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20 Physics -- Reflection at Plane Surfaces

Minimum height of plane mirror required to observe image of a man of height 6ft is 3ft when man's 1 m apart from the mirror . Is the size of image affected when distance between man and mirror is increased to 3 m  ? Explain. 

Minimum height of plane mirror required to observe image of a man of height 6ft is 3ft when man's 1 m apart from the mirror . Is the size of image affected when distance between man and mirror is increased to 3 m  ? Explain. 

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In order to see full image of a person, the minimum size of the mirror should be one half the person’s height. This is so because, in reflection, the angle of incidence is equal to angle of reflection. So, to see the image of a 6 ft tall person, a 3 ft long mirror is required.

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BAD=x , ABD=yHere AD and BD are Normal lines,

OBA=90y OAB=90xΔOAB;
θ+90y+90x=180 x+y=θTotal deviation is2(90x)+2(90y) =3602(x+y) =3602θ
Here from the question deviation angle is 300olet, a be the angle between two plane mirror, therefore, 300o = 360o - 2a so, a= 30o

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