Example 22.2 Angle of Refraction for Glass
Goal Apply Snell's law to a slab of glass.
Problem A light ray of wavelength 589 nm (produced by a sodium lamp) traveling through air is incident on smooth, flat slab of crown glass at an angle of Ģā = 30° to the normal, as sketched in Figure 22.11. Find the angle of refraction, Īøā.
Strategy Substitute quantities into Snell's law and solve for the unknown angle of refraction, Īøā.
Solution
Solve Snell's law (Eq. 22.8) for sin Īøā
sinĪøā = (nā/nā)sinĪøā (1)
From Table 22.1, find nā = 1.00 for air and nā = 1.52 for crown glass. Substitute these values into (1) and take the inverse sine of both sides.
sinĪøā = (1.00 / 1.52)(sin30.0°) = 0.329
Īøā = sinā»Ā¹(0.329) =
Remarks Notice the light ray bends toward the normal when it enters a material of a higher index of refraction. If the ray left the material following the same path in reverse, it would bend away from the normal.
Exercise 22.2
If the light ray moves from inside the glass toward the glass-air interface at an angle of 30.0° to the normal, determine the angle of refraction.
The ray bends ° away from the normal, as expected.