The electric field between two parallel metal plates is given by
[tex]E= \frac{V}{d} [/tex]
where
E is the electric field
V is the voltage across the two plates
d is the separation between the two plates.
In our problem, the voltage is [tex]V=12 V[/tex] while the separation between the plates is [tex]d=0.30 cm=0.003 m[/tex], therefore the magnitude of the electric field is
[tex]E= \frac{V}{d}= \frac{12 V}{0.003 m}=4000 V/m [/tex]
