Question

A girl stands in front of mirror at a distance of 1m.She sees her image whose height is 1/5th of real height,Find nature and focal length

Answer 1

Answer:

Explanation:

His distance from the mirror is the  

object distance, treating him as an object, So,

Applying mirror formula

u

1

​  

+  

v

1

​  

=  

f

1

​  

 

Here, u is negative and f for convex  

mirror is positive , So,

−f

1

​  

+  

v

1

​  

=  

f

1

​  

 

v

1

​  

=  

f

2

​  

 

Also, m(magnification) =  

u

−v

​  

 

m=  

⎣

⎢

⎢

⎢

⎡

​  

 

−(  

f

1

​  

)

−  

f

2

​  

 

​  

 

⎦

⎥

⎥

⎥

⎤

​  

 

−1

=  

2

1

​  

 

We know,

m=  

objectlength

imagelength

​  

 

Here, object length = Boy's height = 1 m.

So,

m=  

1m

imagelength

​  

=  

2

1

​  

 

⇒ image length =  

2

1

​  

=0.5m