Answer 1

A concave mirror is a converging mirror.

Distance of the object from the mirror 'u' = -20 cm

Height of the object 'h_o' = 1 cm

Height of the image 'h_i' = -4 cm
We have to find the distance of the image 'v' and focal length of the mirror 'f'.

Using the magnification formula, we get  

`m=h_i/h_o=-v/u` 

`-4/1=-v/-20` 

`v=20xx-4/1=-80` cm 

Thus, the distance of the image 'v' is 80 cm.

Now, using the mirror formula, we get 

`1/f=1/v+1/u` 

`1/f=1/-80+1/-20=-1/80-4/80=-5/80`  

`1/f=-1/16` 

f=-16 cm 

Thus, the focal length of the concave mirror is 16 cm.