Light changes direction slightly when passing from one substance to another?

This phenomenon is known as Refraction.

Explanation:

Light waves change speed when they pass across the boundary between two substances with a different density, such as air and glass. This causes them to change direction, an effect called refraction.

At the boundary between two transparent substances:

the light slows down going into a denser substance, and the ray bends towards the normal

the light speeds up going into a less dense substance, and the ray bends away from the normal

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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