Name PROBLEM 2-8 points You have an unknown optical device (either a mirror or a lens) that you are trying to identify. To do so you make the following observations. [2 points] (a) You observe that when you place an object at one particular distance in front of the device, the device creates a virtual image of the object. Based on this observation, what could te device be? Select all that apply I a concave (converging) mirror I 1 a convex (diverging) mirror I a convex (converging) lensa concave (diverging) lens aplane mirror 2 points] (b) You then observe that the image is upright compared to the object, and that the image is smaller than the object. Based on this and the previous observation, what could the device be? Select all that apply I [ ] a convex (diverging) mirror a concave (converging) mirror I a convex (converging) lensa concave (diverging) lens aplane mirror [1 point (c) You then observe that the smaller upright image is on the opposite side of the device as the object. Based on this and the previous observations, what is the device? I a concave (converging) mirror [ ] a convex (diverging) mirror I a convex (converging) lensa concave (diverging) lens aplane mirror [1 point] (d) The device has a focal length with a magnitude of 30 cm, and the object distance is 15 cm. Calculate the image distance. [2 points (e) Draw the device on the diagram below and then sketch a ray diagram for the situation described in part (d). The tick marks on the diagram are 5 em apart. location of the s or miror object Solution (a) All All the optical devices are capable of creating a virtual image. (b) concave(diverging) lens and convex(diverging) mirror All virtual images are upright. The factor to consider is the height. The image is smaller. The virtual image of plane mirror is always the same size as the object; of convex lens and concave mirror are larger. Only for concave lens and convex mirror, the image is smaller than the object. (c) Convex (diverging) mirror We are left with two options: concave lens and convex mirror. In this part we are given the info that the image is formed on the opposite side. For concave lens, the image is formed on the same side while for convex mirror it is formed on the opposite side. Thus the device is convex mirror. (f) Given: f = -30 cm (f is negative for concave mirror) u = 15cm Use mirror eqn: 1/f = 1/u + 1/v => 1/v = 1/f - 1/u => 1/v = (1/-30) - (1/15) => v = -10cm (- sign means that the image is formed on the opposite side) Thus the image is 10cm on the opposite side of the mirror. .

1. Name PROBLEM 2-8 points You have an unknown optical device (either a mirror or a lens) that
you are trying to identify. To do so you make the following observations. [2 points] (a) You
observe that when you place an object at one particular distance in front of the device, the device
creates a virtual image of the object. Based on this observation, what could te device be? Select
all that apply I a concave (converging) mirror I 1 a convex (diverging) mirror I a convex
(converging) lensa concave (diverging) lens aplane mirror 2 points] (b) You then observe that the
image is upright compared to the object, and that the image is smaller than the object. Based on
this and the previous observation, what could the device be? Select all that apply I [ ] a convex
(diverging) mirror a concave (converging) mirror I a convex (converging) lensa concave
(diverging) lens aplane mirror [1 point (c) You then observe that the smaller upright image is on
the opposite side of the device as the object. Based on this and the previous observations, what is
the device? I a concave (converging) mirror [ ] a convex (diverging) mirror I a convex
(converging) lensa concave (diverging) lens aplane mirror [1 point] (d) The device has a focal
length with a magnitude of 30 cm, and the object distance is 15 cm. Calculate the image distance.
[2 points (e) Draw the device on the diagram below and then sketch a ray diagram for the
situation described in part (d). The tick marks on the diagram are 5 em apart. location of the s or
miror object
Solution
(a) All
All the optical devices are capable of creating a virtual image.
(b) concave(diverging) lens and convex(diverging) mirror
All virtual images are upright. The factor to consider is the height.
The image is smaller.
The virtual image of plane mirror is always the same size as the object; of convex lens and
concave mirror are larger.
Only for concave lens and convex mirror, the image is smaller than the object.
(c) Convex (diverging) mirror

2. We are left with two options: concave lens and convex mirror.
In this part we are given the info that the image is formed on the opposite side.
For concave lens, the image is formed on the same side while for convex mirror it is formed on
the opposite side. Thus the device is convex mirror.
(f)
Given: f = -30 cm (f is negative for concave mirror)
u = 15cm
Use mirror eqn:
1/f = 1/u + 1/v
=> 1/v = 1/f - 1/u
=> 1/v = (1/-30) - (1/15)
=> v = -10cm (- sign means that the image is formed on the opposite side)
Thus the image is 10cm on the opposite side of the mirror.