Question

What is the strength of the electric field 2.4 cm from a small plastic bead that has been charged to -9.0 nc ?

Answer 1

We can assimilate the small bead as a single point charge, with charge Q equal to

`Q=-9.0 nC=-9.0 \cdot 10^(-9)C`
We want to find the electric field at a distance
`d=2.4 cm= 0.024 m`. The electric field of a single point charge is given by

`E=k_e (Q)/(d^2)`
where
`k_e = 8.99 \cdot 10^9 N m^2 C^(-2)`
So, substituting, we find the electric field at the distance d:

`E=(8.99 \cdot 10^9 N m^2 C^(-2)) (-9.0\cdot 10^(-9)C)/((0.024m)^2)=-1.40\cdot 10^5 N/C`
And the negative sign means the field is directed towards the charge, since the charge is negative.