Albert Teen YOU ARE LEARNING:  Period and Frequency  # 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.

1

Imagine a rope that is held a both ends

If you jerk the rope upwards just once, it creates a pulse. 2

If you jerk the rope up and down continuously it produces a _____________ __________.  3

True or false? Periodic waves are made of recurring pulses.  4

So what does "periodic" mean?

It means having regular, recurring cycles. Waves are "periodic" because they have regular intervals of oscillations. 1

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  2

What unit do you think you should use for the time period of a wave?  3

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). 1

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. 2

Which of these waves transfer more energy? Answer A or B.  3

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. What do you think we measure frequency in? Calculating frequency

1

Say the time period for a wave is $0.25 \space s$. What does that mean? 2

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? 3

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

1

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? 2

There is also a shorter way to write the formula for frequency $frequency = \frac{1}{time \space period}$ . Which one? 3

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

1

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? 2

So the frequency is 2 Hz. What does that mean the time period is? Summary

1

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).

2

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.

3

The unit for frequency is Hertz (Hz)

Hertz is the same as $1/s$