An object 4 cm high is placed 15 cm from a concave mirror of focal length 5 cm. The size of the image is?
A
2 cm
B
3 cm
C
4 cm
D
5 cm
Verified Correct Answer: A.
Physical Principles & Numerical Solution
(1)/v + (1)/u = (1)/f
(1)/v + (1)/15 = (1)/5
(1)/v = (1)/5 - (1)/15 = (3 - 1)/15 = (2)/15
∴ v = (15)/2 = 7.5 cm
magnification = (v)/u = (image size)/object size
(7.5)/15 = (X)/4
∴ image size. X = (7.5 x 4)/15 = 2 cm
Source: WAEC / JAMB / NECO Classroom Archive (Record #14327)