What is Sound?

Question 1

Definition of Sound

Answer 1

Sound is a form of energy that is transferred from one point to another as a longitudinal wave.

Question 2

How is sound produced?

Answer 2

Sound is produced by vibrating sources placed in a medium. The medium is usually air, but it can be any gas, liquid or solid.

Question 3

How does a sound wave propagate?

Answer 3

An object vibrating in air caused the layers of air particles around it to be displaced. This displacement of particles causes sound waves to propagate.

Question 4

Compressions

Answer 4

are regions where air pressure is HIGHER than the surrounding air pressure

Question 5

Rarefractions

Answer 5

are regions where air pressure is LOWER than the surrounding air pressure

Question 6

Sound waves need a medium to travel from one point to another/for transmission.

Answer 6

Speed of sound differs in:

gas

Question 7

Direct method of measuring the

speed of sound in air

Answer 7

Procedure:

1. Using a measuring tape, observers A and B are positioned at a known distance d apart in an open field.
2. Observer A fires a starting pistol
3. On seeing the flash of the starting pistol, observer B starts the stopwatch and then stops it when he hears the sound. The time interval t is then recorded

Calculation:
d=800m, t=2.4s
speed of sound in air v= d/t
=800/2.4
=333m/s

Accuracy can be increased:

1. Repeat the experiment a few times and calculate the average value of v. Taking the average minimised the random errors that may occur while timing the interval.
2. Repeat the experiment but with the observers A & B interchanged. This cancels the effect of wind on v.

Question 8

Definition of echo

Answer 8

An echo is the repetition of a sound due to the reflection of sound.

Question 9

Formation of an echo

Answer 9

An echo is formed when a sound is reflected off hard, flat surfaces, such as a large wall or distant cliff. The laws of reflection of light also apply to sound waves.

Ear detects loudest reflected sound when angle of i=r

Question 10

Uses of echoes

Answer 10

Measure distances
- depth of the sea can be found by sending out a signal and noting the time interval before the reflected signal (echo) arrives.

Question 11

Definition of Ultrasound

Answer 11

Ultrasound is sound with frequencies ABOVE the upper limit of the human range of audibility.

Question 12

Uses of ultrasound

Answer 12

Quality control
•Manufacturers of concrete use ultrasound to check for cracks/cavities in concrete slabs. (if there’s no signal, there’s a crack. if the sound bounced back and signal, there’s no crack)

1. Ultrasound emerges from a transmitter.
2. Ultrasound passes through the concrete slab and is received by a sensor.
3. By comparing the ultrasound emitted and received, the presence and location of defects can be identified.

Prenatal scanning
•Ultrasound can be used to obtain images of structures in the body: examine the development of foetuses
•less hazardous than x-rays due to its lower energy
•ultrasound pulses are sent into the womb via a transmitter. by measuring the time taken for the ultrasound pulses to be reflected, the depth of the reflecting surface within the womb can be derived, forming an image.

Question 13

Pitch

Answer 13

The higher the frequency of a sound wave, the higher the pitch.

shorter wavelength=higher frequency=higher pitch

longer wavelength=lower frequency=lower pitch

Question 14

Loudness

Answer 14

The larger the amplitude of a sound wave, the louder the sound.

Question 15

Explain why the pulse that is received is weaker than the pulse that was sent out.

Answer 15

As the sound wave moves in the water and is REFLECTED OFF the sea bed, SOME of its ENERGY will be LOST. Thus the reflected sound wave will be weaker.

Question 16

Explain why the pulse that is received is weaker than the pulse that was sent out.

Answer 16

As the sound wave moves in the water and is REFLECTED OFF the sea bed, SOME of its ENERGY will be LOST. Thus the reflected sound wave will be weaker.