JAMB Physics 2013 Paper

Concept:A pinhole camera forms an image by similar triangles, so the image height is proportional to the image distance divided by the object distance.Explanation:Use the magnification formula for a pinhole camera, where $h_o$ is object height, $h_i$ is image height, $u$ is object distance from the pinhole, and $v$ is the distance from the pinhole to the screen.$$\frac{h_i}{h_o} = \frac{v}{u}$$So, $h_i = \frac{h_o \times v}{u}$.Substitute the given values: $h_o = 1.5\,\text{m}$, $v = 0.1\,\text{m}$, $u = 3\,\text{m}$.$$h_i = \frac{1.5 \times 0.1}{3}$$$$h_i = \frac{0.15}{3} = 0.05\,\text{m}$$Answer:The height of the image is $0.05\,\text{m}$, which is option A.