Q13DQ - University Physics with Modern Physics

Question

 A glass windowpane with a thin film of water on it reflects less than when it is perfectly dry. Why

Step-by-Step Solution

Answer

Due to the destructive interference between the reflected wave and film of water, a glass windowpane with a thin film of water on it reflects less than when it is perfectly dry 

Step 1: Define the principle of superposition.

Destructive interference can only occur if the difference in path travelled by the two waves is a half-integral multiple of the wavelength of light.

Step 2: Explain the reason for glass windowpane with a thin film of water on it reflects less than when it is perfectly dry

As the destructive interference occurs between the waves reflected from the top of the thin film of water (black) and the waves reflected from the glass window pane (red).   

                                                               

Hence, a glass windowpane with a thin film of water on it reflects less than what it would have been when it is perfectly dry.