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Interference QER
- Module
- PH2 - Waves & Particles
- Institution
- WJEC
Unit 2 a level physics notes
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double slit interferenceExplain conditions required of the light sources, for a
two source interference pattern to be observed.
For a two source interference pattern to be observed
the waves must be travelling in opposite directions with
'Game"bath difference of integer (na) number of wavelengths
apart.The 2 waves must be coherent and in phase. Interference
is the overlapping of waves. superposition Law must be
obeyed where the amplitude of the 2 waves added together
is equal to the Max displacement of the wave. Constructive
interference must occur where amplitude 1 + amplitude 2 of
each wave = a greater amplitude for the resultant wave.
PERFECTED ANSWER!
For a two source interference pattern to be observed constructive bright spots
the light source must meet following conditions.
The light source must be COHERENT meaning light has a 2
= 1+2
CONSTANT PHASE DIFFERENCE. Light source must emit amplitudes add up
light of the SAME FREQUENCY or WAVELENGTH. If waves
constructively interfere their AMPLITUDES add up. If waves deconstructive dark spots
destructively interfere their AMPLITUDES cancel out. For cancel out
CONSTRUCTIVE' INTERFERENCE fringes are bright and for 2
=
DESTRUCTIVE INTERFERENCE fringes are dark. Amplitude 1+2
of light waves indicates the interference pattern given out.
The two sources of light must emit waves that have the The amplitude indicates interference pattern!
same POLARISATION. No cancellation if polarization amplitudes 2 sources emit waves of same polarisation
or directions different. DIFFRACTION occurs as the sources
overlap creating the spreading out of the wave with use laser not lamp!
constructive + destructive interference. If two sources
of light travel at 90' to each other no light can
pass the screen or slit. Light waves must be either parallel
or perpendicular to each other to constructively or deconstructively
interfere. Requirements would be met if two slits illuminated
by a laser but not using a lamp.
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