How fast does light travel through gelatin?

Answer 1

The speed of light through Jell-O.

Photons generated by a laser are exactly the same -- go at the same speed, etc. -- as photons of the same color from any other source.

There are two different paths a photon can take through Jell-O:

(1) Most colors of photons will go more or less straight through.

Since Jell-O is mostly water, those photons go at pretty close to the speed of light through water -- this is somewhat slower than the speed of light through a vacuum (often abbreviated as "the" speed of light, "c").

The refractive index of water is 1.33, meaning that light travels 1.33 times faster in a vacuum than it does in water.

In vacuum, light travels roughly 1 foot (0.3 meters) per nanosecond.

In water, light travels roughly 3/4 foot (0.2 meters) in the same nanosecond.

(2) Some colors of photons may take *much* longer.

Some flavors of Jell-O are fluorescent.

When you shine light on fluorescent Jell-O, the dye molecules absorb a few photons of *some* colors, and then a relatively long time later release photons (often of a different color).

After you turn off the lights, photons continue to trickle out for a relatively long time (a few microseconds are a long time for this sort of thing).

If you pulse the light on-off, the first batch of "fast" photons gets through very quickly, and then sometime later the "slow" photons trickle out.

Answer 2

It varies according to the sample, but refractive indices in the range 1.3-1.5 are typical (see the linked paper for an example).

Assuming a refractive index of around 1.5:

Speed of light in medium= (Speed of light in vacuum) / (Refractive index)= (3 × 108 m s-1) / (1.5)

= 2 × 108 m s-1 to one significant figure.