Past a certain steepness, light hitting the inside of a glass surface stops escaping altogether and bounces back as if the surface were a perfect mirror. That tipping point is the critical angle, and the effect keeps light racing down fibre-optic cables.
When light travels from a denser to a less dense medium, increasing the angle of incidence reaches a critical angle at which the refracted ray runs along the surface. Beyond that angle, no light escapes: it is all reflected back, which is total internal reflection.
The critical angle is the angle of incidence in the denser medium for which the angle of refraction is 90 degrees; beyond it, total internal reflection occurs and all the light is reflected back.
It only happens going from a denser to a less dense medium, such as glass to air.
Increase the angle of incidence inside the glass and watch the refracted ray vanish as the light is reflected back.
A right-angle glass prism turns light through 90 degrees by total internal reflection. The ray meets the slanted face at 45 degrees, more than the critical angle, so none of it escapes. Two such prisms form a periscope.
Four quick checks. Each correct answer earns XP and lights this skill on your star map.
The critical angle is the angle of incidence for which the angle of refraction is...
Total internal reflection occurs when the angle of incidence is...
Total internal reflection can occur when light passes from...
When the angle of incidence is greater than the critical angle, the light is...
As the angle of incidence grows, the behaviour passes through three clear stages.
Total internal reflection only happens when light travels from a denser to a less dense medium, such as glass to air, and only when the angle of incidence is greater than the critical angle. Light going from air into glass can never be totally internally reflected.
Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 2.
Light inside a glass block meets the glass-air boundary at an angle larger than the critical angle. It will...
At exactly the critical angle, the refracted ray...
Total internal reflection can NOT occur when light travels from...
Total internal reflection mastered. The Extended look at refractive index is next.