How does the presence of water affect the image formed by a converging lens?

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Homework Help Overview

The discussion revolves around the effects of water on the image formed by a converging lens, specifically in the context of a needle placed in a beaker. The problem involves understanding the changes in image distance and object distance when water is introduced into the setup.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants explore the impact of water's refractive index on the apparent position of the needle and question how to apply the lens maker's formula in this context. There is also discussion about the apparent depth of the needle when viewed through the water.

Discussion Status

Participants are actively engaging with the problem, with some providing calculations for apparent depth and others questioning the accuracy of those values. There is a mix of interpretations regarding the depth and the application of the lens formula, indicating a productive exploration of the topic.

Contextual Notes

There is confusion regarding the inclusion of air in the calculations and the correct interpretation of real versus apparent depth. The problem is framed within the constraints of a homework assignment, which may limit the information available for discussion.

apunisheriii

Homework Statement


A needle of length 5.0cm placed at the bottom of a beaker and a converging lens of focal length 20.0cm is held 30.0cm from the needle.The needle is illuminated with a lamp from the bottom.An image of the needle is formed on a screen.The beaker is now filled with water(refractive index=4/3)to a depth of 20cm.What change can be observed in the image?
If the screen is moved to get a new sharp image,what will the image distance and object be in this new position??

i squeezed my brain so hard..still don hv any idea at all..becoz there's a space (air)between the lens and the water.When i am using the lens maker's formula,im confusing whether i should assume there r three lens -water,converging lens and water or two or one..
can somebody give some hints about how to solve it??
 
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Forget about the lens for a moment. From the viewpoint of someone looking down into the beaker (from the position of the lens), will the addition of the water make the apparent position of the needle closer or farther away? By how much?
 
oh!
the apparent depth is 22.5cm from the lens
and let u=22.5cm and solve it by lens formula
is it correct??
 
sorry...
mistake...real depth shouldn't include the air...u=25cm
by the way!thnx!
 
apunisheriii said:
the apparent depth is 22.5cm from the lens
How did you get that value? Realize that the water is only 20 cm deep.
 
apunisheriii said:
sorry...
mistake...real depth shouldn't include the air...u=25cm
by the way!thnx!
Now you've got it. :smile:
 

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