Light Refraction: Direction of Bend

[mmg0789]

For each of the following cases, will the light rays be bent toward or away from the normal?

a. ni > nr, where the angle of ni = 20
b. ni < nr, where the angle of ni = 20
c. from air to glass with an angle of incidence of 30
d. from glass to air with an angle of incidence of 30

for a, i put toward. b i think is away (but I'm not sure why it would be) and i am not sure about c and d

thanks in advance

 

[George Jones]

Do you know an equation that would help to answer these questions.

Regards,
George

 

[Hootenanny]

You are correct for a and b. Perhaps if you drew a diagram, it would make the answer more apparent. Where are the angles measured from?

As for c and d. Consider snell's law, what happens when a light ray travels through the interface from a lower refractive index (air) to a higher (glass) and visa versa.

~H

 

[mmg0789]

well i think this is a conceptual problem, so no equation is needed. but the equation i have to work with is (ni)(sinXi)=(nr)(sinXr)

--index of refraction of first medium x sine of the angle of incidence = index of refraction of second medium x sine sine of the angle of refraction

 

[mmg0789]

o ok thanks

 

[George Jones]

I find that that looking at a physics problem from different perspectives is often useful. As Hootenanny has indicated, diagrams here are very useful, but I like also to verfiy things with mathematics.

Note that the graph of sinx is increasing for x between 0 and 90, i.e., if sinx2 > sinx1, then x2 is greater than x1.

Now consider a) ni > nr. In order for ni sinXi = nr sinXr to hold, this means that sinXi < Sin Xr, which in turn, from what I wrote above, means that Xi < Xr. Now, a diagram shows what happens with respect to bending towards/ away from the normal.

Regards,
George

 

[mmg0789]

o thank you both