Having trouble finding the angle of deflection of light

[kliker]

we have this picture

http://img190.imageshack.us/img190/1128/60283381.jpg

how can i find the angle of deflection?

i must show that it is: sin(A+δ)/2 = n*sinA/2

 

[kuruman]

You need to apply Snell's Law at the the two interfaces. Note that since the incident angle with respect to the normal is the same as the exit angle with respect to the normal, symmetry demands that the ray travel parallel to the base inside the prism. Assume that the prism angle (at top) is known because the angle of deflection depends on it.

 

[kliker]

You need to apply Snell's Law at the the two interfaces. Note that since the incident angle with respect to the normal is the same as the exit angle with respect to the normal, symmetry demands that the ray travel parallel to the base inside the prism. Assume that the prism angle (at top) is known because the angle of deflection depends on it.

thanks but how can we know if the incident angle with respect to the normal is the same as the exit angle?

it doesn't say anything like that, how can we assume this

also

i applied snell but i have sina/sinb = n and sinc/sind = 1/n

also i have proven that A = b + c

http://img130.imageshack.us/img130/6987/50944329.png

im having trouble finding that sin(A+δ)/2 = n*sinA/2 :(

thank you again

 

[kuruman]

As best as I can say from your posted diagram at

http://img190.imageshack.us/img190/1128/60283381.jpg

both incident and exit angles are labeled θ_a. Is this not true?

 

[kliker]

no I think the second one is θb where b = β(the greek letter)

 

[kliker]

if we supposed that it is the same how could we reach the desired solution?

 

[ehild]

Referring to your drawing, it is easy to find that the deflection is a+d-A.
The formula you have to prove is valid only for the minimal deflection. The deflection is minimal when the incident and the exit rays are symmetrical: a=d.

ehild

 

[kliker]

ok guys i figured everything out

the teacher made a mistake it was θα the second one too, it was easy to solve i thought they were different

thanks everyone