Sound (Cambridge O Level Physics)

When objects vibrate, they produce sound waves.

An object in a room vibrates. However, a person in that same room does not hear anything. Why not?

After a lockdown drill at a school, the management team notes that the lockdown siren is too quiet, and its pitch is too low to be heard at a distance.

They call the company that supplied the siren and ask them to make the alarm louder, and to give it a higher pitch.

What effect does the change have on the resulting sound wave produced by the siren?

A teacher uses a piece of lab equipment called a signal generator, which he connects to a speaker.

This apparatus can be used to make a particularly irritating noise.

The teacher makes four sounds of different frequencies with the signal generator. Which one can be heard by the student?

Echoes can sometimes be heard where a person is surrounded by distant, hard, flat surfaces.

In Greek mythology, Echo is a mountain nymph who was cursed by Hera to be only able to repeat the last words she heard. This ends tragically when she falls in love with Narcissus who, alas, loves only his own reflection.

In Physics, which wave property causes an echo?

A boy named Narcissus participates in a class experiment to measure the speed of sound. He finds the large, flat wall of a building and stands a known distance away from it. He then claps his hands.

A very short time later, he hears the sound of the clap returning to him as an echo.

Why?

The depth of the sea under a ship is determined by sending a pulse of sound with a frequency of 3000 Hz from a transmitter on the bottom of the ship to the seabed. The sound reflects from the seabed and returns to a receiver on the bottom of the ship.

The time between sending the pulse and receiving the reflected pulse is measured

The depth of the sea beneath the ship is 600 m and the time measured is 0.80 s.

What is the wavelength of this sound in the sea?

The sound from a ship is reflected by a cliff. An echo is heard by a sailor on the ship 4.0 s after the sound is made. The speed of sound in air is 320 m/s. 

How far from the cliff is the ship?

In a common secondary school demonstration, a speaker is placed next to a lighted match.

A loud sound wave is played through the speaker, causing the flame to vibrate.

What type of wave is emitted from the speaker, and in which direction does the flame vibrate?

A fishing boat uses sonar to locate a shoal of fish. The sonar system sends a pulse of sound towards the shoal. When it hits the shoal, the sound wave is reflected and picked up by a detector underneath the ship.

The speed of sound in water is 1500 m/s.

The pulse of sound waves is received 0.48 s after it is emitted. 

How far from the boat is the shoal of fish?

In the olympic 100 m sprint final, a starting pistol is used to tell the sprinters when to start.

A spectator, sitting in the viewing area 300 m away sees the smoke from the pistol 0.86 s before hearing the bang. The spectator has exceptionally keen reactions and a very accurate internal clock.

Using only this information, what is the speed of sound in air?

A walker can see a cliff face some distance away, and wants to estimate how far away it is.

He makes a loud noise, and times how long it takes the echo to come back. It takes 1.8 s.

If the speed of sound is 345 m/s, how far away is the cliff?

Ultrasound is high-pitched and cannot usually be heard by human ears. However, ultrasound does have many uses.

Which statement, or statements, in the list below are correct uses of ultrasound?

1. Testing materials to find breaks or other damage
2. Medical scanning of organs and soft tissues
3. Radar systems to find distance and velocity