Question

PI 1: Qualitatively, why does a large radius of curvature give a large f? Qualitatively, why does a small index of refraction result in a large f? Use Snell’s law to in your discussion.  

PI 2: Qualitatively why is it that the light rays which strike the edge of the lens bend more than the light rays which strike the center of the lens? Your answer should explain how Snell’s Law is connected to the behavior of the Principal Rays.

PI 3: You should notice that the image never appears between the lens and the right focal point. Why is this? Use formula 3 to help explain why this cannot happen.

Formula 3: 1/f = (1/p) + (1/q)

Answer 1

Focus point is the point where all rays coming from infinity (parrallely) meet that's why large radius of curvature means

at small part lens it behaves as plane lens so, focul length must be very far so it is proportial to radius of curvature.

small refractive index means lower the bending of light at interface according to snell's law, so meeting of parralel light is far from interface so f is large.

2) A the edges light ray is reffracted through one portion of lens and radius of curvature shows discontounity so effective focal length changes drastically so that's why light bends more at edges. Snell's law gurantees that at the refractive index chanes discontinuously so, light bending is very large.

3) if image appear between the f and lens means q<f

in that case,

(1/p)=(1/f) -(1/q)

so,

(1/p)<0

p<0

means object is placed in back(imaginary) plane which is not possible