Question

If an object is kept distance of 15cm and its focal length=7.5 find the distance of image​

Answer 1

Answer:

Explanation:

For the lens ,

u=−15 ;f=+10

v

1

​  

−  

u

1

​  

=  

f

1

​  

 

v

1

​  

−  

15

−1

​  

=  

10

1

​  

 

v=+30

Distance between mirror and lens is 10 cm then the image is formed at 20cm from the mirror , this becomes object distance for the mirror and the image formed by the mirror serves as the object for lens.

Final image formed by lens is same at the initial position as that of the object

for lens,

v=+15 ; f=+10

v

1

​  

−  

u

1

​  

=  

f

1

​  

 

15

1

​  

−  

u

1

​  

=  

10

1

​  

 

u=−30 ,   this is the image for the mirror

now for mirror , u=+20 ;v=+20

v

1

​  

+  

u

1

​  

=  

f

1

​  

 

20

1

​  

+  

20

1

​  

=  

f

1

​  

 

f=10 cm, hence option B is correct

Answer 2

Answer:

15 ×7.5

Explanation:

u will get the amswer