Question 202: Ray Optics

Question

Two lenses of power $$-15$$ $$D$$ and $$+5$$ $$D$$ are in contact with each other. The focal length of the combination is

Accepted Answer

Power of combination is given by
$$P = {P_1} + {P_2} = \left( { - 15 + 5} ight)D$$  $$\,\,\,\,\,\,\,\,\, =  - 10D.$$
Now, $$P = {1 \over f} \Rightarrow f = {1 \over P} = {1 \over { - 10}}$$ metre
$$	herefore$$ $$f =  - \left( {{1 \over {10}} 	imes 100} ight)cm =  - 10\,cm.$$

Answer

$$ + 10\,cm$$

Answer

$$ - 20\,cm$$

Answer

$$ - 10\,cm$$

Answer

$$ + 20\,cm$$

Ray Optics

Two lenses of power $-15 D and +5 D$ are in contact with each other. The focal length of the combination is

Choose the correct answer: