A thin convex lens from a real Image of a certain object 'p' times it size .The size of real image become 'q' times that of object when the lens is moved nearer to the object by a distance 'a' find focal length of the lens?

Options

A. ` (|a|)/(| p - q | ) `
B. ` ( apq ) / ( | q - p | ) `
C. Both 1 & 2
D. None

Answer

C

Explanation

` f = (x ) /( m _ 1 - m _ 2 ) = (a ) / ( p - q ) `
and also ` f= (apq ) /( p- q ) " " ( because pq = 1 ) `