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When a wave strikes a boundary between media, some of its energy is reflected while some is transmitted. If the wave strikes the media at an angle, the transmitted wave will bend or move in a slightly different direction than the incident wave; the wave will **refract**!

The black lines in the image above represent the crests of the waves. The red line is the **media interface**, or the transition between media. How did the medium change? What happens to the speed of the waves when the waves hit the boundary? What does the yellow line represent?

In the following image, the dotted line is a normal line, perpendicular to the interface:

The **angle of incidence**, θ_{i}, is the angle between the incident ray and the normal line, as shown in the image above. Based on the definition of an angle of incidence, what is the **angle of refraction**, θ_{r}? How does it compare to the angle of incidence?

**Remember:** the relationship of the angles, velocities, and wavelengths at any media interface can be expressed in the following ratios:

\begin{align*}\frac{\sin\theta_r}{\sin\theta_i}=\frac{v_r}{v_i}=\frac{\lambda _r}{\lambda _i}\end{align*}

You can click here to find more information on the refraction of mechanical waves and to check your answers.