# A Refraction of Light Question : Why Does Diamond Sparkle More? (Ans. )

1. Dec 4, 2007

### incognito301

***** A Refraction of Light Question : Why Does Diamond Sparkle More? (Ans. ASAP plz)

Diamond has a critical angle of 24 degrees. Crown glass has a critical angle of 42 degrees. Why does a diamond sparkle more in bright light than a piece of crown glass, even with the equivalent shape?

The light rays only reflect when their angles of incidence is less than the critical angle (I think!). 42 > 24, so diamond should let more light refract (or pass through and not reflect. So it should shine less! That's not what the question says!

Help me out ASAP plz.

2. Dec 4, 2007

### dynamicsolo

I believe you are forgetting the definition of critical angle. The angles for refraction are measured from the perpendicular (or normal) to the surface. So light within the diamond cannot pass back out into the air unless it is closer to the perpendicular than 24º (or making an angle to the surface greater than 66º). Any ray making a shallower angle to the surface will undergo total internal reflection and stay within the crystal.

A substantial part of the art of gem-cutting is to bevel the facets of the crystal so that light rays will undergo internal reflection as long as possible, thus making the gem the most effective possible light-trap.

Last edited: Dec 4, 2007