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Physics/Refraction of light


Recently I was going through a book where a statement regarding the refraction of light was given as follows:
"The cause for refraction is due to the change in speed of light as it passes from one medium to another. For normal incidence there occurs a change in the speed of light,but light passes undeviated."
Why is then there no bending of the ray of light during normal incidence?

ANSWER: Due to the geometry of waves and the change in the wave speed between the two mediums, the light will bend either towards or away from the normal to the surface.  This is sharper at higher angles (Snell's law) from the normal, and goes to zero at normal incidence.  To put it another way, at normal incidence there is no direction for it to bend towards or away from because there is no angle between the direction of the light and the normal vector.

---------- FOLLOW-UP ----------

QUESTION: Thank you sir for your answer. I really loved it. But could you please tell me what geometry of waves is responsible for refraction?

Any periodic wave with a characteristic wavelength should refract.  For more graphical representations, see here: and here: and here:

For that last one, you might want to research Huygens' principle.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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