Physics 106, Summer 2012
Reading: Chapters 23, Sec. 7-9
Did you complete the reading assignment?
Did you complete the entire quiz or spend at least 15
minutes working on this quiz and the attached links?
1) Lenses and mirrors
create images by converging or diverging light rays.
2) Ray diagrams predict the position and
magnification of an image.
3) Virtual images are behind a mirror or
4) Real images are in front of a mirror or
Go to the following link and use the applet at the top of the forum:
There are several different variables on the applet that you can change. To make
the the affects you are looking for easiest to see: change the lens size (left
side top scroll bar) to the smallest it can be, change the ray line spacing
(left side under the change lens scroll bar) to about the middle setting, and
the lens distance (top side scroll bar) closer to the left side than the right
side. Leave the 'n(outside)' value at 1.00, this means that you will be looking
at the ray lines going through air which is what you will focus on in class.
Increase the 'left curvature' by moving the scroll bar to the right. What kind
of lens does this make?
As the curvature of the lens gets larger, will the focal point be closer or
farther from the lens?
Increase the 'n(inside)' value. As the index of refraction of the lens gets
larger, will the focal point be closer or farther from the lens?
Go to this link:
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=48. The applet that you
will use pops up in a small window, it is not on the forum.
You can change a lot of stuff on this applet. You can change the image height
and position by clicking and dragging. The focal point is the red mark closest
to the lens on each side. You can also change any of the values at the top by
typing them in; the p is object position from the lens, the q is image position
from the lens, the f is the focal distance, and the M is the magnification. We
are going to keep it pretty simple, but if you want to try some more things,
especially if you have a hard time understanding ray diagrams it will be helpful
Which of the following is not a ray used in a ray diagram for finding the image
height and position of the object?
From top of image, perpendicular to the lens
until it gets to the lens, and through the far focal point.
From the top of the image, to the center of
the lens, and through the far focal point.
From the top of the image through the center
of the lens.
From the top of image, through the near focal
point until it gets to the lens, and perpendicular to the lens.
Move the position of the lens back and forth watching the magnification. For
this lens, a virtual image cannot be:
Larger than the object
Smaller than the object
Right side up
Move the image well inside the focal length of the lens. For a lens, a real image is:
Larger than the object and upright.
Smaller than the object and upright.
Larger than the object and upside down.
Smaller than the object and upside down.
Is this lens concave or convex. How do you know?
The lens is concave. The easiest way to tell is that it is possible to make a real image with the lens, which cannot be made with a convex lens.
Change the lens to a mirror in the scroll down box.
Move the position of the lens inside the focal point. For a concave mirror, a
virtual image is:
Move the position of the lens outside the focal point. For a concave mirror, a
real image cannot be:
Additionally, here is a game you can play if you are bored and want some
practice on understanding the affect mirrors have on image appearance:
The comments entered in these last two boxes go into a big anonymous data file that I will use to guide the lectures of the day. That means two things:
1) If you have a specific question or concern and would like an individual
answer you will need to come by the office or send an email.
2) If you really want to get an anonymous comment to me before the lecture, it
must be submitted before 11am that day.
Was there anything that you didn't understand in the reading assignment?
What was confusing to you?