Question

Two lenses whose powers are $4D$ and $-2D$ are kept in contact. The power of the compound lens is:

• A. $6D$
• B. $2D$
• C. $-2D$
• D. $4D$

Answer 1

The correct option is B $2D$

Here,

$P_1=4D$

$P_2=-2D$

Total power of the compound lens is given by,

$P_T=P_1+P_2=4D+(-2D)=2D$

$\therefore$ power of the compound lens $=2D$