Question

An object of 5.0 cm size is placed at a distance of 20.0 cm from a converging mirror of focal length 15.0 cm. At what distance from the mirror should a screen be placed to get the sharp image? Also calculate the size of the image.

Answer 1

Concave mirror is a converging mirror.
Distance of the object from the mirror 'u' = -20 cm

Height of the object 'h_o' = 5 cm

Focal length of the mirror 'f' = -15 cm

We have to find the distance of the image 'v' and the height of the image 'h_i'.

Using the mirror formula, we get 

`1/f=1/v+1/u` 

`1/-15=1/v+1/-20=1/v-1/20` 

or` 1/v=1/20-1/15` 

`or 1/v=(3-4)/60=1/60` 

`or v=-60` cm 

Thus, the image is at a distance of 60 cm in front of the mirror.  

Now, using the magnification formula, we 

 get 

`m=-v/u=h_i/h_o`  

or `h_i/5=-(-60)/-20`  

or h_i/5=-3 

or `h_i =-3xx5=-15` cm 

Therefore, the height of the image will be 15 cm, and the negative sign shows that the image will be formed below the principal axis.