Calculating Objective Lens Focal Length for Compound Microscope

[thundercats]

Homework Statement

The barrel of a compound microscope is 14.8 cm in length. The specimen will be mounted 1.03 cm from the objective, and the eyepiece has a 4.92 cm focal length. Determine the focal length of the objective lens

Homework Equations

(1/Do)+(1/Di)= (1/f)

The Attempt at a Solution

what did was i added 1.03 with 13.8 to get the distance of object from the eye piece. then i plugged the numbers in the equation ( with the focal point of the eye piece) to get the distance of the image from the eyepiece. then i used the image distance i got and subtracted it from the 14.8 to get the image distance from the objective lense to the image and i plugged into solve for f. but my answer comes down to be .99 cm which is wrong

 

[tiny-tim]

… what did was i added 1.03 with 13.8 to get the distance of object from the eye piece. then i plugged the numbers in the equation ( with the focal point of the eye piece) to get the distance of the image from the eyepiece. then i used the image distance i got and subtracted it from the 14.8 to get the image distance from the objective lense to the image and i plugged into solve for f. but my answer comes down to be .99 cm which is wrong

Hi thundercats!

I can't really tell what you did without seeing your equations …

but you don't seem to have used the position of the intermediate image.

 

[thundercats]

i think i see what you are saying but now I am more confused. this is how i have started to set it up again. what i don't seem to understand is how to use the 14.8 which is the length of the barrel. I am not sure if I am suppose to use it to find Df (distance of final image)or something
(1/1.03)+(1/Di1)=(1/F1)
(1/Di1)+(1/Df)=(1/4.92)

 

[tiny-tim]

… what i don't seem to understand is how to use the 14.8 which is the length of the barrel.

14.8 is the sum of two of the distances.

 

[thundercats]

hmm. by saying its the sum of the two distances I am assuming ur saying that its the distance between the two lenses of the compund microscope so i guess i can plug that into my 2nd equation making it look like this
(1/Di1)+(1/14.8-Di1)=(1/4.92)
am i close :D. by the way how do u know to reply back to my posts i was just wondering :D

 

[thundercats]

there is still something wrong with it i can't figure out what i was thinking maybe the sign has to be negetive since the final image is going to be to the left of the second lens meaning
(1/Di1)-(1/14.8-Di)=(1/4.92)

 

[tiny-tim]

Just got up … :zzz:

hmm. by saying its the sum of the two distances I am assuming ur saying that its the distance between the two lenses of the compund microscope so i guess i can plug that into my 2nd equation making it look like this
(1/Di1)+(1/14.8-Di1)=(1/4.92)
am i close :D. by the way how do u know to reply back to my posts i was just wondering :D

That's right.

It should work … show us what you got.

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[thundercats]

ur da man thnx for ur help