Question

a small mirror of area A and mass m is suspended in a vertical plane by a weightless string a beam of light on intensity i fall normally on the mirror and the string is deflected from the vertical by very small angle force on mirror is​

Answer 1

a small mirror of area A and mass m is suspended in a vertical plane by a weightless string a beam of light on intensity i fall normally on the mirror and the string is deflected from the vertical by very small angle force on mirror is

Explanation:

Force on the mirror due to incident light beam is

2Ia/c

​

.

Balancing the torque about the hinge, assuming length of string be L we get,

2Ia/c

​

lcos(θ)=mglsin(θ),

So tan(θ)=

2Ia/cmg

​

.

Then due to deflection the mirror about hinge due to light is very small, we can approximate tan(θ) by θ.

Thus the angle θ=

2Ia/cmg

​

.

Answer 2

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