Aditi Chauhan
Last Activity: 10 Years ago
Sol. The lady can not see objects closer than 40 cm from the left eye and 100 cm from the right eye.
For the left glass lens,
v = – 40 cm, u = – 25 cm
∵ 1/f = 1/v – 1/u = 1/-40 – 1/-25 = 1/25 – 1/40 = 3/200 ⇒ f = 200/3 cm
For the right glass lens,
V = - 100 cm, u = - 25 cm
1/f = 1/v – 1/u = 1/-100- 1/-25 = 1/25 – 1/100 = 3/100 ⇒ f = 100/3 cm
(a) For an astronomical telescope, the eye piece lens should have smaller focal length. So, she should
use the right lens (f = 100/3 cm) as the eye piece lens.
(b) With relaxed eye, (normal adjustment)
F base 0 = 200/3 cm, f base e = 100/3 cm
Magnification = m = f base 0/f base e = (200/3)/(100/3) = 2