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P5- OPTICS > 5.5- MORE ABOUT INTERFERENCE > Flashcards

5.5- MORE ABOUT INTERFERENCE Flashcards

1
Q

Why are double slits described as coherent sources?

A

they emit light waves of same frequency with constant phase difference, provided we illuminate double slit with laser light, or with light from narrow single slit if we’re using non-laser light

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2
Q

How does each wave crest or wave trough from the single slit always pass through one of the double slits?

A

a fixed time after it passes through the other slit

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3
Q

As each wave crest or wave trough from the single slit always passes through one of the double slits a fixed time after it passes through the other slit, what does this show?

A

double slit emits wavefronts with constant phase difference

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4
Q

What does the straight waves from the beam vibrating on the water surface in the double slit arrangement do?

A

diffract after passing through two gaps in barrier + produce interference pattern where diffracted waves overlap

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5
Q

What happens if one gap is closer to the beam than the other in the double slit arrangement?

A

each wavefront from beam passes through nearer gap first

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6
Q

What is the same even if one of the gaps is closer to the beam in the double slit arrangement?

A

time interval between same wavefront passing through the two gaps always same so waves emerge from gaps with constant phase difference

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7
Q

Why can’t light from two nearby lamp bulbs not form an interference pattern?

A

as the two light sources emit light waves at random

points of cancellation + reinforcement would change at random, so no interference pattern possible

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8
Q

in the double slit experiment, what does the fringe separation depend on?

A

colour of light used

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9
Q

What is white light composed of?

A

continuous spectrum of colours, corresponding to continuous range of wavelengths from about 350nm for violet light to about 650nm for red light

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10
Q

Is fringe separation greater for red light or blue light?

A

red light

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11
Q

Why is fringe separation greater for red light than blue light?

A

red light has loner wavelength than blue light

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12
Q

formula for fringe spacing w

A

w = λD/s

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13
Q

What do vapour lamps and discharge tubes produce?

A

light with dominant colour

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14
Q

What glow does a sodium vapour lamp produce?

A

yellow/orange glow

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15
Q

Why does sodium vapour lamp produce a yellow/orange glow?

A

due to light of wavelength 590nm

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16
Q

Are other wavelengths of light also emitted from a sodium vapour lamp?

A

yes

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17
Q

If other wavelengths of light is emitted from a sodium vapour lamp, why is the colour yellow/organge?

A

colour due to light of wavelength 590nm much more intense

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18
Q

What sort of light source is a sodium vapour lamp?

A

monochromatic light source

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19
Q

How is a sodium vapour lamp a monochromatic light source?

A

its spectrum is dominated by light of a certain colour

20
Q

What is light from a filament lamp or from the Sun composed of?

A

colours of spectrum and so covers continuous range of wavelengths from about 350nm to about 650nm

21
Q

What happens if a beam of white light is directed at a coloured filter?

A

light from the filter is a particular colour

22
Q

Why is that when a beam of white light is directed at a coloured filter, light from the filter is a particular colour?

A

as it contains a much narrower range of wavelengths than white light does

23
Q

How does light from a laser differ from a non-laser light? (2)

A

laser light highly monochromatic

laser is convenient source of coherent light

24
Q

What does the wavelength of laser light depend on?

A

type of laser that produces it

25
Q

What light does a helium-neon laser produce?

A

red light of wavelength 635nm

26
Q

Why can a convex lens be used to focus a laser beam to a very fine spot?

A

as a laser beam is almost perfectly parallel + monochromatic

27
Q

What happens to the beam power when the beam light is focused to a very fine spot using a convex lens?

A

beam power concentrated in very small area

28
Q

Why is it dangerous if a laser beam enters the eye?

A

eye lens would focus beam on tiny spot on retina + intense concentration of light at that spot would destroy the retina

29
Q

Should you look along a laser beam, even after reflection?

A

no

30
Q

Why can we use a laser directly to illuminate the double slit when demonstrating double slit interference?

A

laser is source of coherent light

31
Q

What doesn’t need to be done in the double slit experiment when using a laser beam as it’s a coherent source of light?

A

don’t need to make light pass through narrow single slit

32
Q

What does a light source emit light as a result of?

A

electrons inside its atoms moving to lower energy levels inside atoms
each such electrons emits a photon

33
Q

What is a photon?

A

packet of EM waves of constant frequency

34
Q

What happens inside a laser, when a photon is emitted?

A

each photon causes more photons to be emitted as it passes through light-emitting substance

35
Q

As each photon causes more photons to be emitted as it passes through a light-emitting substance in a laser, what does this mean?

A

photons in laser beam are in phase with each other

36
Q

What type of light source is a laser?

A

coherent source of light

37
Q

How do atoms emit photons in a non-laser light source?

A

atoms emit photons at random so photons in such beam have random phase differences

38
Q

What are the blue light fringes like in comparison to red light fringes?

A

blue light fringes closer

39
Q

What does each component colour of white light produce?

A

its own fringe pattern

each pattern centred on screen at same position

40
Q

What colour is the central fringe of white light?

A

white

41
Q

Why is the central fringe of white light white?

A

as every colour contributes at centre of pattern

42
Q

What are the inner fringes tinged with on the inner side and outer side?

A

inner side tinged with blue and outer side tinged with red

43
Q

Why are the inner fringes tinged with blue on the inner side and red on the outer side? (white light fringes)

A

red fringes more spaced out than blue fringes and the two fringe patterns do not overlap exactly

44
Q

What do the outer fringes merge into? (white light fringes)

A

into an indistinct background of white light becoming fainter with increasing distance from centre

45
Q

Why do the outer fringes merge into an indistinct background of white light becoming fainter with increasing distance from the centre?

A

where fringes merge, different colours reinforce and so overlap

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