JAMB Physics 2023 Paper

Concept:A convex mirror always forms a virtual, diminished image behind the mirror.So the image distance is expected to have a negative sign using the real-is-positive sign convention.Explanation:Use the mirror formula: $\frac{1}{f} = \frac{1}{u} + \frac{1}{v}$.For a convex mirror, the focal length is taken as negative: $f = -15 \, \text{cm}$.The object is real, placed in front of the mirror, so $u = 35 \, \text{cm}$.Substituting into the formula gives: $\frac{1}{-15} = \frac{1}{35} + \frac{1}{v}$.Rearrange: $\frac{1}{v} = -\frac{1}{15} - \frac{1}{35}$.Compute: $\frac{1}{v} = -\frac{35 + 15}{525} = -\frac{50}{525} = -\frac{2}{21}$.Therefore, $v = -\frac{21}{2} = -10.5 \, \text{cm}$.The negative value shows the image is virtual and located behind the mirror.Answer:B. 10.5 cm behind the mirror.