- #1
Taylor_1989
- 402
- 14
Homework Statement
Hi guys, would just too make sure my derivation and insight to why is correct.
Question: a) only
Homework Equations
The Attempt at a Solution
$$dU=-wd_{ext}$$
$$dU=-F_{ext} \cdot dx$$
Now as the ##F_{ext}## is in the same direction and the direction vector { have not figured how to put direction vector in} then the equation becomes ##dU=-Fdx## this assume the direction is along the x-axis
So now if I intergrate both sides ##\int_{U(a)}^{U\infty}dU=-\int_{a}^{\infty}Fdx##
Subbing in a factoring columbs force law I get:
$$U(\infty)-U(a)=-kq_1q_2[-\frac{1}{x}]_a^\infty$$
Now U infity is zero because there is no force acting on it anymore and so I am left with##-U(a)## on the LHS on the RHS I am left with ##-kq_1q_2\frac{1}{a}##
thus the two negative cancel and I am left with the electric poteinal energy. Is this correct?