JEE PYQ: Ray Optics Question 53
Question 53 - 2019 (12 Jan Shift 2)
What is the position and nature of image formed by lens combination shown in figure? ($f_1$, $f_2$ are focal lengths)
$f_1 = +5$ cm, $f_2 = -5$ cm, object at 20 cm from lens A, separation between lenses = 2 cm.
(1) 70 cm from point B at left; virtual
(2) 40 cm from point B at right; real
(3) $\frac{20}{3}$ cm from point B at right, real
(4) 70 cm from point B at right; real
Show Answer
Answer: (4)
Solution
By lens’s formula, $\frac{1}{V} - \frac{1}{u} = \frac{1}{f}$ For first lens, ($u_1 = -20$) $\frac{1}{V_1} - \frac{1}{-20} = \frac{1}{5} \Rightarrow V_1 = \frac{20}{3}$ Image formed by first lens will behave as an object for second lens so, $u_2 = \frac{20}{3} - 2 = \frac{14}{3}$ $\frac{1}{V_2} - \frac{1}{\frac{14}{3}} = \frac{1}{-5} \Rightarrow V_2 = 70$ cm
BETA
