An illuminated object lies at a distance 1.0 m from a screen. A convex lens is used to form the image of object on a screen placed at distance 75 cm from the lens. Find : (i) the focal length of lens, and (ii) the magnification.

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Solution

Image Distance ,(v)= 75 cm (right hand side)

Object distance, (u)= -1m = 100cm ( In convex lens object is in the left hand side)

Focal length, (f)= ??

Lens Formula

1/f=1/v−1/u

=1/75cm−1/(−100)

=1/300cm

f= 300 cm

f= 300/100

f=3m

Magnification, m=v/ u

=75/100

m =0.75

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Q. An illuminated object lies at a distance 1.0 m from a screen. A convex lens is used to form the image of the object on a screen placed at a distance 75 cm from the lens. Find :
1) the focal length of lens
2) the magnification.

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An illuminated object lies at a distance 1.0 m from a screen. A convex lens is used to form the image of object on a screen placed at distance 75 cm from the lens. Find : (i) the focal length of lens, and (ii) the magnification.

Image Distance ,(v)= 75 cm (right hand side) Object distance, (u)= -1m = 100cm ( In convex lens object is in the left hand side) Focal length, (f)= ?? Lens Formula 1/f=1/v−1/u =1/75cm−1/(−100) =1/300cm f= 300 cm f= 300/100 f=3m Magnification, m=v/ u =75/100 m =0.75

Image Distance ,(v)= 75 cm (right hand side)

Object distance, (u)= -1m = 100cm ( In convex lens object is in the left hand side)

Focal length, (f)= ??

Lens Formula

1/f=1/v−1/u

=1/75cm−1/(−100)

=1/300cm

f= 300 cm

f= 300/100

f=3m

Magnification, m=v/ u

=75/100

m =0.75