Download Youngs Double Slit

4.1 Young's Double Slit Experiment
Equipment
Optical
Bench
Double
slit slide
Optical
Mounts
White
light
source
LED light sources
Adjustable
slit
Telescope
Activity
The double slit slide has several sets of slits. Use black tape to leave one set
of slits only. Set up the white light or white LED source on the optical bench.
Bring the slit up close to the eye and view the light source.
What do you see?
The interference pattern can only occur when the light diffracted by the two
slits is coherent or in phase with each other. Coherence can be achieved with
a laser, however Thomas Young performed this experiment in 1801 and did
not have access to such a device.
Instead Young used the arrangement shown in Figure 4.1 in which single and
double slits are employed to produce two coherent light sources. The light
forms a spectrum from each slit and constructive or destructive interference
occurs depending on the phase difference of the two paths for the light.
Figure 4.1 Young's double slit experiment
Acton Instruments - ANU
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4/30/2017
Young's experiment provided strong evidence for the wave nature of light and
the measurement of wavelength. The formation of spectra and interference
effects are exploited in the design and use of diffraction gratings.
The interference patterns or fringes can be investigated in more detail using a
single slit in front of the light source and the telescope to view the fringes
produced by the double slit. Refer to figure 4.2
telescope
double
slit
single
slit
LED
Figure 4.2 Observing double slit interference fringes
The single slit fits into one of the magnetic holders horizontally or vertically
and can be held open using the screws. Try different double slits but block out
the remainder.
Adjust the components and alignment to produce the best fringe pattern
possible.
Use the different coloured LEDs. Sketch the fringe patterns and note any
differences.
Explain the interference patterns and results in terms of the wave like nature
of light.
How are the colours and separation of fringes related to the wavelength of the
light?
Acton Instruments - ANU
Page 2
4/30/2017