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AQA A-Level Physics > Waves > Flashcards

Waves Flashcards

1
Q

Amplitude

A

Maximum displacement from the equilibrium.

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2
Q

Frequency

A

The number of complete oscillations passing through a point per second.

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3
Q

Wavelength

A

The length of one whole oscillation (e.g. the distance between successive
peaks/troughs).

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4
Q

Phase

A

The position of a certain point on a wave cycle, (units are radians, degrees or
fractions of a cycle).

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5
Q

Phase
difference

A

How much a particle/wave lags behind another particle/wave, (units are
radians, degrees or fractions of a cycle).

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6
Q

Period

A

Time taken for one full oscillation.

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7
Q

What is a progressive wave?

A

A wave made up of oscillating particles, transfers energy without transferring materials.

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8
Q

In phase

A

Whole number of wavelengths, e.g. nλ

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9
Q

Out of phase

A

Whole number + a half wavelengths (n+1/2)λ

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10
Q

What is the difference between longitudinal and transverse waves?

A

Transverse waves have oscillations perpendicular to the direction of energy transfer, while longitudinal waves have oscillations parallel to the direction of energy transfer.

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11
Q

What is a polarised wave?

A

A wave that oscillates in only one plane (only transverse waves can be polarised as polarisation can only occur if a wave’s oscillations are perpendicular to the direction of energy transfer).

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12
Q

What are the applications of polarisation?

A

Polaroid sunglasses, TV and radio signals.

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13
Q

What is superposition?

A

Displacements combined as they pass.

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14
Q

What is a stationary/standing wave?

A

Superposition of 2 progressive waves travelling in opposite directions in the same plane. Same wavelength, amplitude and frequency. No energy is transferred.

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15
Q

What are nodes?

A

Areas of no displacement, where the waves meet out of phase and destructive interference occurs.

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16
Q

What are anti-nodes?

A

Areas of maximum displacement, where waves arrive in phase, and constructive interference occurs.

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17
Q

What is the first harmonic?

A

Lowest frequency at which a stationary wave forms.

18
Q

How do you find the frequency of higher harmonics?

A

Frequency of the first harmonic multiplied by the harmonic number. (e.g. f, 2f, 3f…)

19
Q

What is the path difference?

A

Difference in distance travelled by 2 waves.

20
Q

Coherent

A

Same frequency, wavelength, and a fixed phase difference.

21
Q

Monochromatic

A

Emits light of a single wavelength.

22
Q

Why must the slits be the same size as the wavelength of the light in Young’s double slit experiment?

A

Light diffracts the most. When the gap is smaller, most waves are reflected, and when the gap is larger, there is less noticeable diffraction.

23
Q

Why is a single slit places before the double slit in Young’s double slit experiment?

A

Light must be coherent. By placing the single slit before, the light has a fixed path difference.

24
Q

What can we use to make light monochromatic?

A

A filter.

25
Q

What precautions must we take when using lasers?

A

Display a warning sign, wear laser safety goggles, do not shine the laser at anyone or at any reflective surfaces.

26
Q

What pattern is seen in Young’s double slit experiment?

A

A pattern of alternating light and dark fringes.

27
Q

What happens when sound waves interfere?

A

Rhythmic change in amplitude, loud to soft. The frequency of the new wave is the difference between the original two waves.

28
Q

Which waves diffract more?

A

Waves with longer wavelengths and lower frequencies. Waves with shorter wavelengths and higher frequencies diffract less.

29
Q

Stationary waves in an open tube

A

Node at the bottom, anti-node at the top.

30
Q

What is diffraction?

A

The spreading out of waves when they pass through or around a gap.

31
Q

What is the single slit diffraction pattern for monochromatic light?

A

Bright central fringe with alternating light and dark fringes either side (smaller).

32
Q

What is the single slit diffraction pattern for white light?

A

The different wavelengths of light are diffracted by different amounts - spectrum of colour. White central maximum, either side spectrum of colours, violet closest, red furthest.

33
Q

What happens when the slit width increases?

A

Diffraction decreases, central maximum becomes narrower and intensity increases.

34
Q

What happens when the wavelength increases?

A

Diffraction increases, central maximum becomes wider and intensity decreases.

35
Q

What is a diffraction grating?

A

A slide containing equally spaced slits very close together.

36
Q

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

A

When monochromatic light is passed through, the pattern is sharper and brighter.

37
Q

The more slits there are…

A

…the more the pattern is reinforced, it is therefore sharper and brighter.

38
Q

What is the refractive index?

A

Measures how much a material slows down light passing through it.

39
Q

What happens when the angle of refraction = 90 degrees?

A

The light is refracted along the boundary. At this point, the angle of incidence is the critical angle.

40
Q

When does total internal reflection occur?

A

When the angle of incidence is greater than the critical angle, therefore the refracted ray is reflected back, angle of refraction > 90 degrees. Material 1’s refractive index must be greater than material 2’s refractive index.

41
Q

Application of TIR: Optic fibres

A

Optic fibres are thin, flexible tubes of plastic or glass that carry information in the form of light signals. It has an optically dense core (high refractive index) surrounded by cladding with a lower optical density (lower refractive index) so TIR can occur. Cladding protects the core from damage and prevents signal degradation.

42
Q

What is signal degradation?

A

Losing information in the form of signals.

AQA A-Level Physics (9 decks)

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