Physics 20 – Unit 4 Exam – Optics
Name_____________
December 20th , 2010
Part A. Match each of the statements from the first column with a lens in the second column.
Place the letter of the corresponding lens in the second column in the correct blank. Each part
is worth one mark.
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Image is always upright
Has a positive focal length
Produces virtual images
Parallel incident rays are refracted towards the principal axis
Has two focal points
Thick at the middle, thin at the ends
Thin in the middle, thick at the ends
Produces real images
Can produce an image with the same size as the object
Can produce an image that is smaller than the object
C. Converging
D. Diverging
B. Both
Part B. Solve the following Problems. Some questions require a diagram, some require math.
If the question does not specify then you get to choose. Each question varies in the amount of
marks it is worth.
1. Locate the images for the following objects:
a)
F
F
F
F
b)
2. Using a scale diagram, what is the height and distance of the image of a 18.0 cm tall
object placed 6.0 cm from a converging lens with a focal length of 12.0 cm?
3. Using math, calculate the magnification of an image in a converging lens if a 10.0 cm tall
object produces a real image 7.5 cm tall.
4. Using math, what is the focal length for a lens if an object 15.0 cm away produces a
virtual image 13.5 cm away? Is the lens converging or diverging?
5. An object is placed 30.0 cm from a diverging lens with a focal length of 20.0 cm. If the
object is 15.0 cm tall, what is the image height? Note that if drawing a scale diagram,
the scale or drawing of the lens will not be included in the marks (hence, only 6 marks).
Bonus (not for marks but to see if focus your thoughts)
A home-made T.V. projection system uses a large convex lens to cast the real image of the
screen onto a wall. The final picture is enlarged three times and, although rather dim, is nice
and clear. If the lens has a focal length of 60 cm, what should be the distance between the
screen and the wall? How should the screen be mounted with respect to the lens?
Merry Christmas! Have a safe holiday!