Using a Michelson Interferometer and a Light Source Of $400 \mathrm{~nm}$

Multiple Choice

Using a Michelson interferometer and a light source of $400 \mathrm{~nm}$ , a change from bright to dark indicates a change in the difference of arm lengths of

A) $1.0 \times 10^{-4} \mathrm{~mm}$ .
B) $4.0 \times 10^{-4} \mathrm{~mm}$ .
C) $2.0 \times 10^{-4} \mathrm{~mm}$ .
D) $3.0 \times 10^{-4} \mathrm{~mm}$ .