Welcome Guest Search | Active Topics |

Tag as favorite
Thin lens equation question AAMC
Options
Previous Topic Next Topic
Chloe_2125
#1 Posted : Saturday, June 19, 2021 5:53:22 AM
Rank: Newbie

Groups: Registered
Joined: 4/18/2021
Posts: 4

Thanks: 0 times
Was thanked: 0 time(s) in 0 post(s)
Hi,

I am really having a hard time understanding how to approach the following question from the AAMC full length 1. I tried to use the "foil" (1/f=1/o +1/i) equation but I can't seem to get to the correct answer (B). Are you able to explain how to best solve this one?

O
^
__|______.__(.)
3F F

In the above figure, an object O is at a distance of three focal lengths from the center of a convex lens. What is the ratio of the height of the image to the height of the object?

A.1/3
B.1/2
C.2/3
D.3/2


Thank you in advance :)
Back to top
Report?
INSTR_Katrina_128
#2 Posted : Tuesday, June 22, 2021 8:50:53 PM
Rank: Advanced Member

Groups: Registered
Joined: 5/18/2021
Posts: 73

Thanks: 0 times
Was thanked: 0 time(s) in 0 post(s)
Oooh let me give it a shot!

Subbing everything into the FOIL equation, we get

1/f = 1/o + 1/i
1/f = 1/(3f) + 1/i

Solve for 1/i:

1/i = 1/f - 1/(3f)

Get a common denominator.

1/i = 3/(3f) - 1/(3f)

Add.

1/i = 2/(3f)

Flip both sides.

i = 3/(2f) = 1.5f

They're asking about "the ratio of the height of the image to the height of the object" which is LITERALLY the definition of magnification. 😁 So...

m = -i/o
m = -1.5f / (3f)
m = -0.5

The sign tells us that the image is inverted, but the question doesn't care about that.

The best answer is B.
Back to top
Report?
Users browsing this topic
Guest
Tag as favorite
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.

Clean Slate theme by Jaben Cargman (Tiny Gecko)
Powered by YAF | YAF © 2003-2009, Yet Another Forum.NET
This page was generated in 0.043 seconds.