Calculating Focal Length and Image Height of a Lens

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Homework Help Overview

The problem involves a lens forming an image of an object, with specific distances provided for both the object and the image. The context includes determining the focal length of the lens and the characteristics of the image, such as its height and orientation.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants discuss the application of the lens formula and the characteristics of the image formed by the lens. There are attempts to calculate the focal length and image height, along with questions about the nature of the image (real or virtual) and the correctness of the calculations.

Discussion Status

Some participants have provided guidance regarding the sign conventions in the lens formula, particularly concerning virtual images. There is an ongoing exploration of the calculations and interpretations of the results, with differing opinions on the focal length and image characteristics.

Contextual Notes

Participants are navigating the implications of the sign conventions in the lens formula, particularly in relation to virtual images and the characteristics of diverging lenses. There is also mention of a principle-ray diagram, which is part of the problem context but not fully explored in the discussion.

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Homework Statement



A lens forms an image of an object. The object is 16 cm from the lens. The image is 12 cm
from the lens on the same side as the object. (a) What is the focal length of the lens? Is the
lens converging or diverging? (b) If the object is 8.5 mm tall, how tall is the image? Is it erect or inverted? Draw a principle-ray diagram.

Homework Equations



1/f = 1/s + 1/s'

The Attempt at a Solution



I got 6.8cm for the focal length and .638cm for the height. When I draw my principle-ray diagram, the object and image are to the left of the second focal point, which is to the left of the lens. Shouldn't the 2nd focal point be between the object and image on the left side of the lens?
 
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Anybody?
 
The image is at the same side as the object. Is the image real or virtual?

ehild
 
virtual
 
Your result for the focal length is not correct. The virtual image distance has minus sign in the lens formula. Calculate again.

ehild
 
-48cm?
 
Yes, the focal length is -48 cm. The lens is diverging so the focal length is negative.

ehild
 

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