3.Waves- Key Points

Question 1

The process of a stationary wave being formed on a string that is fixed at both ends

Answer 1

1. A wave is generated at one end of the string and travels down it
2. At the other end the wave is reflected and travels back in the opposite direction
3. The frequency of a wave generated and the length of the string are such that the next wave generated meets this wave and undergoes supersition
4. At places where the 2 waves are in phase they undergo constructive interference and form a maximum point known as an antinode
5. At places where the 2 waves are in antiphase they undergo destructive interference and form a minimum point known as a node

Question 2

The fundamental frequency of a wave on a string can be calculated by what equation?

Answer 2

f = 1/2L (T/µ)½
µ = M/L
T= mg

Question 3

What is Young’s double slit experiment

Answer 3

When two double slit are illuminated the two slots a few as coherent wave sources. Coherence means the waves have the same frequency with constant phase difference. The light diffraction at the slits and the two waves superpose , forming an interface pattern. This is because a combination of constructive and destructive interference occurs

Question 4

What’s the Double slit formula

Answer 4

W= λD/s 
λ = wavelength 
D = distance from screen 
W = fringe spacing 
s = distance between slits

Question 5

What happens in diffraction of the gap is a lot bigger than the wavelength

Answer 5

Diffraction is unnoticeable

Question 6

What happens in diffraction if the gap is a bit wider that the wavelength?

Answer 6

Diffraction is noticeable

Question 7

What happens in diffraction if the gap is the same size as the wavelength?

Answer 7

The diffraction is most noticeable

Question 8

What happens in diffraction if the gap is smaller than the wavelength?

Answer 8

Most waves are reflected

Question 9

What happens when monochromatic light is shone through a diffraction grating?

Answer 9

It displays a diffraction pattern

Question 10

What happens when white light is shone through a diffraction grating?

Answer 10

It creates a spectra of colours

Question 11

Name 3 uses of optical fibres

Answer 11

1. High-speed Internet cables
2. Medical imaging as endoscopes
3. Engineering inspections to view hard to reach areas

Question 12

What are the 2 main parts step-index fibres are made of?

Answer 12

1) A core made of a high refractive index material

2) Cladding made from a low refractive index material

Question 13

What are 3 purposes of cladding ?

Answer 13

1) Provides tensile strength to the optical fibre so it doesn’t break when twisted
2) Prevents information from being transferred between different cores in a bundle
3) Prevents core from being damaged

Question 14

Why must scratches on the core be prevented?

Answer 14

1) Water may get into the scratches which could make the refractive index higher than the core causing total internal reflection to not happen , causing the signal to exit the core
2) It may alter the angle light interacts with the boundary in such a way that the angle is lowered bellow the critical angle again causing total internal reflection to stop

Question 15

What is absorption ?

Answer 15

It is a loss in energy when a signal is transferred across a fibre , this results in a lower amplitude but doesn’t effect the frequency

Question 16

What can reduce absorption?

Answer 16

An optical fibre repeater which will boost the signal at periodic points along the fibre