Question

What is the strength of the electric field 3.0 cm from a small glass bead that has been charged to + 5.0 nc ?

Answer 1

The electric field produced by a uniformly charged sphere is equal to that produced by a single point charge:

`E(r)=k_e (Q)/(r^2)`
where

`k_e = 8.99 \cdot 10^9 Nm^2 C^(-2)` 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
`Q=+5.0 nC=+5.0 \cdot 10^(-9) C`, and if we use the previous formula we can calculate the electric field strength at distance
`r=3.0 cm=0.03 m` from the bead:

`E=(8.99 \cdot 10^9 Nm^2C^(-2)) (5 \cdot 10^(-9)C)/((0.03 m)^2)=5 \cdot 10^4 N/C`