Q. A book can be read if it is placed at a distance of 50 cm from a source of 1 cd. At what distance should the book placed if the source is of 16 cd?
A) 8 m
B) 4 m
C) 2 m
D) 1 m
Explanation
(c) $\frac{1}{50^{2}} = \frac{16}{d^{2}}$
Or ${\ d}^{2} = (50)^{2} \times 16$
Or $\ d = 50 \times 4$cm = 200cm = 2m
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.