- 1/T The number of oscillations per unit time

Waves 1 Flashcards by selin akhtar

Transverse wave:

Oscillations are perpendicular to the direction of energy transfer

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Longitudinal wave

Oscillations are parallel to the direction of energy transfer

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Amplitude

The maximum displacement from equilibrium

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Frequency

1/T
The number of oscillations per unit time

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Wavelength

λ = minimum distance between neighbouring identical points on the wave

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Time period

Time for one complete oscillation

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Displacement of a particle

The distance of a particle on a wave from the equilibrium position

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Phase Difference

Difference in radians between two points on the same wave or difference in radians between similar points on two waves

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Define the wave equation

v = f 𝛌
v = wave speed (ms^-1)
f = frequency (Hz)
𝛌 = wavelength (m)

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Define Intensity

Intensity is equal to the power per unit area (perpendicular to the direction of energy transfer)
I=P/A

If we are determining intensity from a sphere we use I=P/4pir^2 where 4pir^2 is the surface area of the sphere.

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What is the relationship between intensity and the distance r from the source

I ∝ 1/r^2
Intensity of a source is inversely proportional to the distance from the source squared.
For two scenarios, we can state :
I¹/I ₂ = r^2 ₂/r^2 ¹

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How are amplitude and intensity related?

I∝A^2
Therefore using ratios, for two scenarios 1&2 we can state
I1/I2 = A^2 ¹/A^2 ₂

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Give the range of wavelengths for visible light, a property, and a use:

Wavelength: 4x10^-7 - 7x10^-7
Property: Non-ionising and absorbed by matter causing some heating
Use: Human sight or optical fibres

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Give three examples of transverse waves:

Water waves
Electromagnetic waves
Seismic S-waves

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Under what circumstances are diffraction effects most significant?

When the size of the gap is about the same as the wavelength of the wave (then the wave spreads out the most)

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Give a more useful form of Snell’s law nsintheta=constant

n1sintheta1 = n2sintheta2

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Give the order of the electromagnetic spectrum from lowest to highest frequency:

Radiowaves
Microwaves
Infrared
Visible light
Ultraviolet
X-rays
Gamma rays

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What is the approximate refractive index of air?

Give the quantities and their units for the equation
nsintheta = constant

n = refractive index
theta = angle of incidence or refraction

What is meant by the term ‘plane polarised waves’?

Oscillations of a transverse wave are restricted to a single plane (longitudinal waves cannot be polarised)

What is a progressive wave?

A wave that transfers energy without transferring matter

Give the quantities and their units for the equation sinC = 1/n

sin C = critical angle
n = refractive index

Give two examples of longitudinal waves:

Sound waves (including ultrasound and infrasound)
Seismic P-waves

What is observed when an unpolarised light source is viewed through a fixed and a rotating polarising filter?

When transmission axis of filters align intensity is maximum, intensity decreases during rotation and is minimum when filters are at angle of 90degrees (then intensity begins to increase again)

Give the band of wavelengths for infrared radiation, a property, and a use:

Wavelength: 7x10^-7 - 10^-3 m Property: Non-ionising and mostly absorbed by matter causing heating Use: Night vision cameras, remote controls or optical fibres

Give the band of wavelengths for infrared radiation, a property, and a use:

Wavelength: 10^-16 - 10^-10 m Property: Ionising and mostly pass through matter Use: Medical tracers, radiotherapy, sterilisation or irradiation of food

Give the band of wavelengths for microwaves radiation, a property, and a use:

Wavelength: 10^-3 - 10^-1 m Property: Non-ionising and mostly pass through matter but cause some heating Use: Communication, Cooking or Radar

Define intensity of a progressive wave:

Radiant power passing through a surface per unit are (measured in Wm^-2)

Compare transverse and longitudinal waves:

In transverse waves oscillations are perpendicular to the direction of energy transfer and they have peaks and troughs, in longitudinal waves oscillations are parallel to the direction of energy transfer and they have compressions and rarefactions.

What is diffraction?

The spreading out of waves when they pass through a gap or around an obstacle (speed, wavelength and frequency DO NOT change)

Under what conditions will total internal reflection occur?

When light moves into a material with a lower refractive index, and for an angle of incidence above the critical angle

What is meant by the term 'critical angle'?

The angle of incidence for which the angle of refraction would be 90degrees, so light gets refracted along the boundary. Above the critical angle total internal reflection occurs

Give the quantities and their units for the equation n=cv

n = refractive index c = speed of light in a vacuum v = wave speed in the material

Explain how the path of a light ray changes when it enters a different medium:

-> If light goes to a more optically dense medium, light slows down and bends towards the normal. -> If light goes to a less optically dense medium, light speeds up and bends away from the normal. IN BOTH SCENARIOS ONLY THE WAVESPEED AND WAVELENGTH CHANGE THE FREQUENCY OF THE WAVE DOES NOT CHANGE!

Give the band of wavelengths for radio waves, a property, and a use

Wavelength: 10^-1 - 10^6 m Property: Non-ionising and passes through matter Use: Communication

Derive the wave equation:

Wave speed = wavelength/time period v=λ/T T=1/f Joining them together: v=λ/(1/f) v=fλ

Give an expression for the intensity of radiation a distance r from a point source of power P (radiating uniformly)

I = P/4pir^2

State the law of reflection

Angle of reflection is equal to the angle of incidence

Define the hertz

One hertz is one complete cycle per second (1Hz = 1s^-1)

What does an oscilloscope trace show?

Variation of voltage (y-axis) with time (horizontal axis)

Give the band of wavelengths for ultraviolet, a property, and a use:

Wavelength: 10^-8 - 4x10^-7 Property: Slightly ionising and absorbed by matter Uses: Sunbeds, security marks

Give at least three similarities between all electromagnetic waves:

-> Transverse Waves -> Propagate through oscillating electric and magnetic fields -> Speed of light in a vacuum -> Do not need a medium to propagate -> Can be polarised -> Can reflect -> Can refract

Give the range of wavelengths for x-rays, a property, and a use:

Wavelength: 10^-13 - 10^-8 m Property: Ionising and mostly pass through matter Uses: Medical imaging, radiotherapy or airport scanners