Harmonics / Interferance

Question 1

How do noises cancelling head phones work

Answer 1

Microphone on outside which detects so waves coming towards the ear.
They then transmit waves which are equal in amplitude and frequency but completely out of phase.
Two waves cause destructive interference and so waves cancel out.

Question 2

Superposed waves

Answer 2

When two waves meet they superpose and the resultant wave is equal to the sum of the two progressive waves.

Question 3

Principle of superposition

Answer 3

When two waves meet at a point the resultant displacement is equal to the sum of the displacement of the individual waves.

Displacement is a vector so resultant displacement could be bigger or smaller than indidiuval displacements

Question 4

Constructive interference

Answer 4

If two waves are in phase, max positive displacements line up. Resultant waves increase in amplitude .
Intensity is amplitude squared so intensity increases.

Question 5

Destructive interference

Answer 5

If two waves in antiphase, max pos displacement of one wave lines up with max neg displacement of the other one. Resulatant displacement twill be smaller. If amplitudes are equal then resultant displacement is zero.

Question 6

Phase difference

Answer 6

The difference between the displacements of particles along a wave or between particles in different waves

Question 7

Phase is measured in

Answer 7

Degrees or radians

Question 8

One complete cycle is

Answer 8

360° or 2pi radians

Question 9

Antiphase

Answer 9

Completely out of phase (180/pi radians)

Question 10

Stationary waves

Answer 10

When two progressive waves travelling in opposite directions superpose
Oscillating but not progressing
No net energy transfer

Question 11

When do stationary waves occur

Answer 11

Must have same frequency
Preferably same amplitude

Question 12

If waves also have a constant phase relationship

Answer 12

Resulatnat wave will have a pattern which does not move along the wave

Question 13

Same frequency and constant phase relationship

Answer 13

Coherent

Question 14

Node

Answer 14

Waves in antiphase
Displacement always 0
Amplitude =0
Intensity =0

Question 15

Antinode

Answer 15

Waves in phase
Greatest amplitude
Greatest intensity

Question 16

Waves travelling in opposite directions

Answer 16

No net energy transfer

Question 17

Particles between 2 nodes

Answer 17

All in phase
Move same direction
Amptitudes different
Partcles in middle move faster (further to go in same time )

Question 18

Particles on opposite sides of a node

Answer 18

Particles in antiphase
One side reaches max pos displacement at the same time other side reachers max neg displacement

Question 19

Fundamental mode of vibration depends on

Answer 19

Mass of string (thickness)
Tension of string
Length of string g

Question 20

Harmonics

Answer 20

Have diff wavelengths
Interfer with each other to produce sounds of instruments

Question 21

Harmonic number

Answer 21

Same number of antinodes

Question 22

Wavelength where L is length of string

Answer 22

Starts at 2/1 and denominator increases by 1 each time

Question 23

String wave speeds affected by

Answer 23

Tension of string ( newtons)
Mass per unit length of string (kg/m)

Question 24

f0=1/2L sqrt T/mew

Answer 24

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