Resonans av lydbølger – problemer og løsninger

1. Etter at stemmegaffelen A vibreres, vibreres stemmegaffelen B. Stemmegaffelen B vibreres fordi…..

A. Stemmegaffelen A har samme amplitude som stemmegaffelen B

B. Begge stemmegaflene bruker samme resonansboks

C. Stemmegaffelen B har samme frekvens som stemmegaffelen A

D. Klangfargen til lydene forårsaket av begge stemmegaflene er den samme

Oppløsning

After vibrated, the tuning fork A vibrates the surrounding air, so the air also vibrates with the same frekvens. Furthermore, the air vibrates the tuning fork B. The tuning fork B is also vibrating with natural frequency, but the amplitude of the vibration is minimal, and the vibration is not visible. Since the natural frequency of the tuning fork B is equal to the frequency of the air vibration,

and the frequency of the tuning fork A, then the air molecule amplifies the amplitude of the tuning fork B. The tuning fork B appears to vibrate because its amplitude of vibration is visible.

Riktig svar er C.

2. A resonans tube produces a loud sound at the first time when the length of the air column is 17 cm and a loud sound at the second time when the length of the air column is 51 cm. The tuning fork frequency used is 500 Hz. Determine the speed of the air in the tube.

A. 138 m/s

B. 230 m/s

C. 340 m/s

D. 461 m/s

løsning:

The shape of the resonance tube is one end is open, and the other end is closed, so the distance between the node and anti-node = the minimum length of tube = ¼ λ = λ / 4.

The equation of the length of the tube :

The distance between the node and an anti-node of the tube of resonance with one end is open, and another end is closed, fulfilled when n is an odd number

Det riktige svaret er C.

3. The first resonance in the tube of resonance occurs when the length of the air column is 20 cm. The second resonance and the third resonance happen when the length of the air column is…

A. 40 cm and 60 cm

B. 30 cm and 40 cm

C. 60 cm and 100 cm

D. 100 cm and 200 cm

Kjent:

The length of the air column if n₁ = 1 (L₁) = 0.2 meter

Ønskes: The length of the air column if n₂ = 3 og n₃ = 5

løsning:

The equation of the length of the tube (equation of the length of air column) :

Use this equation to calculate the bølgelengde using the above data :

The length of the air column when n₂ = 3:

Riktig svar er C.