Answer
a. 1.55.
b. 550nm.
Work Step by Step
a. $n=\frac{c}{v}=\frac{3.00\times10^8m/s }{1.94\times10^8m/s }=1.55$.
b. The wavelength in quartz is shorter by a factor of n. Find the wavelength in air.
$$\lambda_q=\frac{\lambda_0 }{1.55}=355nm $$
$$\lambda_0=(1.55)(355nm)=550nm$$
