Electrostatics
Intermediate
Electric Field
Source: High school physics (Chinese)
Problem Sets:
Electrostatics
Problem
An amount of $2 \times 10^{10}$ electrons are added to a small object.
- What is the magnitude of the electric field at a distance of 0.3 m from this object?
- What is its direction?
E = 320 N/C, directed towards the object.
The total charge $Q$ is the number of electrons $n$ multiplied by the elementary charge $-e$. The object is treated as a point charge. The electric field magnitude $E$ is given by Coulomb's law.
$$Q = n(-e)$$ $$E = k \frac{|Q|}{r^2} = k \frac{ne}{r^2}$$Since the object has an excess of electrons, its net charge is negative. The electric field produced by a negative charge points radially inward, towards the charge.