Physics/Optics/Principles and Exploration
Refraction and total internal reflection — principles and investigation
The phenomenon in which objects in water appear bent occurs because light changes direction at the boundary of the medium. Compare the refraction angles by changing the refractive index and normal incident angle of the two media. The key is to first determine the direction in which total reflection is possible and then observe the front and back of the critical angle.
How does it work?
When the refractive index goes toward the higher side, it bends toward the normal line. When going from a large refractive index to a small refractive index, if the critical angle is exceeded, it is total reflection.
n₁sinθ₁ = n₂sinθ₂
Try this investigation
- Drag the light source or change the slider to measure the angle relative to the normal. Observe light rays by running an experiment.
- In air → glass, record the angles of incidence 0°, 30°, and 60°.
- Record the refractive index conditions before and after the critical angle for water → air.
Interpreting your results
What are the conditions under which total reflection is possible?
sinθc=n₂/n₁, and there is a critical angle only when n₁>n₂.
Assumptions and limitations
It is a monochromatic geometric optical model with a flat boundary. Dispersion, absorption, polarization, Fresnel reflectance, and evanescent wave are omitted. The protractor is based on the normal, and the ray only shows direction. At the critical angle, the refraction angle is 90°, and at angles larger than that, it is processed by total reflection.