Calculate with sound

Calculate with sound
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Slide 1: Slide
physicsMiddelbare schoolhavo, vwoLeerjaar 2

This lesson contains 19 slides, with text slides.

time-iconLesson duration is: 45 min

Items in this lesson

Calculate with sound

Slide 1 - Slide

Formulas:
f = 1/T
T = period in s
f = frequency in Hz
T = 1/f
f = frequency in Hz
T = period in s
Converting
ms to s (: 1000)

kHz to Hz (x 1000)
Hz to kHz (:1000)
s = v x t
v = speed in m/s
t = time in s
s = distance in m

Slide 2 - Slide

1. Calculate
time/div = 0.2 ms/div
Calculate the frequency

Slide 3 - Slide

2. Tones
a. Which picture shows the highest tone?
b. Which picture shows the lowest tone?
c. Which picture shows the loudest tone?

Slide 4 - Slide

3. 
You see a musical box. When you rotate the handle, you hear a melody.
a. Which bars produce the lowest tones, the short or the long ones?
b. Which bars produce the highest tones?

Slide 5 - Slide

4. Oscilloscope
a. Read the period of one vibration (click on picture to enlarge).
b. Calculate the frequency.

Slide 6 - Slide

5. Piano
A piano string produces vibrations with a period of 2.5 ms.
a. Convert the period into seconds.
b. What is the frequency f?
c. Convert the frequency to kHz.

Slide 7 - Slide

6. Air-raid siren
This is an old fashioned air-raid siren. Air is driven via a tube onto the rotating disc. The air is forced through 30 holes in the disc. This creates a vibration which produces a loud sound. The disc rotates 5 times per second.

Slide 8 - Slide

6.
a. How many times per second does a hole appear below the opening of the air pipe?
b. Explain why you hear a tone of 150 Hz

Slide 9 - Slide

6
The siren starts slowly and the gradually becomes higher. At full speed the tone is 1.8 kHz.
c. Calculate the periode of this frequency.
d. How many times per second does the disc rotate now?

Slide 10 - Slide

7
At a firework display, Phil sees a rocket explode 124 m above his head. The sound of speed is 340 m/s. 
Calculate how much later Phil hears the bang.

Slide 11 - Slide

1.
Given: 0.2 ms/div
1 vibration is 5 blocks (div)
Asked: f
Solution: f = 1/T
T = 5 x 0.2 ms = 1 ms
1 ms :1000 = 0.001 s
f = 1 / 0.001 s = 1000 Hz

Slide 12 - Slide

2.
a.  C- most vibrations in 0.01 s
b. B- least amount of vibrations in 0.01 s
c. A - biggest displacement (in y-direction) 

Slide 13 - Slide

3.
a. The longest ones
b. The shortest ones

Slide 14 - Slide

4. 
a. One vibration lasts 1.82 ms (easiest to see from 6 to 7.82 ms)
b. Given: T = 1.82 ms = 1.82:1000 = 0.00182 s
Asked: f
Solution: f = 1/T
f = 1 / 0.00182 = 549,5 Hz

Slide 15 - Slide

5.
a. T= 2.5 ms = 2.5 : 1000 = 0.0025 s
b. Given: T = 0.0025 s
Asked: f
Solution: f = 1/T
f = 1/ 0.0025 = 400 Hz
c. f = 400 Hz = 400 : 1000 = 0.4 kHz

Slide 16 - Slide

6
a. The disc turns 5 times per second. 5 Times the 30 holes in the disc are 150 holes. 150 Holes pass the air pipe per second.

b. Every time the air is blown into the hole and then interrupted by the solid part in between the holes, creates a sound. This happens 150 times per second = at a frequency of 150 Hertz.

Slide 17 - Slide

6
c. f = 1.8 kHz = 1.8 kHz x 1000 = 1800 Hz
d. Given f = 1800 Hz
30 holes in the disc
Asked: amount of rotations per second
Solution: 1800 holes pas per second
1800 : 30 holes per rotation = 60 rotations per second

Slide 18 - Slide

7
Given: s (distance) = 124 m
v (speed) = 340 m/s
Asked: t (time)
Solution: s = v x t
t = s / v = 124 m / 340 m/s = 0.36 seconds

Phil hears the blast after 0.36 seconds.

Slide 19 - Slide