Final answer:
A semidiurnal period is related to a tidal day by being half the duration of a tidal day. This indicates that there are two cycles of high and low tides within one tidal day, resulting in each semidiurnal cycle occurring roughly every 12.25 hours.
Step-by-step explanation:
Relationship Between Semidiurnal Period and Tidal Day
The term “semidiurnal” refers to events that happen twice within a specified period. In terms of tides, a semidiurnal period means that there are two high tides and two low tides within a tidal day. A tidal day is slightly longer than a solar day, typically about 24 hours and 50 minutes, due to the relative motion of the Earth and Moon. Since the Earth rotates underneath the tidal bulges created by the moon's gravitational pull, we experience regular changes in sea level known as tides. The duration of a semidiurnal period is therefore half the duration of a tidal day because one experiences two cycles of high and low tides in one tidal day.
The correct answer to the question “How is a semidiurnal period related to a tidal day?” is B. Half the duration. This means that each semidiurnal cycle (one complete cycle of high and low tide) occurs about every 12.25 hours, which is roughly half of a tidal day.