Option C is correct. Frequency can be found by counting the number of troughs per second in a wave diagram.
Frequency is defined as the number of repetitions of waves occurring in 1 second. It can also be said that Frequency is defined as the number of cycles completed in 1 second.
Frequency is given by the formula as,
[tex]\rm f=\frac{1}{t}[/tex] Hz.
Hence option C is correct. Frequency can be found by counting the number of troughs per second in a wave diagram.
To learn more about the frequency refer to the link;
https://brainly.com/question/4393505
