Measuring the Wavelength of Light Using Young's Experiment

The light shows dual nature.

It shows the particle nature as well as the wave nature.

First of all. Huygens thought that light was a wave but, Isaac Newton did not.

But, Huygens was unable to prove the wave nature of the light.

The acceptance of the wave nature of light came many years later.

When in $1801$, Thomas Young did his classic double-slit experiment.

So, now, we will discuss measuring the wavelength of light using Young's experiment.

Let's measure the wavelength of light using Young's experiment.

Young first passed light from a single source through a slit.

He passed light through a slit to make it coherent light.

After that, Young did pass the light through the double slit.

Because, two slits will provide two coherent sources that will interfere further.

In Young's double-slit experiment, we use monochromatic light to clarify the effects.

And it shows the constructive and destructive interference of two waves.

The constructive interference occurs when two waves are in phase.

The destructive interference occurs when two waves are exactly out of phase.

Lightwave is diffracted into the semicircular waves after passing through the narrow slits.

It shows the bright fringe for constructive interference.

And it shows the dark fringe for destructive interference.

Now, let $\theta$ be the angle between the path and a line of slits. $d$ be the distance between slits.

So, from the trigonometry rules, the difference between the paths will be $dsin\theta$.

And for the constructive interference, the path difference must be an integral multiple of the wavelength.

Similarly, for the destructive interference, the path difference must be an half-integral multiple of the wavelength.

Now, we assume the distance from slits to the screen is much larger than the distance between slits.

So, the path from each slit to a common point on the screen will be differ by an amount of $dsin\theta$.

And for the double-slit interference, a series of bright and dark lines are formed.

For closer the slits, more bright fringes are spreading out.

And the wavelength of light can be found by,

This is all about measuring the wavelength of light using Young's experiment.

Revision

Young did pass the light through the double-slit to get the interference of waves.

The constructive interference occurs when two waves are in phase.

The destructive interference occurs when two waves are exactly out of phase.

The wavelength of light can be found by,

The End