A light ray of wavelength lambda = 510. nm enters at an angle of incidence of 35.4 degrees from air into a block of plastic. Its angle of refraction is 20.3 degrees. What is the speed of the light inside the plastic?
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the speed of light in a refractive medium is c/n where c is the speed of light in a vacuum and n is the refractive index
so we find the refractive index from snell's law
n1 sin(theta1) = n2 sin(theta2)
n1=1 (air), we find n2
1 x sin 35.4 = n2 sin 20.3
n2 = sin 35.4/sin 20.3 = 1.67
speed in block = 3x10^8m/s / 1.67 = 1.8x10^8m/s
so we find the refractive index from snell's law
n1 sin(theta1) = n2 sin(theta2)
n1=1 (air), we find n2
1 x sin 35.4 = n2 sin 20.3
n2 = sin 35.4/sin 20.3 = 1.67
speed in block = 3x10^8m/s / 1.67 = 1.8x10^8m/s