Question

A convex lens forms a real image magnified four times, when the object is placed at a distance of 6 cm from the lens. Calculate the focal length of the lens.​

Answer 1

${\bold{\huge{\underline{\orange{\underline{\ANSWER:-}}}}}}$

$\huge\pink{\underline{Given}}$

• m (magnification) = 4
• u (object distance) = -6cm

FORMULA:-

• m (magnification) = -v/u

[where “v = image distance”]

• 1/v - 1/u = 1/f [f = focal length]

SOLUTION:-

m = -v/u

=> 4 = -v/(-6)

=> v = 24cm

Form lens formula;

1/v - 1/u = 1/f

=> 1/(24) - 1/(-6) = 1/f

=> 1/f = 1/24 + 1/6

=> 1/f = 5/24

=> f = 24/5

=> f = 4.8cm .

• Hence the focal length of the lens is “4.8cm” .

$\bigstar\:\underline{\boxed{\bf{\red{Required Answer}:4.8cm}}}$