CBSE Class 12-science Answered
In the following question, why do we use the formula l/fo(D/fe) and not L/fo(1+D/fe)?
The total magnification produced by a compound microscope is 20.The magnification produced by the eyepiece is 5.The microscope is focussed on a certain object.The distance between the objective and eyepiece is observed to be 14cm.If the least distance of distinct vision is 20cm calculate the focal length of the objective and the eyepiece.
Asked by Hppothen | 21 Feb, 2020, 02:41: PM
Expert Answer
In Compound microscope, magnification me of eye piece when image is formed at near point is given by
me = 1 + ( D/fe ) .........................(1)
where D is the near point distance, fe is focal length of eye piece.
when image is formed at infinity, magnification me is given by , me = D/fe ...................(2)
When image is formed at infinity, it is comfortable to view and it gives less strain to the eye.
Hence for compound microscope , image is formed at infinity most of the times .
Hence we need to use the formula given in eqn.(2) for eye piece magnification.
----------------------------------------------
Total magnification = mo me = 20
magnification of eyepiece = me= 5
Hence magnification of objective = mo = 4
magnification of eyepiece = me = D/fe = 20/fe = 5 , hence eyepiece focal length fe = 20/5 = 4 cm
magnification of objective = mo = L/fo = 4 , i.e. tube length L = 4fo
Distance between objective and eyepiece = fo + L + fe = 14 cm (given)
By substituting for L and fe in above expression, we get, fo + 4fo + 4 = 14 , i.e., 5 fo = 10
Hence focal length of objective, fo = 2 cm
Answered by Thiyagarajan K | 21 Feb, 2020, 09:42: PM
Concept Videos
-
Electric Charge - Part 1
This video describes the concept of charge, conductors and insulators, and ... -
Gold Leaf Electroscope - Part 1
This video explains the basic properties of electric charges. -
Coulom's Law of Electric Force - Part 1 ...
This video describes Coulomb's law to calculate the force between any two p... -
All about electric fields
Define electric field in terms of Coulomb's force. Apply superposition prin... -
Electric Field Lines
This video explains the representation of electric field due to a single ch...
CBSE 12-science - Physics
Asked by aishaisha091098 | 19 Apr, 2024, 04:54: PM
ANSWERED BY EXPERT
CBSE 12-science - Physics
Asked by dasrituparna1999 | 13 Apr, 2024, 06:56: AM
ANSWERED BY EXPERTCBSE 12-science - Physics
Asked by dasrituparna1999 | 12 Apr, 2024, 09:26: PM
ANSWERED BY EXPERTCBSE 12-science - Physics
Asked by mishrigupta19319 | 08 Apr, 2024, 06:28: PM
ANSWERED BY EXPERTCBSE 12-science - Physics
Asked by madhav9119887644 | 07 Apr, 2024, 08:10: PM
ANSWERED BY EXPERTCBSE 12-science - Physics
Asked by mishrigupta19319 | 07 Apr, 2024, 11:23: AM
ANSWERED BY EXPERTCBSE 12-science - Physics
Asked by adityagalar2007 | 06 Apr, 2024, 01:06: PM
ANSWERED BY EXPERTCBSE 12-science - Physics
Asked by amlanmcob | 06 Apr, 2024, 12:27: PM
ANSWERED BY EXPERTCBSE 12-science - Physics
Asked by hussain221man | 05 Apr, 2024, 08:44: PM
ANSWERED BY EXPERT
