Young's double slit experiment about light

1. Young’s Double-Slit
Experiment
By: Nancy Manhas

2. Importance
First performed by Thomas Young,
the two slit experiment is key to understanding
light and in general the microscopic world
The reasoning was to determine whether light
was a wave or a particle
A source of light illuminates two narrow slits
These slits project an image on the further
screen

3. Light as a Particle
If light acted as a particle then where ever it
passed through, it would form the image of the
slit, with the brightest line in the middle – called
the central fringe.

4. Light as a Wave
If light acted as a wave then it would diffract as it
passed through the slits
This diffraction through the slits, will give way to
the opportunity for points on waves to meet crest
to crest or crest to trough. Where crest to crest is
constructive, and crest to trough is destructive.
Constructive waves are light bands
Destructive waves are dark bands

5. During Young’s experiment it was noticed that
once light passed through the slits it would hit the
screen with different densities. Each density, has
a wavelength that correlates with a certain color
on the spectrum. This diffraction is the light
interfering with the wave, and adds more insight
to the wave-particle duality.
However, one needs to note that not only was
Young’s experiment a great contributor to
science, it was also a great contributor to the
idea that the observer’s eyes do not always
reflect what is actually happening.

6. Calculations
A pair of screens are 14.5m apart. A third order
fringe is seen on the screen 3.00cm from the
central fringe. If the slits were cut were 0.0960cm
apart, determine the wavelength of this light.

7. Need to understand that fringes are the bright lines
at which constructive interference intervenes. The
central fringe is the brightest band, with the highest
density of photons. The surrounding bands are
numbered by n.
Therefore, to determine we need to use a
mathematical formula based off the Fraunhofer
condition, where the distance between slit one and
two are compared to fringe of interest.
Simply use the following equation:
Lambda = distance from central fringe * distance
between slits/length from slits to screen * order of
fringe

8. Simply plug in the numbers:
Lambda = (0.03m)(0.000960m)/3(14.5m)
Lambda = 6.62 * 10-7m = 662 *10-9m = 662nm.
The wavelength is 662 nm long, which could be found
in the range of red.