Finding electric field between two charges

[joel amos]

Homework Statement

Two charges, Q₁ = 4*10^-8 and Q₂ = 2.7*10^-8 are 3.25 m apart.
What is the electric field magnitude halfway between them?

Homework Equations

E = kQ/r²

The Attempt at a Solution

E₁= k (4*10^-8C)/(1.63m)²
= 135 N/C
E₂= k (2.7*10^-8C)/(1.63m)²
= 91.4 N/C

135 N/C - 91.4 N/C = 43.5 N/C

Is this correct?

 

[TSny]

Yes. You will get somewhat different answers depending on how you round your numbers during the calculation.

 

[haruspex]

Looks ok. Do you have a reason to doubt it?

 

[Simon Bridge]

It is best you don't rely on someone else to tell you if you are right or not.
Take this opportunity to practice :)

There are only two ways you are likely to be wrong in this problem:
1. you got the numbers wrong
2. you got the physics wrong

for 1 you just check your substitution
for 2 you go through your reasoning to see if your answer is consistent with the way charges behave.
When you start out doing this stuff it seems quite hard but you'll quickly get used to it.