Waves and Sounds

Question 1

What does a wave carry?

Answer 1

Energy, with no transport of matter.

Question 2

What are the two classifications of waves?

Answer 2

Mechanical or electromagnetic.

Question 3

What are mechanical waves?

Answer 3

Produced by a disturbance in a mechanical medium and are transmitted by particles of the medium oscillating to and fro.

They can be felt and include waves of a spring, water waves and sound waves.

Question 4

How are spherical waves produced ?

Answer 4

Dropping an object into a body of water.

Question 5

How are parallel plane waves produced?

Answer 5

By dipping a straight edged object into water.

Question 6

What are progressive (travelling) waves?

Answer 6

Consist of a disturbance moving from a source to surrounding places as a result of which, energy is transferred from one point to another.

Question 7

What are the two types of progressive wave?

Answer 7

Transverse (particles move back and forth perpendicular to the direction of the wave).

Longitudinal (particles move back and forth in the same direction as the wave. Consist of a series compressions and refractions.

Question 8

What are Hertz ? (Hz)

Answer 8

The unit of frequency in the case of waves with periodic motion.

Question 9

What is the intensity (I) of a wave?

Answer 9

The rate at which the wave transports energy per unit area perpendicular to its direction of motion.

Proportional to the square of its frequency and square of its amplitude.

Question 10

What is a stationary (standing) wave?

Answer 10

A wave that appears to not be travelling in either direction due to repeated progressive reflections in the waves travelling in opposite directions.

Question 11

What are the nodes of a standing wave?

Answer 11

Where the displacement is always zero.

Question 12

What are the antinodes of a standing wave?

Answer 12

The points where displacement is at maximum.

Question 13

What are sound waves ?

Answer 13

Longitudinal waves that consist of varying pressures.

They can travel through solids, liquids and gases.

They consist of regions of compression and rarefaction that follow each other, due to medium becoming alternately squeezed and expanded as it passes a point.

Question 14

What is the speed of sound?

Answer 14

343m/s In air at 1atm and 20°C

Question 15

What is Mach Number?

Answer 15

Mach = True aircraft speed / local speed of sound

Question 16

What is loudness ?

Answer 16

A subjective sensation determined by the intensity of the sound and sensitivity of the observer’s ear.

Question 17

What is pitch?

Answer 17

A sensation experienced by the listener.

Below 1000Hz the pitch is slightly higher than the frequency.

Question 18

What is the Doppler effect ?

Answer 18

The pitch of the note of siren appears to suddenly drop in frequency as the sound source passes by at a fast speed.

Question 19

How does the Doppler effect occur?

Answer 19

As the source approaches the listener, the wavelengths are shorter than when there is no relative motion (effectively travelling behind the vehicle ) , leading to a higher pitched sound from a higher frequency.

When the source moves away from the listener, the wavelengths are longer and the observed frequency is lower leading to lower pitched sound .

Question 20

What is the equation for a wavelength of an approaching source ?

Answer 20

λ = V - Vsource / Fsource

Question 21

What is the equation for the wavelength of a RECEDING source?

Answer 21

λ = V + Vsource / Fsource