The material with the lower refractive index has a higher critical angle.
Understanding Critical Angle
The critical angle is the angle of incidence at which light passing from a denser medium to a rarer medium is refracted at an angle of 90 degrees. This means the light travels along the boundary between the two mediums.
Here's a breakdown:
- Denser medium: A medium with a higher refractive index. Light travels slower in denser mediums.
- Rarer medium: A medium with a lower refractive index. Light travels faster in rarer mediums.
When light travels from a denser medium to a rarer medium, it bends away from the normal. As the angle of incidence increases, the angle of refraction also increases. At the critical angle, the angle of refraction reaches 90 degrees, and the light no longer enters the rarer medium. Instead, it undergoes total internal reflection.
Examples
- Water (n = 1.33) and air (n = 1.00): Water has a higher refractive index than air. Therefore, the critical angle for light passing from water to air is higher than the critical angle for light passing from air to water.
- Glass (n = 1.5) and water (n = 1.33): Glass has a higher refractive index than water. The critical angle for light passing from glass to water is higher than the critical angle for light passing from water to glass.
Practical Insights
- Fiber optics: The concept of critical angle is crucial in fiber optics. The core of an optical fiber has a higher refractive index than the cladding. Light is guided through the core by total internal reflection, which occurs because the angle of incidence at the core-cladding interface is always greater than the critical angle.
- Diamonds: Diamonds have a high refractive index, resulting in a high critical angle. This is why diamonds sparkle so brightly.
