Science (Physics): Sound

Sound

by Mr Wang

Multiple Choice

A series of compressions and rarefactions of a sound wave is shown. What is the wavelength of the wave?

• 3.0 m

• 4.0 m

• 9.0 m

• 12 m

​Can sound travel in vacuum?

​Sound cannot travel through a vacuum.

​

​Sound needs a medium for transmission.

Multiple Choice

Which of the following is not possible? 

• A man knocks at one end of a long metal pipe and another man hears the knock at the other end.

• An explosion is heard by an astronaut when a laser beam hits an enemy fighter in space.

• A whale hears another whale in the deep sea.

• A mole hears another mole underground.

​Measuring the speed of sound in air

​Person A and B are positioned at a large distance apart. Person A fires the starting pistol and when Person B sees the flare of the starting pistol, he starts the stopwatch.

​Person B stops the stopwatch when he hears the sound of the pistol.

​

​The time interval is recorded.

​

​The assumption used in this method is that the time taken for light to travel the distance is negligible because light travels at a very high speed.

​The result can be improved in 2 ways:

​Repeat the experiment a few times and compute the speed of sound each time. Find the average value. (This will reduce the human errors)

​

​Observers A and B should exchange positions and repeat the experiment.

Multiple Choice

In an experiment to determine the speed of sound, a gun was fired and an observer 900 m away measured the time interval between seeing the flash of the gun and hearing the shot. The duration indicated by a stopwatch is 2.5 s. What is the speed of sound in the air?

• 300 m/s

• 330 m/s

• 360 m/s

• 390 m/s

​How are Echoes formed?

​An echo is formed when a sound is reflected off a flat surface such as a large wall.

​

​The echo has the frequency of the original sound but is softer.

​

​Echoes obey the Law of Reflection

​

​The angle of incidence i is equal to the angle of reflection r.

Multiple Choice

A sound wave is reflected from a wall. Which of the following about the echo is true?

• It has a lower speed.

• It has a lower frequency.

• It has a shorter wavelength.

• It has a smaller amplitude.

Multiple Choice

A sonar signal from a ship is sent underwater towards the sea bed. It takes 0.7s for the signal to bounce back from the sea bed. If sound travels at 1500 m/s in water, how deep is the sea?

• 525 m

• 1050 m

• 1071 m

• 2143 m

​Loudness & Pitch

​Loudness is a sensation related to the amplitude of a sound wave. The larger the amplitude, the louder the sound.

​

​Pitch is a sensation related to the frequency of a sound wave. The higher the frequency, the higher the pitch.

Multiple Choice

Which of the sound waves below is the loudest?

Multiple Choice

Which of the sound waves below has the highest pitch?