The correct answer is
d. refracted
In fact, refraction occurs when light travels from one medium to another, and when it crosses the interface between the two mediums, light changes both its direction and its speed.
There is a mathematical relationship which allows us to calculate how much the direction and the speed change. It is called Snell's law, and it is the following:
\(n_1 \sin \theta_1 = n_2 \sin \theta_2\)
where n1 and n2 are the reffractive index of the first and second medium, while \(\theta_1, \theta_2\) are the angle of the light in the first and the second medium, measured with respect to the perpendicular to the interface between the two mediums.
The refractive index, instead, measure how much the speed of light changes in a medium. It is defined as follows:
\(n= \frac{c}{v}\)
where c is the speed of light in vacuum and v is the speed of light in that medium. If we know c and n, we can find the speed of light in that medium, v.
