Sound

Question 1

define wavelength

Answer 1

the distance travelled by a wave in one time period of vibration of the particle of the medium s

Question 2

speed of sound depends on

Answer 2

1. density (inverse)
2. temperature (direct)
3. humidity (direct)

Question 3

speed of sound not affected by

Answer 3

change in pressure

Question 4

how are electromagnetic waves formed

Answer 4

electromagnetic waves are formed by the periodic vibrations of the mutually perpendicular electric and magnetic fields in a plane normal to the direction of wave propagation
transfer energy as photons

Question 5

define reflection of a sound wave

Answer 5

the return of a sound wave on striking a surface such as wall, metal sheet, etc. back in the same medium

Question 6

requirement of reflection of sound wave

Answer 6

size of reflecting surface must be bigger than wavelength of sound wave

Question 7

define echo

Answer 7

the sound heard after reflection from a distant obstacle after the original sound has ceased

Question 8

condition for echo

Answer 8

1. minimum distance between source and reflector in air must be 17 m
2. size of reflector must be large enough as compared to wavelength of the sound wave
3. intensity of sound should be such that the reflected sound reaching the ear is sufficiently loud to be audible

Question 9

define reverberation

Answer 9

if there are repeated reflections at the reflected surface, the sound gets prolonged

Question 10

use of echo

Answer 10

sound ranging
echo depth sounding using ultrasonic waves

Question 11

properties of ultrasonic sound

Answer 11

1. travel undeviated through a long distance
2. can be confined to a narrow beam
3. not easily absorbed in a medium

Question 12

define natural vibrations

Answer 12

periodic vibrations of a body in the absence of any external force on it
the period of vibration depends on shape or size of the body

Question 13

why do natural vibrations only occur in vaccum

Answer 13

the presence of a medium around the sound wave offers some resistance to it, and hence the amplitude does not remain constant

Question 14

how is frequency related to length of air column

Answer 14

inversely related

Question 15

how is frequency related to radius of string

Answer 15

inverse

Question 16

how is tension related to frequency

Answer 16

direct

Question 17

nature of natural vibrations

Answer 17

simple, harmonic vibrations under the restoring force
amplitude and frequency remain constant

Question 18

define damped vibrations

Answer 18

the periodic vibrations of a body of decreasing amplitude in presence of a resistive force are called damped vibrations
rate at which energy is lost depends on nature of medium and shape and size of body

Question 19

how does frictional force related to velocity of the body

Answer 19

directly proportional at any instant

Question 20

define forced vibrations

Answer 20

the vibrations of a body which take place under the influence of an external periodic force acting on it

Question 21

body undergoing forced vibrations are acted upon what three forces

Answer 21

1. restoring force
2. frictional force
3. external periodic force / driving force

Question 22

amplitude of forced vibrations depend on

Answer 22

external periodic force

Question 23

how to keep amplitude of forced vibrations constant?

Answer 23

applying an external periodic force such that the driving force compensates for the loss of energy in each vibration due to the damped vibrations

these are called sympathetic vibrations

Question 24

amplitude at resonance depends on what

Answer 24

frictional forces

Question 25

define resonance

Answer 25

resonance is a special case of forced vibrations. when frequency of driving force on a body is equal to its natural frequency, body vibrates with increased amplitude

Question 26

characteristics of sound

Answer 26

1. loudness
2. pitch
3. quality/ timbre

Question 27

define loudness

Answer 27

characteristic by virtue of which a loud sound can be distinguished from a faint one, both having the same pitch and quality

Question 28

define intensity

Answer 28

the intensity of a sound wave at a point of the medium is the amount of sound energy passing per second normally through a unit area at that point

Question 29

unit of intensity

Answer 29

watt per metre^2

Question 30

intensity of ordinary sound and minimum sound

Answer 30

ordinary: 10^-6 W m^-2
minimum: 10^-12 W m^-2

Question 31

intensity of sound is proportional to

Answer 31

1. square of amplitude of vibrations
2. square of frequency of vibrations
3. density of air
4. velocity of sound in air

Question 32

loudness depends on

Answer 32

1. intensity
2. sensitivity of listener
3. square of distance from source (inverse)
4. amplitude (direct)
5. surface area (direct)
6. density of medium (direct)
7. presence of resonant bodies (direct)

Question 33

define noise pollution

Answer 33

disturbance produced in the environment due to the undesirable loud and harsh sound, of level above 120 dB from various sources such as loudspeaker, siren, moving vehicles, etc

Question 34

define pitch

Answer 34

that characteristic of sound by which a shrill note can be distinguished from a grave note of the same loudness and quality

Question 35

define quality of a sound

Answer 35

that characteristic which distinguishes the two sounds of the same loudness and same pitch, but emitted by two different instruments because of change in their wave forms

Question 36

quality depends on

Answer 36

wave form

Question 37

define principal/ fundamental vibration

Answer 37

the vibration of the lowest frequency and maximum amplitude

Question 38

define subsidiary/secondary vibrations

Answer 38

vibrations of frequency integer multiples of principal vibrations. small amplitudes.

Question 39

define music

Answer 39

it is a pleasant, continuous and uniform sound produced by regular and periodic vibrations

Question 40

define noise

Answer 40

the sound produced by an irregular succession of disturbances