A lens of focal length 10 cm is being used by a student in the laboratory as magnifying glass. His near point distance is 25 cm. What magnification is the student getting ?

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Solution

f= 10cm(Since its a convex lens)

v= -25cm (Image distace for eyes)

u=? (Object distance)

m=? (magnification)

Using lens formula,

1/v - 1/u=1/f

=> 1/v-1/f=1/u

=> -1/25-1/10=1/u

=> -2-5/50=1/u

=> -7/50=1/u

=> -50/7=u

Now, Magnification m=v/u

=>m= 25/-50/7

=> m=25*7/-50

=> m= -7/2

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A lens of focal length 10 cm is being used by a student in the laboratory as magnifying glass. His near point distance is 25 cm. What magnification is the student getting ?

f= 10cm(Since its a convex lens) v= -25cm (Image distace for eyes) u=? (Object distance) m=? (magnification) Using lens formula, 1/v - 1/u=1/f => 1/v-1/f=1/u => -1/25-1/10=1/u => -2-5/50=1/u => -7/50=1/u => -50/7=u Now, Magnification m=v/u =>m= 25/-50/7 => m=25*7/-50 => m= -7/2

f= 10cm(Since its a convex lens)

v= -25cm (Image distace for eyes)

u=? (Object distance)

m=? (magnification)

Using lens formula,

1/v - 1/u=1/f

=> 1/v-1/f=1/u

=> -1/25-1/10=1/u

=> -2-5/50=1/u

=> -7/50=1/u

=> -50/7=u

Now, Magnification m=v/u

=>m= 25/-50/7

=> m=25*7/-50

=> m= -7/2