A student performed the experiment of determination of focal length of a concave mirror by (u-v) method using an optical bench of length `1.5m`. 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),(60,33),(78,39)`. the data set (s) that cannot come from experiment and is (are) incorrectly recorded, is (are)
(a) `(42,56)`
(b)`(48,48)`
(c)` (66,33)`
(d) `(78,39)`.

Options

A. (42,56)
B. (48,48)
C. (66,33)
D. (78,39)

Answer

C, D

Explanation

By using mirror formla `(1)/(v)+(1)/(u)=(1)/(f)`
Set `1 rarr u = -42 cm rArr v = -56 cm`
Set `2 rarr u = -48 cm rArr v = -48 cm`
Set `3 rarr u = -60 cm rArr v = - 40 cm`
Set `4 rarr u = -66 vm rArr v = -37.7 pm 0.2 ne 33 cm`
Set `5 rarr u = -78 rArr v = -34.67 pm 0.2 ne 39 cm`.