Question

A ray reflected successively from 2 plane mirrors inclined at certain angle undergoes a deviation of 300 degree. Then what is the number of images observable?

Answer 1

the angle of deviation depend only angle between mirrors
see
let angle of incidence at first mirror be α 
and it is incident at second mirror be β
look at the diagram
Now let the angle between mirrors be Ф
so Ф+90-α+90-β=180
then α+β=Ф
and for another triangle
2α+2β+60=180
Ф+30=90
Ф=60
so the no. the images formed is (360/Ф)-1
6-1=5
so 5 images will be formed