Refraction and Snell's Law

1
The focusing of a parallel beam of light to a
focus
is reversible
2
3 easy to trace lines can help locate the image
formed by a lens
p
f
f
q
q
M
p
With the magnification,
3
1
2
3
f
f / 2
4
5
The ray entering this diverging lens, parallel
to its axis, exits the other side following
which ray?
4
The divergence by a concave lens should be
reversible as well!
5
1
2
3
f
f / 2
4
Which ray entering the diverging lens exits the
other side parallel to its axis?
5
6
3 easy to trace lines can help locate the image
formed by a lens
p
f
q
f
q
M
p
With the magnification still,
7

When viewing objects by eye, which variable(s)
of the lens equation must always remain fixed?

1. the focal length, f
2. the object distance, p
3. the image distance, q

(4)both f and p (5)both f and q (6)both p and q
8
For everyone there is a NEAR POINT, the closest
position you can focus on
f
Any closer, the lens cannot accommodate. The eye
strains to hold f this small.
9

ho
q
p
The retinal image size must be proportional to

1. the focal length, f of the lens
2. the object distance, p
3. the image distance, q

(4)the object size, ho (5)both p and q (6)both p
and ho
10
ho
q
?
?
11
A jeweler whose near point is 40 cm, examines a
diamond with a small magnifying glass. The lens
has a focal length of 5 cm and the image is -185
cm from the lens.

• Determine the angular magnification.
• Where should the image be located for
• viewing without eyestrain?
• What is the magnification then?
• c)What maximum magnification is possible?

12
A jeweler whose near point is 40 cm, examines a
diamond with a small magnifying glass. The lens
has a focal length of 5 cm and the image is -185
cm from the lens.

• Determine the angular magnification.
• b)Where should the image be located for
• viewing without eyestrain?
• What is the magnification then?
• c)What maximum magnification is possible?

Want q-? , so 1/q 0 ?
When q-N ?
13
Some answers
2
Directed away from the focus on far side.
2
Directed toward the focus on near side.
(3) the image distance, q