WAEC Physics 2018 Paper

Concept:For a wire fixed at both ends, the fundamental frequency corresponds to a standing wave with wavelength $\lambda = 2L$.Explanation:The wire length is given as $L = 400\ \text{cm}$.Convert this to metres: $L = 400\ \text{cm} = 4\ \text{m}$.The relationship between wave speed $v$, fundamental frequency $f_0$, and length $L$ is $f_0 = \dfrac{v}{2L}$.Substitute the known values: $150 = \dfrac{v}{2 \times 4}$.This gives $150 = \dfrac{v}{8}$.Rearrange to solve for $v$: $v = 150 \times 8 = 1200\ \mathrm{ms}^{-1}$.This matches option C.Answer:The speed of the wave produced is $1200\ \mathrm{ms}^{-1}$, i.e. option C.