| Term | Definition |
|---|---|
| Normal | A straight line that is perpendicular to the surface at the point of incidence. Think of it as the “ground line” when a ball bounces off a wall. |
| Angle of Incidence | The angle between the incident ray and the normal. It’s like the angle at which a skateboarder lands on a ramp. |
| Angle of Refraction | The angle between the refracted ray and the normal. Imagine the skateboarder sliding off the ramp at a new angle. |
When light moves from one medium to another (e.g., air to water), it bends because its speed changes. The relationship is described by Snell’s law:
\$n1 \sin \theta1 = n2 \sin \theta2\$
Where \$n1\$ and \$n2\$ are the refractive indices of the first and second media, \$\theta1\$ is the angle of incidence, and \$\theta2\$ is the angle of refraction.
\$\sin \theta2 = \frac{n1}{n2} \sin \theta1 = \frac{1.00}{1.33} \sin 30^\circ = 0.375\$
\$\theta_2 = \sin^{-1}(0.375) \approx 22^\circ\$
So the light bends towards the normal, ending up at about \$22^\circ\$.
Remember: the normal is the “reference line”; the angle of incidence is measured from this line to the incoming ray; the angle of refraction is measured from the normal to the outgoing ray. By keeping these angles straight, you can predict how light will bend at any interface.