# Verify that the critical angle for light going from water to air is 48.6, as discussed at

## Question:

Verify that the critical angle for light going from water to air is 48.6°, as discussed at the end of Example 25.4, regarding the critical angle for light traveling in a polystyrene (a type of plastic) pipe surrounded by air.

**Data from Example 25.4**

What is the critical angle for light traveling in a polystyrene (a type of plastic) pipe surrounded by air?

**Strategy**

The index of refraction for polystyrene is found to be 1.49 in Figure 25.14, and the index of refraction of air can be taken to be 1.00, as before. Thus, the condition that the second medium (air) has an index of refraction less than the first (plastic) is satisfied, and the equation θ_{c} = sin^{-1} (n_{2}_{1}) can be used to find the critical angle θ_{c}. Here, then, n_{2} = 1.00 and n_{1} = 1.49.

**Data From Figure 25.14**

## Step by Step Answer:

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