Question

What is the value of α for which there are maximum 2 reflections only ?

Answer 1

<CAB= α (Based on i=r)

<BCA= 120-α (Angle Sum Property)

<DCE=120-α (Based on i=r)

The final ray must be above the horizontal. So the angle of the ray with the mirror must be lower than 60 degree. 

Therefore, 

120-α>60

α>60

(D) 65

I am answering my own question as I have the appropriate knowledge about this specific topic now and this question might be helpful to other students in the future.

Answer 2

Correct option is (D) 65°

For 2 reflection

Reflection at M₂ should be greater than 30°

\(\alpha\) > 30°

from horizontal 

\(\alpha\) = 90° - 30°

\(\alpha\) = 60°

So,

\(\alpha\) > 60°

Comments

The solution doesn't even answer the question properly. Looks like you copied it from somewhere. The final ray must be above the horizontal. So the angle of the ray with the mirror must be lower than 60 degree.

The angle opposite to 60 degree is α, therefore the other angle between mirror and incident ray is 120-α based on ASP. The angle of the reflected with the mirror is 120-α too.

Therefore,
120-α<60
Solve the inequality to get α>60. Option D is the right answer.

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