Why does ray a correspond to red and ray b to violet in this dispersion diagram?

[Augustine Duran]

Homework Statement

Rays a and b are shown in the figure. Which corresponds to red and which to violet?

The answer in mastering physics says that ray a corresponds to red. Why is this? I've read that colors with higher frequencies will bend more than those of lower frequencies. From what i can tell ray a is bending more so shouldn't a correspond to violet?

I was also looking through my book and found that violet colors have a higher index of refraction in silicate flint glass than do red ones. doesn't light with higher indexes bend more?

 

[ehild]

The angle of incidence (alpha) and the angle of refraction (beta) both are angles enclosed by the rays with the normal of incidence, the red line in the figure. You see that b bends more towards the normal after refraction.

 

[Augustine Duran]

is the reason your measuring the refraction angle from within the glass because the two rays seem to be parallel coming out of the glass?

 

[ehild]

is the reason your measuring the refraction angle from within the glass because the two rays seem to be parallel coming out of the glass?

Refraction happens to the rays at both sides of the glass. Leaving the glass, both rays have the same direction (they are parallel) only shifted.
Refraction means that the light ray, incident upon the interface between different media, will change direction. This change happens according to Snell's Law: n₁sin(α)= n₂ sin(β). If the ray is incident from air (refractive index n₁=1) at the surface of glass (refractive index n2) sin(β)=sin(α)/n₂. The angle of refraction changes more when the refractive index is higher.

 

[Augustine Duran]

So is it correct to say that both a and b are bending away from the normal at the RIGHT side of the glass at the same angle, that ray a is just shifted down?

 

[ehild]

So is it correct to say that both a and b are bending away from the normal at the RIGHT side of the glass at the same angle, that ray a is just shifted down?

Both rays, a and b are just shifted down with respect of the incident ray. The rays are bent away from the original direction inside the glass.