Waves

Question 1

Which direction do the particles oscillate in a longitudinal wave?

Answer 1

In the same direction as the energy transferred, they oscillate around a fixed point

Question 2

Which direction do the particles oscillate in a transverse wave?

Answer 2

At 90 degrees to the direction of energy transfer

Question 3

What is the equation to work out time period?

Answer 3

1/f

Question 4

What is 1 wave cycle?

Answer 4

360 degrees

Question 5

What is phase difference?

Answer 5

the difference in the position or progress of two waves at a given time

Question 6

What is an example of a longitudinal wave?

Answer 6

Sound

Question 7

What are examples of a transverse wave?

Answer 7

The electromagnetic spectrum
water ripples

Question 8

How do you work out the speed of a wave?

Answer 8

C=fλ

Question 9

What is the speed of light?

Answer 9

3.00x10^8m/s

Question 10

What waves can be polarised?

Answer 10

Transverse waves

Question 11

What happens when light is polarised?

Answer 11

The electric field vibrates in only one direction (plane)

Question 12

What is polarisation useful for?

Answer 12

Transmitting via radio waves e.g. antennas
Sunglasses

Question 13

What is a node?

Answer 13

A position where there is no displacement

Question 14

What is an antinode?

Answer 14

A point of maximum displacement

Question 15

What is interference?

Answer 15

When one wave interferes with another

Question 16

What is superposition?

Answer 16

When you add 2 displacements of a wave together to get the final displacement

Question 17

What happens when you have a wave which is half a wave cycle out of phase with another one?

Answer 17

They cancel each other out

Question 18

What happens when you have a stationary wave?

Answer 18

The wave travels in one direction, bounces off the end and then interferes with itself
The two waves which are combining are coherent

Question 19

What is coherence?

Answer 19

When 2 waves have the same phase difference, similar amplitude and same wavelength and frequency

Question 20

When do we get constructive interference?

Answer 20

When the path difference is 0 or a multiple of a wavelength nλ

Question 21

When do you get maximum destructive interference?

Answer 21

Where waves are half a wavelength out of the other one (n+1/2)λ

Question 22

How do you work out frequency in a string?

Answer 22

1/2lx√T/μ
T=tension
μ=mass per unit length

Question 23

What is an experiment for measuring microwaves?

Answer 23

Have transmitter, opposite metallic plate so as wave comes out, reflects and goes back again
Put in microwave detector, as moves back and forth we can look at size of detected signal, 0 at end, maximum in middle where antinode is

Question 24

How can we measure waves with a tube?

Answer 24

Speaker on one end, tube with dust and plunger at one end which can be moved back and forth
When length is just right, particles form piles
Sound wave moves along and reflects off the end and interferes with itself
Also use Ruben’s tube with fire leaking at the top

Question 25

What are properties that waves have?

Question 26

What happens to sound when the interference is constructive?

Answer 26

It becomes louder

Question 27

What happens to sound when the interference is destructive?

Answer 27

Peaks and troughs cancel out so sound becomes quieter

Question 28

How do you carry out Young's double slit experiment?

Answer 28

Shine laser (monochromatic) light through double slit Laser light was similar wavelength to gap, so maximum diffraction through gap Shine onto screen and get diffraction patten of fringes of light(alternating maxima and minima) Measure width of fringes W, distance from screen D, distance between slits S W=λD/S

Question 29

How do you get wider fringes?

Answer 29

Put screen further away Use longer wavelength of light Decrease slit separation

Question 30

Why do we get light and dark fringes?

Answer 30

Points of constructive interference - light Points of destructive interference - dark

Question 31

What happens when you diffraction from a single slit?

Answer 31

Bright central maxima, dark point of destructive interference, duller and narrower bands either side

Question 32

What happens when you shine white light through single slit?

Answer 32

Bright white central maxima Destructive interference either side thendifferent wavelengths of light diffracted and spread out, rainbows Shorter to longer wavelength

Question 33

What happens when you shine laser light through a diffraction grating?

Answer 33

Central maxima Large region of no constructive interference Repeating bright spots then other regions

Question 34

What equation links distance between slits in diffraction gratings, order, wavelength and angle?

Answer 34

dsinθ=nλ

Question 35

When do you get maximum constructive interference?

Answer 35

When path difference = λ

Question 36

What is refraction?

Answer 36

When a wave slows down or speeds up and changes direction when passing from 1 medium into another

Question 37

What is Snell's law?

Answer 37

n1Sinθ1=n2sinθ2

Question 38

What is the equation to work out the refractive index of a material?

Answer 38

n=C/Cs Speed of light in a vacuum/speed of light in that material

Question 39

Equation when light goes from denser material to less dense material

Answer 39

n1sinθc=n2 Sinθc=n2/n1 To work out critical angle, look at ratios of refractive index of n2 and n1

Question 40

When do you get total internal refraction (TIR)?

Answer 40

When the angle hitting the boundary (angle of incidence) is bigger than the critical angle, so no light escapes and instead is internally reflected

Question 41

How do we make sure light is totally internally reflected in an optical fibre?

Answer 41

Add cladding on outside Step index

Question 42

What are problems with optical fibres and solutions?

Answer 42

Some of light is absorbed, signal at other end is a bit lower Have booster station to boost signal back up to original value so data can be transmitted over long distances Pulse broadening, signal at other end is shorter and wider due to modal and material dispersion Use other optical fibres to focus as much of the beam down the centre as possible

Question 43

What is material dispersion?

Answer 43

Some frequencies of light travel quicker than others so some parts arrive before others

Question 44

What is modal dispersion?

Answer 44

Some of the signal may be travelling in straighter lines, signals arrive at different times as they take different paths