Question

A bioconvex lens has a radius Oscar vector of magnitude 20cm. which one of the following options describe best the image formed at an object of height 2cm placed from 30 from the lens?
a) virtual, upright, height =0.5 b) real,inverted, height = 4
c) real,inverted, height = 1cm
d) virtual,upright,height = 1cm​

Answer 1

Q]_____?

=> Option B

Explanation:

Given, R = 20cm

ho = 2cm and u = -30cm

In general we have assumed = 1.5

As 1/f = ( 1.5 - 1 ) × 2/20 = 1/20

So, f = 20cm

1 / f = 1 / v + 1 / u

1 / 20 = 1 / v + 1 / 30

1 / 20 = 1 / v + 1 / 30

1 / v = 1 / 20 - ( 1 / 30 )

1 / v = 10 / 600

∴ v = 60 cm

As,

m = v/u = 60/ (-30) = -2

m = hi / ho = -2

hi = - 2 × 2

∴ hi = - 4cm

Here, Image is real, inverted, magnified and height of the image is 4cm !

_____________________________________

Answer 2

Given, R = 20cm

ho 2cm and u = -30cm

In general we have assumed = 1.5

As 1/f = (1.5 - 1) × 2/20 = 1/20

So, f = 20cm

1/f = 1/v+1/u

1/20=1/v + 1/30

1/20 = 1/v + 1/30 1/v=1/20 - (1/30)

1/v = 10/600

:. v = 60 cm

As,

m = v/u = 60/(-30) = = -2

m = hi/ho= -2

hi = - 2 x 2

.. hi = - 4cm

Here, Image is real, inverted, magnified and height of the image is 4cm!