Question

Why is it beneficial to perform focal point of a convex lens exercises in a dimly-lit room?
What is the focal length of a convex lens that produces an image on a screen 40 cm away with an object placed 10 cm from the lens? What is the magnification? Is the image inverted or upright? Show all calculations in your answer.

Answer 1

Explanation:

It is given that,

The object distance from the lens is 10 cm, u = -10 cm

Image is formed at a distance of 40 cm away from the lens, u = 40 cm

The lens formula is : $\dfrac{1}{v}-\dfrac{1}{u}=\dfrac{1}{f}$, v is image distance

$\dfrac{1}{40}-\dfrac{1}{-10}=\dfrac{1}{f}\\\\f=8\ cm$

The focal length is 8 cm

Magnification,

$m=\dfrac{v}{u}\\\\m=\dfrac{40}{-10}\\\\m=-4$

The magnification is negative, it means that the formed image is inverted.