, with the reasoning being that the forces of the two charges cancel each other out, resulting in a net force in the direction of q1.
jalen

## Homework Statement

q=4.0x10^-6C, 8.0x10^-6C
d=2m

## Homework Equations

Two charges of +4.0x10^-6 C and +8.0x10^-6C are placed 2.0m apart. What is the field strength halfway between them?

## The Attempt at a Solution

netEa= (9.0x10^9)(4.0x10^-6C) + (9.0x10^9)(8.0x10^-6C)
(2m)^2 (2m)^2

I assume by field strength, they want force, i.e. coulombs law.
Remember they want the strength at a point half way between them, half way being 1m from each of them. Use coulombs law for each charge with radius of 1m and then add the 2 forces together.

Chris

When you said with a radius of 1m you meant the (2m)^2 both become (1m)^2,right?

The answer in the text says 3.6x10^4N/C toward smaller charge but I got 1.08x10^5N/C if I used the(1m)^2 in my calculations...

netEa= (9.0x10^9)(4.0x10^-6C) + (9.0x10^9)(8.0x10^-6C)

(2m)^2 (2m)^2

Im not sure how you got that answer. 36000 is correct. Although I should correct myself by saying that you need to subtract the 2 forces because they are both positive, therefore oppose each other.

So, ((9x10^9)(4x10^-6))/1m^2 = 36000
((9x10^9)(8x10^-6))/1m^2 = 72000

The force of q2 is canceling out the force of q1. So 72000-36000 = 36000 in the direction of q1.
Make sense?

Chris

## 1. How do you calculate electric field strength between charges?

To calculate electric field strength between charges, you need to use the equation E = kQ/r^2, where E is the electric field strength, k is the Coulomb's constant (9x10^9 Nm^2/C^2), Q is the magnitude of the charge, and r is the distance between the charges.

## 2. What is the unit for electric field strength?

The unit for electric field strength is Newtons per Coulomb (N/C).

## 3. Can the electric field strength be negative?

Yes, the electric field strength can be negative. This indicates that the direction of the electric field is opposite to the direction of a positive test charge placed in the field.

## 4. What factors affect the electric field strength between charges?

The electric field strength between charges is affected by the magnitude of the charges, the distance between the charges, and the medium in which the charges are located.

## 5. How does the electric field strength change as the distance between charges increases?

As the distance between charges increases, the electric field strength decreases. This is because the electric field spreads out over a larger area, resulting in a weaker effect on a test charge placed at a certain distance from the charges.

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