Question

in concave lens
is vist
is placed at infini
ad at F, wl​

Answer 1

Answer:

Explanation:

Given,

Object distance, u=10 cm

Real image ⇒ other ride ⇒v=+ve

Magnification, m+3⇒−  

u

v

​

=3

So, v=−3u=−3×(−10)=30 cm

Combined focal constant =F

then  

f

1

​

=  

v

1

​

−  

u

1

​

=  

30

1

​

−  

−10

1

​

=  

30

1+3

​

=  

30

4

​

 

⇒F=  

2

15

​

 cm

but  

F

1

​

=  

f  

1

​

 

1

​

+  

f  

2

​

 

1

​

 so  

15

2

​

=  

−30

1

​

+  

f  

2

​

 

1

​

 

Because concave f  

1

​

=−30 cm on solving we get  

30

4

​

+  

30

1

​

=  

f  

2

​

 

1

​

 

⇒f  

2

​

=6 cm +ve⇒ convex.