Waves

YOU ARE LEARNING:

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 $1/s$