Chapter 14 - Sound

Question 1

Define Rarefraction

Answer 1

Used to describe the region where the coils of slinky are pulled apart
Pressure decreases

Question 2

Define compression

Answer 2

Used to describe where the coils of the slinky are pushed together
Pressure increases

Question 3

What type of waves are sound waves

Answer 3

Longitudinal waves

Question 4

When are sound waves produced

Answer 4

When objects vibrate

Question 5

Explain what happens in the bell jar experiment

Answer 5

When the Bung is off the bell jar you can hear the bell ring
When the Bung is on the bell jar you cannot hear the bell ring
Why: - no air inside jar
- sounds cannot be carried to the sides of the jar
- bell cannot be heard but gong can be seen
- impossible for sound waves to travel through a vacuum as no air particles to carry particles from place to place

Question 6

Why can we hear sounds

Answer 6

Sound waves carry energy through the air
Causes other objects like our eardrums to vibrate
Vibrayions are converted into electrical signals and carry to the hearing centre via the auditory nerve

Question 7

How are echoes made

Answer 7

When a sound waves reflects off a smooth hard surface suck as a brick wall or mountain

Question 8

What is the frequency range for a normal human convorsation

Answer 8

800Hz

Question 9

What frequencies can humans not hear above

Answer 9

20,000Hz

Question 10

Explain measuring the speed of sound using echoes

Answer 10

• bang 2 pieces of wood together
• get a friend to stand far away
• measure the time you see the bricks hit each other and when you hear the sound
• reaction time means inaccurate
• divide distance by time to work out speed

Question 11

Measuring the speed of sound with resonance tube and tuning fork

Answer 11

• when air vibrates in a tube the sound wave is reflected, the reflected wave reinforces the original, gives waves larger amplitude-> RESONANCE (think of skipping rope attached to wall and spinning it)
• resonance tube is a Perspex tube with a reservoir, when you change the height of water the length of tube changes as sound waves are reflected at water surface.
• to make a sound of a know frequency you strike a tuning fork and hold it above open end of tube. The water column is adjusted when loudest sound is heard
• the first resonance is heard when the length of air in the tube is equal to a quarter of the wavelengt.

Question 12

Measuring speed of sound using oscilloscope

Answer 12

• set the signal generator to give a frequency of 1KHz
• start with microphones together and compare the lines on the oscilloscope
• continue to move the microphones further away from each other, so it is one whole wavelength away from each other.( you can tell by the traces are exactly one above another)
• measure the distance between the microphones to get the wavelength and use the oscilloscope to find the accurate value for the frequency

Question 13

Define frequency

Answer 13

The number of waves passing a particular point each second

Units - Hz = Hz=S^-1

Question 14

What is pitch

Answer 14

The frequency of musical instruments

Question 15

Why can’t we hear explosions in space

Answer 15

No air particles

Sound cannot travel through a vacuum