Fused Quartz Has an Index of Refraction of 1

Multiple Choice

Fused quartz has an index of refraction of 1.55 for light from a 550-nm source.What is the speed of light for this wavelength within the quartz? (c = 3.00 × 10⁸ m/s)

A) 1.55 × 10⁸ m/s
B) 1.94 × 10⁸ m/s
C) 2.41 × 10⁸ m/s
D) 1.25 × 10⁸ m/s
E) ​1.45 × 10⁸ m/s