IIT-JEE 2009 · Paper 1 · Physics Q50

← IIT-JEE 2009 · Paper 1

PhysicsMultiple correct+4 / -1Question 50 of 60

A student performed the experiment of determination of focal length of a concave mirror by u-v method using an optical bench of length 1.5 meter. The focal length of the mirror used is 24 cm. The maximum error in the location of the image can be 0.2 cm. The 5 sets of (u, v) values recorded by the student (in cm) are: (42, 56), (48, 48), (60, 40), (66, 33), (78, 39). The data set(s) that cannot come from experiment and is (are) incorrectly recorded, is (are)

(42, 56)

(48, 48)

(66, 33)

(78, 39)

Answer and worked solution

Official answer: C, D

Mirror formula with $f=24$ cm: $\frac1u+\frac1v=\frac1{24}$ .

(42, 56): $\frac1{42}+\frac1{56}=\frac{4+3}{168}=\frac1{24}$ ✓
(48, 48): ✓
(60, 40): $\frac{2+3}{120}=\frac1{24}$ ✓
(66, 33): $\frac{1+2}{66}=\frac1{22}$ ✗
(78, 39): $\frac{1+2}{78}=\frac1{26}$ ✗

An error of 0.2 cm in the image position cannot explain the last two.

(C), (D)

Topics:Focal length measurements Spherical mirrors

← Previous question Next question →

IIT-JEE 2009 · Paper 1, Physics question 50