YOU ARE LEARNING:
Period and Frequency
Period and Frequency
The time period of a wave is the time it takes for one cycle to be completed. The frequency is how many cycles are completed in one second.
Imagine a rope that is held a both ends
If you jerk the rope upwards just once, it creates a pulse.
![](https://cdn.hejalbert.se/teen/blocks-images/en_GB/GJuSLdfKThO5ZfKMxj7h.png)
If you jerk the rope up and down continuously it produces a _____________ __________.
![](https://cdn.hejalbert.se/teen/blocks-images/en_GB/Mh4VNZrIRZS4tZsXsoxc.png)
True or false? Periodic waves are made of recurring pulses.
![](https://cdn.hejalbert.se/teen/blocks-images/en_GB/Mh4VNZrIRZS4tZsXsoxc.png)
So what does "periodic" mean?
It means having regular, recurring cycles. Waves are "periodic" because they have regular intervals of oscillations.
![](https://cdn.hejalbert.se/teen/blocks-images/en_GB/Mh4VNZrIRZS4tZsXsoxc.png)
What do you think we mean when we talk about the period of a wave?
A) Life time of the wave B) Time for a pulse to reach the end of the medium C) Time for one cycle to be completed
![](https://cdn.hejalbert.se/teen/blocks-images/en_GB/reJEfPmdTqxNm3BRJ5GQ.png)
What unit do you think you should use for the time period of a wave?
![](https://cdn.hejalbert.se/teen/blocks-images/en_GB/reJEfPmdTqxNm3BRJ5GQ.png)
So what is the period of a wave?
It is the time it takes to complete one vibrational cycle of a wave. It is measured in seconds (s).
![](https://cdn.hejalbert.se/teen/blocks-images/en_GB/reJEfPmdTqxNm3BRJ5GQ.png)
A wave's frequency relates to how much energy it transfers
The more wavelengths pass a specific point (X) per second, the more energy the wave transfers.
![](https://cdn.hejalbert.se/teen/blocks-images/en_GB/vlvbEherT3m6lNaAlrdq.png)
Which of these waves transfer more energy? Answer A or B.
![](https://cdn.hejalbert.se/teen/blocks-images/en_GB/vlvbEherT3m6lNaAlrdq.png)
So wave B has more energy and also higher frequency than wave A
More wavelengths would pass point X per second for wave B, compared to wave A.
![](https://cdn.hejalbert.se/teen/blocks-images/en_GB/vlvbEherT3m6lNaAlrdq.png)
Pick all the options that are correct descriptions of what a wave's frequency is.
You can select multiple answers
What do you think we measure frequency in?
Calculating frequency
Say the time period for a wave is 0.25 s. What does that mean?
So it takes this wave 0.25 s to complete one vibrational cycle. How many wavelengths will pass a specific point in 1 second, then?
Frequency is the number of wavelengths that pass a point in one second. So what is the frequency of this wave? Give your answer in Hertz (Hz).
Formula for frequency
You just calculated the frequency like this 0.25 s1 s=4 Hz. So what is the correct formula for frequency?
There is also a shorter way to write the formula for frequency frequency=time period1 . Which one?
The unit for frequency is Hz and the unit for time period is s so actually Hertz is the same as...
f=T1, so what is the formula for time period?
An example
A person holding a rope moves their hand up and down and produces 2 waves per second. What is the frequency of the wave produced?
So the frequency is 2 Hz. What does that mean the time period is?
Summary
The time period of a wave is how long it takes for one vibrational cycle to be completed
You can also think if it as the time it takes for one wavelength to pass a specific point. It's measured in seconds (s).
Frequency is how many wavelengths pass a certain point per second
It's calculated like this f=T1 where f is frequency and T is time period.
The unit for frequency is Hertz (Hz)
Hertz is the same as 1/s