§5.4 + §5.5 — answers

• Natuurkunde / Scheikunde
• Middelbare school
• havo, vwo
• Leerjaar 1

The answers

Go through the answers one by one, compare your answer to the answers in this presentation.

If you have any questions about them, ask mr. Brands to join.

Recap last week.

How many waves do you count in each image?

Image 1 — 4 waves

Image 2 — 2 waves

One square is 3 cm long, what is the wave length of the waves in each image?

Image 1 — 6 cm

Image 2 — 12 cm

One square is 3 cm, what is the amplitude of the wave below?

6 cm

In a soundwave the air (or another medium) actually doesn't go up and down. 

What do the ups and down in the visual depiction of a wave indicate about the air?

In a sound wave the air gets comprsessed together and then decompresed. The peaks indicates areas of compression. The valleys indicate areas of decompression.

As seen in the image on the right.

Of these two sound waves, which will produce a louder sound? Explain.

Image 1

Image 2

The sound wave in image two, because it has a bigger amplitude than the one in image 1.

What is the amplitude of a wave? how does it influcece the sound a soundwave produces? 

What is wavelength of a wave?

The distance from a peak or valley of a wave to the center. The larger the amplitude of a soundwave, the louder the sound it  produces is.

The distance from the beginning to the end of a wave.

§5.5 Pitch and frequency

Which of these two audio samples has the highest pitch?

Audio sample A

Audio sample B

Which of thes two sound waves has a hihger frequency?

Wave 1

Wave 2

Which wave would produce which sound? match them.

Wave 1

wave 2

Audio sample A

Audio sample B

What is the relationship between pitch and frequency?

The higher the frequency the higher the pitch

• What is frequency? What is the unit of frequency? Explain in your own words.  The amount of waves per second. The unit of frequency is hertz (Hz).

• What is the difference between amplitude and frequency? The amplitude is the distance from the peak/valley to the center where the frequency is the amount of waves per second.

• How does the amplitude of a soundwave influence the sound it makes? How does the frequency of a soundwave infuence the sound it makes? The amplitude influences how loud the sound is. The frequency influences the pitch of the sound

Calculations

See the two images below. in both images 8 milliseconds go by.

a) How many waves are there in one second in each image?

b) what is the frequency of the waves in each image?

Image 1

Image 2

a) There are 1000 milliseconds in one second. In each image 8 miliseconds go by. 

1000/8 is 125 (so the images show 1/125hth of one second) . 

In image one there are two waves in these 8 miliseconds. That means that in one second there are 2 x 125 = 250 waves.

In image two there are 6 wave in these 8 miliseconds. That means that in one second there are 6 x 125 = 750 waves per second

See the two images below. in both images 8 milliseconds go by.

a) How many waves are there in one second in each image?

b) what is the frequency of the waves in each image?

Image 1

Image 2

b) 

Image one shows a wave that has 250 waves per second. That means that it has frequency of 250 Hz.

Image two shows a wave that has 750 waves per second. That means that it has frequency of 750 Hz.

See the images below. in both images 8 milliseconds go by.

What is the frequency of this wave? use the formula 

f=​T​​1​​

Given

T = 2 milliseconds = 0.002 seconds.

Asked

What is the frequency?

Formula

Calculation

f = 1/T = 1/0.002 =500 Hz

f=​T​​1​​

A speaker produces a sound wave of 18 Hz. 

a) Would you hear any sound from it? Explain. No the frequenc is to low for humans to hear.

b) Would an elephant hear any sound from it? Explain. An elephant can hear up to under 16 Hz and so would be able to hear a sound of 18 Hz.

c) You decide to let the speaker play a higher frequency. How high could you go so that we can still hear it? 20000 Hz Because humans can only hear up to 20000 Hz.

Done?

Start with § 5.6