18
*
Centre of a collection of positive point charges is defined much the same way
as the centre of mass: r
r
cm =
∑
∑
q
q
i i
i
i
i Rationalised 2023-24
26
Physics
 EXAMPLE 1 9
Solution  (a) Field at P due to charge +10 mC
= 
5
12
2
1
2
10
C
4 (8 854 10
C N
m
)
−
−
−
−
π
×
2
4
2
1
(15
0