How does refraction change wave direction?

Refraction changes wave direction by bending the wave as it passes from one medium to another.

When a wave, such as light or sound, travels from one medium to another (like from air to water), its speed changes. This change in speed causes the wave to bend, a process known as refraction. The amount of bending depends on the angle at which the wave enters the new medium and the difference in speed between the two media.

Imagine a light wave hitting the surface of a glass of water at an angle. As the wave enters the water, it slows down because light travels slower in water than in air. This change in speed causes the light wave to bend towards the normal line (an imaginary line perpendicular to the surface). Conversely, if the light wave exits the water and re-enters the air, it speeds up and bends away from the normal line.

The degree of bending can be predicted using Snell's Law, which states that the ratio of the sine of the angle of incidence (the angle the incoming wave makes with the normal) to the sine of the angle of refraction (the angle the refracted wave makes with the normal) is constant and equal to the ratio of the speeds of the wave in the two media. Mathematically, this is written as:

\[ \frac{\sin(\theta_1)}{\sin(\theta_2)} = \frac{v_1}{v_2} \]

where \( \theta_1 \) is the angle of incidence, \( \theta_2 \) is the angle of refraction, \( v_1 \) is the speed of the wave in the first medium, and \( v_2 \) is the speed of the wave in the second medium.

Understanding refraction is crucial in many applications, such as designing lenses for glasses and cameras, and even in understanding natural phenomena like rainbows. By analysing how waves change direction when they move between different media, we can better understand and manipulate the behaviour of waves in various contexts.