You have a choice between two lenses of focal lengths fa and fb, where fb = 2fa, to use as the objective lens in building a compound microscope. If the magnification you obtain using lens a is
Ma, what will be the magnification when using lens b?
A) $M b = M _ { a } / 4$
B) $M _ { b } = M _ { a } / 2$
C) $M _ { b } = 8 M _ { a }$
D) $M _ { b } = 4 M _ { a }$
E) $M _ { b } = 2 M _ { a }$

Question

You have a choice between two lenses of focal lengths fa and fb, where fb = 2fa, to use as the objective lens in building a compound microscope. If the magnification you obtain using lens a is
Ma, what will be the magnification when using lens b? 
A) $M b = M _ { a } / 4$
B) $M _ { b } = M _ { a } / 2$
C) $M _ { b } = 8 M _ { a }$
D) $M _ { b } = 4 M _ { a }$
E) $M _ { b } = 2 M _ { a }$

Quizplus · Accepted Answer

The magnification of a compound microscope is inversely proportional to the focal length of the objective lens. Since $f_b = 2f_a$, the magnification with lens b will be half that with lens a, so $M_b = M_a / 2$.

You Have a Choice Between Two Lenses of Focal Lengths Mb=Ma/4M b = M _ { a } / 4Mb=Ma​/4

You Have a Choice Between Two Lenses of Focal Lengths $M b = M _ { a } / 4$