Question

How far should an object be placed from a convex lens of focal lenght 20 cm to obtain its real image at a distance of 30 cm from the lens​

Answer 1

Answer:

In convex lens

Focal length ,f=20 cm

Image distance,v=30 cm

Height of object,h=6 cm

To find:

Object distance from convex lens and height of the image.

Solution:

We know that lens formula

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

f

1

=

v

1

−

u

1

Using the formula

\frac{1}{20}=\frac{1}{30}-\frac{1}{u}

20

1

=

30

1

−

u

1

\frac{1}{u}=\frac{1}{30}-\frac{1}{20}

u

1

=

30

1

−

20

1

\frac{1}{u}=\frac{2-3}{60}

u

1

=

60

2−3

\frac{1}{u}=-\frac{1}{60}

u

1

=−

60

1

u=-60 cmu=−60cm

An object should be placed at distance 60 cm from the convex lens.

We know that

\frac{h'}{h}=\frac{v}{u}

h

h

′

=

u

v

\frac{h'}{6}=\frac{30}{-60}=-\frac{1}{2}

6

h

′

=

−60

30

=−

2

1

h'=6\times -\frac{1}{2}=-3 cmh

′

=6×−

2

1

=−3cm

Height of image=3 cm

Answer 2

Answer:

your answer is 3cm.

Explanation:

Answer by @MrMysteryy❤️