A needle of length 4.5 cm is placed vertically 12 cm away from a convex mirror of focal length 15 cm. The magnification of the image produced is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( 5/9 \)
Use the mirror formula and then the magnification \( m = -v/u \). With the Cartesian sign convention (distances measured from the pole, negative on the object side), the object distance is negative and the focal length of a convex mirror is positive.
\( u = -12\,\mathrm{cm} \)
\( f = +15\,\mathrm{cm} \)
\( \displaystyle \frac{1}{v} = \frac{1}{f} - \frac{1}{u} = \frac{1}{15} + \frac{1}{12} = \frac{4 + 5}{60} = \frac{9}{60} \)
\( \displaystyle v = \frac{60}{9}\,\mathrm{cm} \approx 6.67\,\mathrm{cm} \)
\( \displaystyle m = -\frac{v}{u} = -\frac{60/9}{-12} = \frac{5}{9} \)
The positive sign means an erect, virtual image, as a convex mirror always gives.
Note: This question is from NCERT (2026-27). NTA sets numerical questions from NCERT too, so do not ignore NCERT while practising numericals.
NCERT (2026-27):
Exercises – …
