WAEC Physics 2015 Paper

Concept:A diverging lens has a negative focal length, and the lens formula is used to find the image distance.Explanation:For a diverging lens, the focal length is taken as negative. Given: $f = -12\text{ cm}$ and $u = 15\text{ cm}$.The lens formula is: $f = \frac{uv}{u+v}$Substitute the known values: $-12 = \frac{15v}{15+v}$Cross-multiply to remove the fraction: $-12(15+v) = 15v$ $-180 - 12v = 15v$ $-180 = 15v + 12v$ $-180 = 27v$Solve for $v$: $v = \frac{-180}{27} = -6.67\text{ cm}$The negative sign of $v$ means the image is formed on the same side as the object. Hence, the image is virtual and located $6.67\text{ cm}$ from the lens.Answer:B. virtual and 6.67 cm from the lens.