[tex]\huge\star\underline{\mathtt\red{A}\mathtt\green{N}\mathtt\blue{S}\mathtt\purple{W}\mathtt\orange{E}\mathtt\pink{R}}\star\:[/tex]
The magnifying power of a simple microscope is defined as the ratio of the angle subtended at eye by the image to the angle subtended at unaided eye by the object kept at distance of distinct image (DDV).
M.P. =angle subtended at eye by the imageAngle subtended at unaided eye by the object at DDVM.P. =βα−−−−(1)
Where β is the angle subtended at the eye by the imageA′B′
andαis the angle subtended at the eye by the object kept at DDV.
Consider △A ′ B ′ O,tanβ=A′B′OB′=ABusinceβ is very small-tanβ≈ β=ABu
tanα=ABDsinceα is very small-tanα≈α=ABD
Put value in equation (1), we get
M.P.=ABuABD=Du
From lens formula we have: 1v−1u=1f
According to sign convention. Here u and v are negative and fis positive,
Therefore we get-
1u=1v+1fDu=Dv+DfM.P.=Dv+Df
This equation gives the magnifying power of a simple microscope.
Case (i): If the image is formed at distance of distinct vision i.e. DDV i.ev=D
, then
M.P.=DD+Df=(1+Df)
Hence magnifying power is (1+Df), if the image formed at distance of distinct vision.
Case (ii): If the image is formed at infinity i.e. v=∞;then
M.P.=D∞+Df=(Df)
Hence magnifying power is Df, if the image formed at infinity.