c$)$ Vision. When light having vibrations with angular frequency ranging from to strikes the retina of the eye, it stimulates the receptor cells there and is perceived as visible light. What are the limits of the period and frequency of this light? $($d$)$ Ultrasound. High$-$frequency sound waves $($ultrasound$)$ are used to probe the interior of the body, much as x rays do$.$ To detect small objects such as tumors, a frequency of around $5\mathrm{.}0$ MHz is used. What are the period and angular frequency of the molecular vibrations caused by this pulse of sound?