Question

Two thin lenses are in contact and the focal length of the combination is $80\, cm$. If the focal length of one lens is $20 \,cm$, then the power of the other lens will be

• A. $1.66\, D$
• B. $4.00\, D$
• C. $-100\, D$
• D. $-3.75\, D$

Answer 1

Answer: (D)

$-3.75\, D$

Answer 2

$P_{2}=P-P_{1}=\frac{100}{80}-\frac{100}{20}=-3.75\quad D$