The power of a lens is +4D. Find the focal length of this lens. An object is placed at a distance of 50 cm…
The power of a lens is +4D. Find the focal length of this lens. An object is placed at a distance of 50 cm from the optical centre of this lens. State the nature and magnification of the image formed by the lens and also draw a ray diagram to justify your answer.
Solution
Focal length of lens, f(m) = $\dfrac{1}{P}$
P = +4.0 D
⇒ f = 1/+4D = 0.25 m = 25 cm
Real and inverted
Magnification = -1
[Deduct ½ mark if direction of rays is not marked]