# Field strength

• Feb 9th 2008, 03:58 PM
johett
Field strength
Two charges of +4.0x10^-6 C and +8.0x10^-6C are placed 2.0m apart. What is the field strength halfway between them?

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

This is what I have...which part is wrong?
• Feb 10th 2008, 12:25 AM
CaptainBlack
Quote:

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

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

This is what I have...which part is wrong?

They are 2m apart, so the point midway between them is 1m from each, and where are the $4 \pi \varepsilon_0$ terms?

RonL
• Feb 10th 2008, 02:04 PM
CaptainBlack
Quote:

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

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

This is what I have...which part is wrong?

and the two terms are in opposite directions so one of them should have a "-"