Physics

Physics

Problem

The frequency of an electromagnetic wave in a glass block of refractive index n=1.5n = 1.5 is 6×1014 Hz6\times10^{14}\,\text{Hz}. Calculate its wavelength inside the glass. a) 5.0×10−7 m5.0\times10^{-7}\,\text{m} b) 7.5×10−7 m7.5\times10^{-7}\,\text{m} c) 3.3×10−7 m3.3\times10^{-7}\,\text{m} d) 2.2×10−7 m2.2\times10^{-7}\,\text{m}
Intuitive explanation

The key insight is that frequency never changes when light enters a new medium—only wavelength and speed do. Since you know the frequency in glass, you need to find the wave speed there using the refractive index, then apply the wave equation v=fλv = f\lambda. The refractive index tells you how much slower light travels in glass compared to vacuum, so use v=c/nv = c/n to find the actual speed inside the material.

Intuitive explanation

The key insight is that frequency never changes when light enters a new medium—only wavelength and speed do. Since you know the frequency in glass, you need to find the wave speed there using the refractive index, then apply the wave equation v=fλv = f\lambda. The refractive index tells you how much slower light travels in glass compared to vacuum, so use v=c/nv = c/n to find the actual speed inside the material.

Browse the problem library