Waves and Optics - Sound -2

Question 1

Waves and Optics- Sound- Production and Propagation

Describe how sound is produced and propagated in a medium.

Answer 1

Sound is transmitted as a longitudinal wave.

Sound waves are produced by the vibration of particles in solids, liquids and gases.

In the air, the air molecules vibrate and, in turn, push on other air molecules that propagates the process.

Question 2

Waves and Optics- Sound- Production and Propagation
What are compressions?

Answer 2

The areas where molecules are compressed are called compressions.

These compressions move in the direction of the wave carrying energy.

The distance between two compressions is the wavelength.

Question 3

Waves and Optics- Sound- Production and Propagation

What are rarefactions?

Answer 3

Refractions are areas between compressions, in sound waves, where the molecules are spaced out.

Question 4

Waves and Optics- Sound- Production and Propagation
What is Pitch ?

Answer 4

Pitch is the frequency of the sound wave.

Question 5

Waves and Optics- Sound- Production and Propagation
What is Loudness?

Answer 5

Loudness is the amplitude of the sound wave.

Question 6

Waves and Optics- Sound- Production and Propagation
What is the difference between Loudness and Pitch.

Answer 6

Loudness is the amplitude of the Sound wave, whereas, pitch is the frequency of the wave.
A high vibration is a high pitch, whereas, a low vibration is a low pitch.

Question 7

Waves and Optics- Sound- Production and Propagation

What frequencies are detectable by the normal human ear?

Answer 7

The normal human ear can hear in the range of 20 to 20,000Hz.

Question 8

Waves and Optics- Sound- Production and Propagation

What is the average frequency heard by humans ?

Answer 8

150 Hz

Question 9

Waves and Optics- Sound- Speed of Sound
Why is Lightning seen before thunder is heard?
Cite evidence for your theory.

Answer 9

Lightning a scene before Thunder is heard because the speed of light(330 ms^-1) is faster than the speed of sound(3x10^8 ms^-1). Thus we can see the lightning before we hear the Thunder.

Question 10

Waves and Optics- Sound- Speed of Sound

How can we estimate the speed of sound?

Answer 10

The speed of sound can be estimated with the use of echoes.

v= distance/ time
therefore v= 2d/t

We can measure the distance from a speaker and time the amount of time it takes for a sound to be heard from its production.

Question 11

Waves and Optics- Sound- Speed of Sound

What is reflection in the context of sound waves?

Answer 11

Reflection occurs when a wave encounters a plain barrier and experiences a change in its direction only. eg echoes

Question 12

Waves and Optics- Sound- Speed of Sound

What is the Law of Reflection?

Answer 12

The law of reflection:
The angle of incidence (i) [the angle between the normal and the incident wave] is equal to the angle of reflection (r) [the angle between the normal and reflected wave. ]
I = r

Question 13

Waves and Optics- Sound- Speed of Sound

What is refraction ?

Answer 13

Refraction deals with the change of speed [and sometimes direction of a wave] when it’s encounters it change in medium. [from one material/ density two another]

e.g. air to glass
air to water

Question 14

Waves and Optics- Sound- Speed of Sound
When do sound waves move faster?

Answer 14

Sound waves move faster in denser media so the wavelength increases. The frequency stays constant.

Question 15

Waves and Optics- Sound- Speed of Sound
What is Diffraction?

Answer 15

Diffraction is the spreading of waves when it encounters an obstacle or opening of comparable size to its wavelength.

The smaller the opening to the wavelength the greater extent of the fraction.

Wavelength = 2.2 m

Since doors, windows, speaker grills are less than 2.2msound waves are easily diffracted.

Question 16

Waves and Optics- Sound- Speed of Sound
What is superposition ?

Answer 16

Superposition is the addition of two or more waves when they travel in the same region.

When two or more waves overlap, the resulting displacement is the sum of the individual displacement.

Question 17

Waves and Optics- Sound- Speed of Sound
When does constructive and destructive interference occur?

Answer 17

If both waves are in phase then the resultant amplitude is the sum of each. Therefore constructive interference occurs.

If both waves are also phased by 180 degrees then the resultant amplitude is the difference between them. Therefore destructive interference occurs.

eg sound systems

Question 18

Waves and Optics- Sound- Speed of Sound

What is ultrasound and a=what are its uses ?

Answer 18

1. Navigation in: bats, whales and dolphins
2. Sonar to find fish or the seabed. refer to gpn for formula
3. testing for structural weakness or flaws
4. cleaning fabrics and other objects
5. Medical imaging of the human body {cheap to use, no side effects}. The timing of echoes are used to generate images.