Section 3 - Waves and Optics Flashcards by ROWAN Gomanee

What are the two types of wave?

Transverse & Longitudinal

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True or false transverse waves can be polarised?

True

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True or false longitudinal waves can be polarised?

False

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What is the direction of energy transfer for a transverse wave?

Perpendicular to the direction of travel

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What is the direction of energy transfer for a longitudinal wave?

Parallel to the direction of travel

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Give two examples of a transverse wave

Examples include:
* Any EM wave
* S-wave

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Give two examples of a longitudinal wave

Examples include:
* Sound wave
* P-wave

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Features of a transverse wave?

Has troughs and peaks

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Features of a longitudinal wave?

Has compressions and rarefactions

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What does a transverse wave look like?

Looks like a sinusoidal wave

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What does a longitudinal wave look like?

Looks like a spring

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Where can we get unpolarised light from?

Sources include:
* The sun
* Flourecent lamps
* Fire

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Define plane polarisation

Wave particles oscillate in one plane

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How do we polarise a wave?

Using a polarising filter

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How much light does parallel polarisation let through?

All of the light passed through the filter

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How much light does perpendicular polarisation let through?

None of the light

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Define amplitude

Maximum displacement from the equilibrium position

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Define frequency

Number of complete wave cycles per second

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Define time period

The time taken for one wavelength to pass a specific point

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Define displacement

Distance from the equilibrium position

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Define wavelength

The distance between two points in phase

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What is the wave speed equation?

C = f. lambda

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Equation for finding the phase difference between two points?

(x % lambda) * 2pi

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When does a wave refelct?

When it hits a hard surface

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What is the reflection law?

The angle of reflection is equal to the angle of incidence

When does refraction occur?

When a wave enters a medium with a different optical density

Why does refraction occur?

The beam changes velocity, this causes the light to bend

What is diffraction?

Waves spread out after passing through a gap

What is superposition?

When two waves meet the total displacement is the sum

How are stationary waves formed?

* Progressive wave hits a hard surface; it reflects * reflected wave has similar amplitude, same frequency and wavelength * Two wavse superpose * they interfere constructively at points in phase - node formed * interfere destructively at points out of phase - anti-node formed

True or false the amplitude of a stationary wave is the same at all points?

False

Define refractive index

The ratio of the speed of light in a vacuum and the speed of light in substance

Does frequency change when entering a new medium?

No it does not

Does wavelength change when entering a new medium?

Yes

Do longer wavelengths get refracted the most or the least?

The least

Do shorter wavelengths get refracted the most or the least?

The most

When does TIR occur?

When the angle of incidence is greater than the critical angle

What condition must be met for TIR to occur?

n1 >n2

How does an optical fibre work?

* Light enters the fibre at varying angles * The lights undergoes TIR until it exits the fibre

What is the purpose of the cladding?

* To protect the core * To lower the critical angle * To prevent cross talk

What is modal dispersion?

* Light takes different paths to the end of the fibre. * This varies the time taken by different rays * As a result the light doesn't arrive all at once

How to fix modal dispersion?

Narrow the core

What is material dispersion?

* Differerent wavelengths of light causes the light to take different paths down the fibre. * This causes the light to take varying amounts of time to reach the end of the fibre

How to fix material dispersion?

Use monochromatic light

Examples of when optical fibres are used

Data transfer Medical endoscopes

Define coherent

Constant Phase relationship

Define monochromatic

A single wavelength

Why do maxima form on a screen when passed thorugh a double slit?

* The light source passed through the double slit forms two coherent wave sources * The two waves superpose * They interfere constructively at points in phase and form bright fringes * They interfere destructively at points out of phase and from dark fringes * At bright fringes the path difference is nλ * At dark fringes the path diffenrence is n/2 * λ

What is the approximate wavelength for red light?

650nm -700 nm

What is theapproximate wavelenght for violet light

350nm

What seen on the screen when white light is passed through a double slit?

* Bright white central maxima * Fringes are a full spectra * Fringes have a wider W * Blue light is closest to the central maxima

What is single slit diffraction?

* There are an infinite amount of wavelets coming through the slit * Wavelets at either end of the slits have a path difference by the thime they reach the screen * Talk about interference in the sam eway for double slit

What does the intensity graph look like for a single slit?

* Peak intensity of the fringe drop off very quickly * Central maxima is twice the width of the other fringes

What must the two wave sources do in order for diffraction to occur in a double slit?

They must overlap

How can we ensure that the two wave sources overlap?

* Making sure the slits are narrow enough to diffract the light sufficently * Making sure the slits are close enough so the light overlaps on the screen

Formula for wavelength in a single slit?

λ = W.s/2D

What is a diffraction grating?

A plate with closely placed parallel plates

What does a diffraction grating cause?

Concentrated maxima

What is the central beam often reffered to as?

The zero order beam

How to increase the angle of diffraction?

* Use light of a longer wavelength * Use a grating with closer slits

What is the diffraction grating equation?

nλ = d>sin(θ)

How do you find the biggest possible value of n and why?

* 1. Set θ to 90 the solve for n * Because this the greatest possible angle of diffraction

What colour of light has the lowest refractive index?

Red

What colour of light has the highest refractive index?

Blue

What is the equation for light intensity?

Why do different wavelengths of light have different refractive indices?

What kind of wave does not require a medium to propagate through?

Electromagnetic

What kind of wave consists of an oscillating electric field and a perpendicular oscillating magnetic field?

Electromagnetic

graph of displacement versus time for a wave applies to a particular ____?____ on the wave.

Particle

A graph of displacement versus distance for a wave shows the position of the particles at a particular ____?____.

time

Why do different wavelengths of light take different amounts of time to travel through an optical fibre?

Wavelength changes with different optical densities. Different colours of light refract by a different amount so they will reflect at different angles. Longer wavelengths will refract the least to their path will be shorter than shorter wave lengths of light.