A level Physics (6)

A Level Physics

6.1 Interference & Coherency
6.2 Young's Double Slits
6.3 Thin-film interference
6.4 Diffraction
6.5 Reflection & Refraction
6.6 Lens Systems
6.7 Optical Instruments

6.1 Interference & Coherency

Light from 2 separate sources is not coherent \ it doesn't produce steady interference patterns.
The production of light waves from electron transitions in excited atoms is random (short pulses) & \ not a continuous wave train. The phase relationship is not constant. In laser light the electron transitions are stimulated in phase with each other (continuous wave) \ lasers can be used as 2 separate coherent sources.

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6.2 Young's Double Slits ( examples )

_______ Young's double slits

Fringe Spacing Diagram:
_______ Young's double slits - fringe spacing
___sin q = sin(theta) = lambda/d ___q is small \tan q sin q,___tan q = ___ \ = ___

Experiment to determine the wavelength of light - Young's Slits:
___ experiment - Young's Slits ____ lambda

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6.3 Thin-film interference ( examples )

Air films - General interference conditions

constructive or destructive interference is determined from total phase difference between 2 reflected rays (overlapping). At any point the path difference = twice the thickness (t) of the film. ( l/2 phase change occurs when ray reflects off the lower glass surface ).

Constructive interference : ___2t + = nl
Destructive interference : ___2t + = ( n + )l

Air Wedge:
___ tan q = __(2t_n = nl) ^*1 __\ w =

Newton's Rings:
Newton's rings - lens & interference pattern
Ring Radius:
Newton's rings - calculating lens radius ___ *__(2R - t_n)t_n = r_n²___Þ 2Rt_n = r_n² ___(as 2t_n = nl) ^*1 __\ r_n² = 2R_nl .
__destructive interference: 2t_n = nl ^*1

Experiment using thin-film interference

i) Air Wedge:
_____ air wedge plates - diagram ^*2

ii) Thin film interference in transmitted light:

___________________ transmitted light - diagram
l/2 phase changes at A & B gives no net phase difference seen by observer (waves meet - constructive interference) ^*3

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6.4 Diffraction ( examples )

Single-slit Diffraction

$single-slit diffraction thr' lens$ $single-slit diffraction ~ // rays$

Experimental demonstration of single-slit diffraction

_ $Experiment - single-slit diffraction$

Calcuating position of minima

$Experiment - single-slit diffraction$

relative intensity vs. theta

________________ Huygen's principle & the formation of maxima

Derivation of grating formula for positions of angular maxima ______ Experimental measurement of wavelength of light using a grating spectrometer

Spectrometer____________________________________Grating Spectra

spectrometer measurements _______ grating spectra

line (monatomic gas element) & band (molecular gases) spectra

Emission spectra - line & band, electrical breakdown occurs in the gas at high p.d.
Continuous spectra - high density gases, visible light rainbow.
Absorption spectra - white light - gas or vapour, low density, passing through a tube.

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6.5 Reflection & Refraction ( examples )

reflection ____ $refraction$ ____ $refraction & medium$

Snell's Law

____ Snell's Law

critical angle total internal reflection general case

________________ Snell's law at critical angle

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6.6 Lens Systems ( examples )

lens systems - convex, concave

________________ lens formula

___ 2nd lens closer to 1st than 1st image ___ magnifiying glass or simple microscope
____________ magnification ____________ formulas for magnification

_ compound microscope formulas for magnification 2

_ astronomical telescope _____ telescope formulas

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6.7 Optical Instruments ( examples )

_ resolving power _____ $resolving power formula - diffraction theory$

______________________ Spectrometer

__________________________ example of lens problem

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Reference

1. If s = r then q = 1 radian ( rad ) - 1 rad is the angle subtended at the centre of a circle by an arc = in length to the radius. The circumference is s = 2pr where q = 2p rad. ( or 360° ).

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