PLC Activity #8
Lenses
Due: See website for due date
How to get credit for this activity
First, sign-in at the computer and sign-out when the activity is complete. Show your work and
results to a PLC tutor so they can check your work and initial the signoff sheet. Be prepared to
answer questions about the activity or your results.
Part 1: Lens Physlets
Physlet Problem 35.2
Four regions are hidden by curtains. The light sources are dragable. The arrow represents an
object, and the fainters arrow represents its image (position is given in meters).
a. What is behind each curtain?
b. Rank the objects in terms of their focal lengths, from smallest to largest (most negative to
most positive).
Physlet Problem 35.8
A light source is located to the left of two lenses (position is given in cm). You can click-drag
either lens through a limited range of x positions. Find the focal length of each lens.
Physlet Problem 35.11
Light rays from a point source, initially in air, are incident on a lens made from a material with an
index of refraction of 2.5 (position is given in cm). The radius of curvature of theleft side of the
lens is -10 cm (10-cm radius and concave, so rays diverge upon entering it). You can change
the radius of the right side. Build a lens so that the light rays from the point source will converge
on the green screen.
a. What is the focal length of this lens?
b. Calculate the radius of curvature of the right side of the lens, then test your claculation.
3-1
Part 2: Ranking Problems
Question 1
The table details six variations of the basic arrangement of two thin
lenses represented in the figure. An object is distance p1 to the left of lens
1. (a) For which variations can we tell, without calculation, whether the
final image (that due to lens 2) is to the left or right of lens 2 and whether
it has the same orientation as the object? (b) For those “easy” variations, give the image
location as “left” or “right” and the orientation as
Variation
Lens 1
Lens 2
“same” or “inverted.”
1
2
3
4
5
6
Converging
Converging
Diverging
Diverging
Diverging
Diverging
Converging
Converging
Converging
Converging
Diverging
Diverging
p1 < |f1|
p1 > |f1|
p1 < |f1|
p1 > |f1|
p1 < |f1|
p1 > |f1|
Question 2
In the figure, stick figure O stands in front of a lens that is mounted
within the boxed region. The four stick figures I1 to I5 suggest general
locations and orientations for the images that might be produced by
the lens (not to scale). (a) Which if the stick figures could not possibly
represent images? Of the possible images, (b) which would be due to a converging lens, (c)
which would be due to a diverging lens, (d) which would be virtual, and (e) which would involve
negative magnification? Explain your reasoning.
Question 3
Use precise language to describe the image characteristics (image location relative to f and 2f,
magnification) for the following photos A through E.
Question 4
The figure shows four thin lenses, all of the same material, with sides
that either are flat or have a radius of curvature of magnitude 10 cm.
Without written calculation, rank the lenses according to the magnitude
of the focal length, greatest first.
3-2