On an optical bench of 150 cm, a student used a concave mirror of focal length 20 cm to observe object distance (u) and image distance (v) respectively as:

(A) (40 cm, 10 cm)
(B) (60 cm, 15 cm)
(C) (80 cm, 38 cm)
(D) (60 cm, 30 cm)
(E) (40 cm, 40 cm)

Choose the correct answer from the options given below:

(D) and (E) only

The correct answer is Option (4) → (D) and (E) only

To check which of the given object (u) and image (v) distances correspond to the concave mirror of focal length (f) = 20 cm

$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$ [lens formula]

(D) $u=60cm,v=30cm$

$\frac{1}{f}=\frac{1}{30}+\frac{1}{60}$

$\frac{1}{f}=\frac{60}{3}=20cm$

(E) $u=40cm,v=40cm$

$\frac{1}{f}=\frac{2}{40}=20cm$