4.06 Internal Reflections

The inside surface of _ materials can act like a perfect mirror.

• Translucent

• Transparent

• Opaque

If light strikes the surface at a greater angle than the critical angle :

• The ray splits, but the refracted ray only just travels along the surface.

• The ray spits into a refracted ray and a weaker reflection.

• There is no refracted ray, but a total internal reflection takes place.

If light strikes the surface at a lower angle than the critical angle :

• The ray splits, but the refracted ray only just travels along

  the surface.

• The ray spits into a refracted ray and a weaker reflection.

• There is no refracted ray, but a total internal reflection takes place.

If light strikes the surface at the critical angle :

• The ray splits, but the refracted ray only just travels along the surface.

• The ray spits into a refracted ray and a weaker reflection.

• There is no refracted ray, but a total internal reflection takes place.

The value of the critical angle depends on the _.

Why do the inside surface of this glass prism act like a perfect mirror?

• Because light is striking them at 45 deg. (more than critical angle)

• Because light is striking them at 90 deg. (less than critical angle)

• Because light is striking them at 41 deg. (same as critical angle)

Features of optical fibre:

• Thick, stiff rods of colored glass

• Thin, stiff rods of colorless glass

• Thin, flexible rods of opaque plastic

• Thin, flexible rods of colorless glass or transparent plastic.

• Thick, flexible rids of transparent plastic

Light put in at one end of the optical fibre is:

• Reflected from side to side

• Goes straight through

Examples of of the practical uses of optical fibre:

• Telephone calls are carried by optical fibres.

• Rear reflectors on cars contain bundles of optical fibre.

• Endoscopes contains a long, thin bundle of optical fibres.

• Prisms are made of optical fibres.