4.1 Waves and vibrations

Question 1

What are waves?

Answer 1

» Vibrations which pass through a substance

Question 2

How are sound waves created?

Answer 2

» By making a surface vibrate so it sends compression waves through the surrounding air

Question 3

What are mechanical waves?

Answer 3

» Waves with pass through a substance

Question 4

What are electromagnetic waves made up of?

Answer 4

» Oscillating electric and magnetic fields that progress through space without the need for a substance

Question 5

How is the magnetic field made in an electromagnetic wave?

Answer 5

» The vibrating electric field generates the magnetic field
» Which generates a vibrating electric field

Question 6

What are some examples of electromagnetic waves?

Answer 6

» Radio waves
» Microwaves
» Radiation
» Light
» Gamma radiation

Question 7

What are longitudinal waves?

Answer 7

» Waves in which the oscillations are parellel to the direction of energy transfer

Question 8

What are 2 examples of longitudinal waves?

Answer 8

» Primary seismic waves
» Sound waves

Question 9

What are the 2 features of a longitiduinal wave?

Answer 9

» Compression
» Rarefaction

Question 10

What is the definition of compression?

Answer 10

» Is a region in a longitudinal wave where the particles are closest together

Question 11

What is the definition of rarefaction?

Answer 11

» Is a region in a longitudinal wave where the particles are furthest apart

Question 12

What are transverse waves?

Answer 12

» Waves in which the oscillations are perpendicular to the direction of energy travel

Question 13

What are 2 examples of transverse waves?

Answer 13

» Secondary seismic waves
» Electromagnetic waves

Question 14

What does it mean if waves can be plane-polarised?

Answer 14

» The polarised waves can be reduced to one plane of oscillation only

Question 15

What waves can be polarised?

Answer 15

» Transverse waves

Question 16

Why cannot longitudinal waves be polarised?

Answer 16

» Longtiudinal waves only have a single plane where oscillation happens
» Polarisation cannot happen as the oscillations do not change from one plane to another

Question 17

How does a slit cause polarisation?

Answer 17

» A slit causes polarisation as only certain oscillations can pass through the slit

Question 18

What happens if unpolarised light is passed through a polaroid filter?

Answer 18

» Transmitted light is polarised as the filter only allows through light which oscillates in a certain direction
» According to the alignment of its molecules

Question 19

How can the transmitted light intensity change?

Answer 19

» If one polaroid is turned relative to the other one

Question 20

What does it mean if the filters are crossed?

Answer 20

» Where the transmitted intensity is the minimum

Question 21

How can the polarised light not pass through any of the 2 filters when they are crossed?

Answer 21

» At this position the polarised light from the first filter cannot pass through the second filter, as it is at a right-angle to the alignment in the first filter

Question 22

What angle causes the minimum light intensity?

Answer 22

» 90 degrees

Question 23

How is the direction of polarisation defined as?

Answer 23

» The plane in which the electric field oscillates

Question 24

What is the purpose of Polaroid sunglasses?

Answer 24

» Reduces glare of the light reflected by water or glass

Question 25

What is the defintion of unpolarised?

Answer 25

» Wave vibrations occur in all planes perpendicular to the direction of travel

Question 26

How does a polarised sunglass reduce the glare of light reflected by water or glass?

Answer 26

» Reflected light is polarised
» Intensity is reduced when it passes through the polaroid sunglasses

Question 27

What happens when unpolarised light reflects of a non-metallic surface?

Answer 27

» It can be polarised
» Depends on the angle at which the light approaches

Question 28

What is the motion of the particle at an instance if it is at the amplitude?

Answer 28

» At rest

Question 29

Sketching a normal transverse wave, what is the motion of the particle at the amplitude in the next moment?

Answer 29

» Down

Question 30

How can you figure how the motion of the particle in the next moment?

Answer 30

» Draw another wave which is shifted to the right
» Draw an arrow to see whether its going up or down

Question 31

What is the best way to remember what waves transfer?

Answer 31

» Transfer energy not matter, so does not transfer the actual particle in the wave
» Transvere waves the movement is perpendicular
» So it will go up or down

Question 32

What is the general rule for predicting particle motion?

Answer 32

» It will always follow the direction of a particle that was before it

Question 33

What happens if the left neighbour is below the particle?

Answer 33

» It will follow and go down

Question 34

What happens if the left neighbour is above the particle?

Answer 34

» It will follow and go up

Question 35

How can polarisation be used to distinguish between transverse waves and longitudinal waves?

Answer 35

» Only transverse waves can be polarised
» Longitudinal is already restricted to one plane of oscillation, polarising it would remove the energy the wave carries

Question 36

What can be deduced if a seismic wave is polarisable?

Answer 36

» Must be transverse waves
» Therefore must be a secondary seismic wave

Question 37

Which direction does a point move if it is in the rarefaction, when it is moving?

Answer 37

» Moves to the left to the compression

Question 38

Which direction does a point move if it is in the compression, when it is moving?

Answer 38

» Moves to the right to the rarefaction

Question 39

What is the general rule for the motion of any particle?

Answer 39

» Oscillates about equilbrium position