optics again

for 1..tan i_p=n....
now i_p +r=90 (given)....hence polarisation occurs

n=√3 i_p=60°(ANS)

for this particular ang. da reflected lite is plane polarised with vibrations _|_ to incident plane(BREWSTERS LAW)

2) v+u is a Constant.

(Assuming Lens is in b/w obj. n img.)

Fr position I => v₁+30 =D
Fr position II=> v₂+50=D

Also f = 30*v₁/(30+v₁) = 50*v₂/(50+v₂)

Writng v₁, v₂ in terms of D, & solving the 2 equations shud give the answer...