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# 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**.

If you jerk the rope up and down continuously it produces a _____________ __________.

True or false? *Periodic waves are made of recurring pulses.*

So what does "periodic" mean?

It means having **regular**, **recurring** cycles. Waves are "periodic" because they have regular intervals of oscillations.

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

What unit do you think you should use for the time period of a wave?

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).

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.

Which of these waves transfer more energy? Answer A or B.

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.

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 $0.25 \space s$. What does that mean?

So it takes this wave $0.25 \space s$ 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 $\frac{1 \space s}{0.25 \space s}=4 \space Hz$. So what is the correct formula for frequency?

There is also a shorter way to write the formula for frequency $frequency = \frac{1}{time \space period}$ . Which one?

The unit for frequency is $Hz$ and the unit for time period is $s$ so actually Hertz is the same as...

$f= \frac {1}{T}$, 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 $f=\frac{1}{T}$ where $f$ is frequency and $T$ is time period.

The unit for frequency is Hertz (Hz)

Hertz is the same as $1/s$