Young

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• Youngs Double Slit
• Contents
• Interference
• Diffraction
• Youngs Double Slit
• Angle
• Distance
• Single slit
• Rayleigh Criterion

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Interference
Sources
L1
L2
When the difference in distance (L1- L2) is an
integer number of wavelengths (0, 1, 2, 3)
Constructive remainder of a half (1/2, 1 1/2, 2
1/2, ) Destructive
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Youngs Double Slit Experiment
Monochromatic, coherent light Light spreads out
from slits Screen has sum of two
sources Interference pattern on screen Demo
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Youngs Double Slit Experiment
L1
Next Maxima
d
Central Maxima
L2
d slit separation
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Youngs Double Slit Experiment
L1
Next Maxima
?
d
Central Maxima
L2
d slit separation d sin? n? (n 0, 1, 2) -
constructive d sin? (n 1/2)? - destructive
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Youngs Double Slit - Angle 1 2 3 4
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Two slits are 3.00 x 10-6 m apart. What is the
wavelength of the incident light if the bright
fringes are separated by 6.00o?
d sin? n? d 3.00 x 10-6 m, n 1, ? 6.00o
W
314 nm
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Two slits are 9.00 x 10-6 m apart. If 565 nm
light is incident, what angle separates the
central maxima, and the third fringe out?
d sin? n? d 9.00 x 10-6 m, n 3, ? 565 x
10-9 m
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10.9o
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Youngs Double Slit Experiment
L1
Next Maxima
d
Central Maxima
Similar triangles - set up proportion s ? D
d
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Youngs Double Slit Distance 1 2 3 4
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520 nm light hits two slits separated by 2.5 x
10-5 m. What distance separates the bright
fringes on the screen that is 5.0 m distant? s
? D d
d 2.5 x 10-5 m, D 5.0 m, ? 520 x 10-9 m
W
.10 m
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Light hits two slits separated by 2.50 x 10-5 m.
If 5.70 cm separates the bright fringes on the
screen that is 5.00 m distant, what is the
wavelength of light being used? s ? D
d
d 2.50 x 10-5 m, D 5.00 m, d .0570 m
W
285 nm
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A single slit can make an interference pattern too
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Rayleigh Criterion ? 1.22? b ?
Angle of resolution (Rad) ? Wavelength (m) b
Diameter of circular opening (m) (Telescope
aperture) the bigger the aperture, the smaller
the angle you can resolve.
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Rayleigh Criterion 1 2
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What is the angular resolution of the 100 inch
(2.54 m) diameter telescope on the top of Mt
Wilson? (use 550 nm as the wavelength) (uh 550
nm 550 x 10-9 m)
? 1.22? b ? ?, ? 550 x 10-9 m, b
2.54 m ? 2.64173E-07
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2.6 x 10-7 radians
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What diameter telescope do you need to resolve
two stars that are separated by 1.8 x 1011 m, but
are 3.0 1017 m from us? (use 550 nm as the
wavelength) (AU, 32 LY) hint ? s/r (1.8 x
1011 m)/(3.0 1017 m)
? 1.22? b ? 6.00 x 10-7, ? 550 x
10-9 m, b ? b 1.12 m
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1.1 m