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# Physics and dispersion of light watch

1. As attached.

Bit stumped with this question............

I know that in order to determine N; SinAir/SinMedium =Refractive Index.

I know that violet > red; ergo, given that the refractive index of red here is identified as being 1.51; the refractive index of blue must exceed this value.

I know that x (the 0.7 degrees) is the angle of minimum deviation.

Given that we have sinAir, and the refractive index (for red) this meant then, that in order to find the value sinMedium:

sin40/1,51=0.4256
invert sine of 0.4256 =25.194 degrees

25.194-0.7=24.49 degrees

Therefore, refractive index of blue would be sin40/sin24.49 =1.55

But the answer is given as 1.54. I don't mean to be pedantic, but I want to be absolutely clear that I have gotten the technique right at least........

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