17.4 CHAPTER 17. ELECTROSTATICS
U =
kQ 1 Q 2
r=(8. 99 × 109 )(7× 10 −^9 )(20× 10 −^9 )
(0,02)
= 6, 29 × 10 −5J
Electrical potential ESBHL
The electrical potentialat a point is the electrical potential energy per unit charge, i.e. the potential
energy a positive test charge would have if it were placed at that point.
Consider a positive testcharge +Q placed at A in the electric field of another positive point charge.
+ ��
+Q
A B
The test charge moves towards B under the influence of the electric fieldof the other charge. In the
process the test charge loses electrical potentialenergy and gains kineticenergy. Thus, at A, the test
charge has more potential energy than at B – A is said to have a higher electrical potential than B.
The potential energy ofa charge at a point in a field is defined as the work required to move that
charge from infinity to that point.
DEFINITION: Potential difference
The potential difference between two points in an electric field is defined as the work
required to move a unitpositive test charge fromthe point of lower potential to that
of higher potential.If an amount of work W is required to move a charge Q from one point to another, then the potential
difference between thetwo points is given by,