Question

tyre size of the image of an object placed at infinity formed by a convex lens of the focal length 30 cm is 20 CM if a concave lens of the focal length 20 cm is placed between the convex lens and the image at the distance of 26m from the convex lens then your size of the image will be

a 2.5cm

b 1.25cm

c 1.50cm

d 20vm​

Answer 1

Answer:

Explanation:

We get the image distance due to the lens using lens formula,

v

1

​  

−  

u

1

​  

=  

f

1

​  

 

or

v

1

​  

=  

15

1

​  

−  

30

1

​  

 

or

v=30cm in front of the convex mirror, which means 20cm behind the mirror. Assuming mirror to reflect from both the sides and this image will act as virtual object for mirror and second image, I  

2

​  

 will be formed at 20 cm in front of mirror. That is 10 cm in front of lens.

Understanding the convention used while taking +ve and -ve sign for image and object distance, the direction along which ray of light travels is taken as +ve.

So, here, the ray of light is coming from behind the mirror towards lens, for the second image, I  

2

​  

 with respect to lens,  

u=+10cm;f=15cm

So, applying lens formula,

v

1

​  

−  

u

1

​  

=  

f

1

​  

 

or

v

1

​  

−  

10

1

​  

=  

15

1

​  

 

or

v=6cm from lens (in front of lens)

So this image is at a distance of 16 (10 + 6) cm in front of mirror.