Lenses - magnification, position, focal length help

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Homework Help Overview

The discussion revolves around a problem involving lenses, specifically focusing on magnification, image position, and focal length. The original poster presents a scenario where an object is placed 3.5 cm from a lens, producing an image with a magnification of +0.667. Participants are exploring whether the lens is diverging or converging and how to calculate the image position and focal length using relevant equations.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the nature of the lens and its classification as diverging or converging. They explore the magnification equation and its application, questioning how to derive the object height and image distance. There are inquiries about the thin lens equation and how to incorporate the known values into it.

Discussion Status

The discussion is active, with participants attempting to clarify their understanding of the equations involved. Some have made progress in calculating magnification and discussing the lens equations, while others express confusion about how to proceed with the calculations. There is a recognition of having two equations and two unknowns, indicating a productive direction in the exploration of the problem.

Contextual Notes

Participants note the urgency of the assignment due date and the requirement to show effort before receiving further assistance. There is a mention of needing to create a diagram as part of the problem, which adds to the complexity of the task.

alicia113
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Lenses - magnification, position, focal length help!

ok so here is the quesiton..

An object is loacted 3.5 cm from the optical centre of a lens. The lense produces an image of magnification that is +0.667 the size of the object

a) is this lens a diverging or converging lens? explain

b) Find the position of the image and the focal length of the lens using the magnification equation and the thin lens equation

c) make a diagram of the situation, showing the axis of symmetry and the prinicple axis of the lens, its optical centre itrs principle focal points and the positions of the object and image



ok so you said it was a diverging lens and i have NO IDEA how to do b... i am going back and back to my notes... but i just don't understand :confused: ... someone please help me ! this is due tomorrow too :cry:
 
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alicia113 said:
ok so here is the quesiton..

An object is loacted 3.5 cm from the optical centre of a lens. The lense produces an image of magnification that is +0.667 the size of the object

a) is this lens a diverging or converging lens? explain

b) Find the position of the image and the focal length of the lens using the magnification equation and the thin lens equation

c) make a diagram of the situation, showing the axis of symmetry and the prinicple axis of the lens, its optical centre itrs principle focal points and the positions of the object and image



ok so you said it was a diverging lens and i have NO IDEA how to do b... i am going back and back to my notes... but i just don't understand :confused: ... someone please help me ! this is due tomorrow too :cry:

Welcome to the PF.

Per the PF rules, you need to show some effort before we can be of tutorial help.

What do you mean "you said it was diverging"? Who is you?

A good place to start is to list the lens equations, and show how you calculate magnification. Then try to make the sketch they are asking for -- that should get you pretty far along... Please show us your work.
 


So magnification is


M= hi/ho = -di/do
 


So hi is +3.5cm. But what's the ho?

M=3.5/? = +0.667

So it would end up being 3.5/0.667 = 5.24? Am I correct?
 


Good so far. Sketch?
 


Is there an equation for focal length.?
 


But I thought the magnification was +0.667?
 


alicia113 said:
Is there an equation for focal length.?

Yes, the lens equation.
 


Is it

1/Di=1/f - 1/do
 
Last edited:
  • #10
alicia113 said:
Is it

1/Di=1/f - 1/do

But for that I am not sure where the numbers fit in. I do not have focal length. All I have is magnification and where the object is located
 
  • #11
alicia113 said:
But for that I am not sure where the numbers fit in. I do not have focal length. All I have is magnification and where the object is located


I have 1/Di = 1/f - 1/3.5cm


I am missing the focal length


Wait that's the thin lens equation wow ok hold on.
 
  • #12


No I need the thin lens equation .. I am so confused right now !
 
  • #13
  • #14


Ok so I have my focal length as +4.3 magnification as 5.24 and distance of image is -18.3
 
  • #15


How do I find position of image
 

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