Both of the first two statements are true:
- It is proper to use the period when it is 1 second or greater. The period is the time it takes for one complete cycle of a wave to occur, and it is typically measured in seconds. When dealing with waves that have periods of 1 second or longer, it is more convenient to use the period rather than the frequency.
- It is proper to use the frequency when it is 1 Hertz or greater. The frequency is the number of cycles of a wave that occur in one second, and it is typically measured in Hertz (Hz). When dealing with waves that have frequencies of 1 Hz or higher, it is more convenient to use the frequency rather than the period.
The last two statements are not true:
- It is not proper to use the period when it is less than 1 second. The period is still a valid measure for waves with periods less than 1 second, but it may be more convenient to use the frequency instead.
- It is not proper to use the frequency when it is less than 1 Hertz. The frequency is still a valid measure for waves with frequencies less than 1 Hz, but it may be more convenient to use the period instead.