Question

Convex lens of focal length 15cm when the object is placed at a distance of 25 cm from the lens. Determine the size of the image formed if the size of the object is 4cm. ​

Answer 1

Answer:

Explanation:

F= +15cm

u= + 25cm

v= ?

Height of object= 4cm

height of image=?

using lens formula-

$\frac{1}{f} =\frac{1}{v} -\frac{1}{u}$

1/15= 1/v   -1/25

1/15 + 1/25 =  1/v

6/75= 1/v

therefore v= 75/6

to find size of image we use magnification formula

$m= -\frac{v}{u }$

m= $\frac{Height of image }{Height of object }$

we have -

m=  - v/u  = height of image/ height of object

m=  - 76/6  / 25 = height of image/ 4

m= $-\frac{75}{150} = \frac{height of image }{4}$

by cross multiplication

m= -75 X 4 =  150(H img)

m= $\frac{- 75 X 4}{150 }$= height of image

m= - 20 cm

m(-ve) = Real and inverted image

m greter than 1 ⇒ magnified

I hope this helps