The electric field produced by a uniformly charged sphere is equal to that produced by a single point charge:
[tex]E(r)=k_e \frac{Q}{r^2} [/tex]
where
[tex]k_e = 8.99 \cdot 10^9 Nm^2 C^{-2}[/tex] is the Coulomb's constant
Q is the charge of the sphere
r is the distance at which we calculate the field strength
The glass bead of our problem has a charge of [tex]Q=+5.0 nC=+5.0 \cdot 10^{-9} C[/tex], and if we use the previous formula we can calculate the electric field strength at distance [tex]r=3.0 cm=0.03 m[/tex] from the bead:
[tex]E=(8.99 \cdot 10^9 Nm^2C^{-2}) \frac{5 \cdot 10^{-9}C}{(0.03 m)^2}=5 \cdot 10^4 N/C [/tex]
