Question for the Day 26-9-2007

1. A biconvex lens of focal length f forms a circular image of sun of radius r in focal plane. Then
(A) πr^2 ∝ f
(B) πr^2 ∝ f^2
(C) if lower half part is covered by black sheet, then area of the image is equal to πr^2/2
(D) if f is doubled, intensity will increase

2.MgSO-4 on reaction with NH-4OH and Na-2HPO-4 forms a white crystalline precipitate. What is its formula?

(A) Mg(NH-4)PO-4
(B) Mg-3(PO-4)-2
(C) MgCl-2.MgSO-4
(D) MgSO-4


3. For x > 0, Lim[(Sin)^(1/x)+(1/x)^sinx)] is
(x -> 0)
(A) 0
(B) -1
(C) 1
(D) 2