Write $0.0002$ in scientific notation:

$0.0002 = 2 \times 10^{-4}$

Raise to the $n$th power:

$(0.0002)^n = (2 \times 10^{-4})^n = 2^n \times (10^{-4})^n = 2^n \times 10^{-4n}$