Step 1: Understanding the electric field between conducting plates.
For two infinite conducting plates with opposite charge densities \( +\sigma \) and \( -\sigma \), the electric field between them is given by:
\[
E = \frac{\sigma}{\epsilon_0}
\]
This is the field produced by one plate. Since both plates contribute to the electric field, the total electric field between them is twice this value. Hence, the total electric field is:
\[
E = 2 \times \frac{\sigma}{\epsilon_0}
\]
Step 2: Conclusion.
The value of \( n \) is 2.