View source for Apps-On-Physics/C3/Interference-and-Diffraction/English

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|-
|| '''Visual Cue '''
|| '''Narration'''

|-
|| '''Slide Number 1 '''

'''Title Slide'''
|| Welcome to the Spoken Tutorial on '''Interference and Diffraction'''.

|-
|| '''Slide Number 2 '''

'''Learning objective '''

|| At the end of this tutorial you will be able to,
* Verify the relation between wavelength and relative intensity.
* Find the relation between slit width, maxima and minima.
* Calculate the angle for the given maxima.
* Interpret diffraction intensity profile.
* Verify the relation between wavelength and angle.


|-
|| '''Slide Number 3'''

'''System Requirements'''
|| Here I am using,

Ubuntu Linux OS version 16.04

Firefox Web Browser version 62.0.3

|-
|| '''Slide Number 4'''

'''Pre-requisites'''

[https://spoken-tutorial.org/ https://spoken-tutorial.org/] '''
|| To follow this tutorial, 

learner should be familiar with '''Apps on Physics'''.

For the Pre-requisites tutorials please visit this site.

|-
|| Point to the file in the downloads folder
|| I have already downloaded '''Apps on Physics '''to my '''Downloads''' folder.

|-
|| '''Slide Number 5'''

'''Apps on Physics'''
|| In this tutorial we will use,

'''Interference of Light at a Double Slit''' 

and '''Diffraction of Light by a Single Slit Apps'''.

|-
|| Right click on''' doubleslit_en.htm''' file.

Select the '''Open With Firefox web Browser''' option.

Cursor on the '''App'''.
|| Right click on''' doubleslit_en.htm '''file.

Select the '''Open With Firefox web Browser '''option'''.'''

'''App''' opens in the browser.

|-
|| Point to the set-up.
|| The '''App''' shows '''Young’s double slit '''experiment for the interference pattern. 

|-
|| Point to the slit and semicircular black colour screen.
|| The setup includes a slit and a semicircular screen.

|-
|| Point to the '''Wavelength'''.
|| On the green panel we can change the wavelength of the source light.

|-
|| Cursor on the Wavelength slider.

Drag the '''Wavelength''' slider.
|| Here the range of the wavelength is from 380 nanometer to 780 nanometer. 

This is the range of visible spectrum.

|-
|| Enter value 650 nm and show.
|| We can also enter the value of wavelength in the text-box.

|-
|| Cursor on the interface.
|| Let us see how change in wavelength changes the interference pattern.

|-
|| Drag the '''Wavelength''' slider to 380 nm.
|| Drag the '''Wavelength''' slider to 380 nm.

|-
|| Click on '''Intensity profile''' radio button.
|| Click on '''Intensity profile''' radio button at the bottom of the green panel.

|-
|| Drag the '''Wavelength''' slider.

Point the cursor on the graph.
|| Drag the '''Wavelength''' slider slowly towards higher wavelength.

Observe the graph showing dark and bright fringes in the intensity profile.

|-
|| Cursor on the graph.
|| As the wavelength increases, distance between dark and bright fringes increases.


|-
|| Drag the '''Angle''' slider to show the changes.
||Next Drag the '''Angle''' slider here we can change the angle from 0 degrees to 90 degrees.

|-
|| Point the cursor to show the movement of white arrows 
|| Note that as we change the angle, white arrows shifts their position.

|-
|| Drag the '''Angle''' slider and point to show the shift in the graph.
|| This shift is also shown in the graph.

|-
|| Scroll down.
|| Scroll down the screen.

|-
|| Point to show the condition for maxima and minima
|| Here the conditions for maxima and minima are given.

For more details please read the additional material provided in this tutorial. 

|-
|| Press '''F5''' key on the keyboard to restart the '''App'''.
|| Press '''F5''' key on the keyboard to reset the '''App'''.

|-
|| Drag the slider of '''Spacing between the slit''' to 2000.
|| Scroll up and increase the spacing between the slit to 2000 nm.

|-
|| Click on the '''Maxima''' drop down.

Move the cursor to show all the values.
|| Now click on the '''Maxima '''drop down.

Here we will see more options for the '''k '''value.

|-
|| Click on the '''Minima '''drop down.
|| Click on the '''Minima''' drop down.

|-
|| Point to first minima(k=1).
|| Note that the first minima is formed at 8.6 degrees.

|-
|| Click on the second minima(k=2).
|| Click on the second minima that is''' k=2'''. 

|-
|| Point to show both screen and graph.
|| The white arrows shift to the second minima in both screen and graph.

|-
|| Point to show the '''Relative intensity'''. 
|| Here the '''Relative intensity''' changes to zero(0).

Zero indicates dark fringe.

The waves superimpose and are out of phase to give zero intensity.

This is destructive interference.

|-
|| Click on '''Intensity profile''' radio button.
|| Click on the '''Intensity profile''' radio button.

|-
|| Point to the red point on the intensity profile graph.
|| Here note that the red points indicate zero intensity.

|-
|| Click on''' Maxima''' drop down. Select '''k=3'''.
|| Now click on '''Maxima '''drop down and select '''k=3'''. 

|-
|| Point to the red point.

Point the cursor to '''Relative intensity'''.
|| The red point has shifted to the third peak.

The '''Relative intensity''' has changed to 1.

Here the waves superimpose to form a wave with maximum intensity.

This is constructive interference.

This constructive interference results in a bright fringe.

|-
|| Click on '''Interference pattern''' radio button.
|| Click on '''Interference pattern''' radio button at the bottom of the green panel.

|-
|| Cursor on the graph.
|| Note that the interference graph shows equally spaced dark and bright fringes.

Therefore the value of relative intensity only shows 0 and 1.

|-
|| Press''' F5 '''key on the keyboard.
|| Press '''F5''' key on the keyboard to reset the '''App'''.

|-
|| Cursor on the interface.
|| Let us calculate the value of angle for first maxima.

|-
|| Point to '''Condition for maxima''' formula.

Show the rearranged equation in the text-box.('''α <nowiki>= sin</nowiki><sup>-1</sup>(kλ/d)''').
|| To do so we can rearrange the equation given in the interface 

'''α <nowiki>= sin</nowiki><sup>-1</sup>(kλ/d)'''

|-
|| '''Slide Number 6'''

'''Angle'''

'''α <nowiki>= sin</nowiki><sup>-1</sup>(kλ/d)'''

'''k<nowiki>=1</nowiki>'''

'''λ<nowiki>= 600 nm</nowiki>'''

'''d = 1000 nm'''

'''α <nowiki>= sin</nowiki><sup>-1</sup>(kλ/d)'''

'''<nowiki>= sin</nowiki><sup>-1</sup>(1*600/1000)'''

'''<nowiki>= sin</nowiki><sup>-1</sup>(600/1000)'''

'''<nowiki>= sin</nowiki><sup>-1</sup>(3/5)'''

'''<nowiki>= 36.86</nowiki>°'''
|| Take the value of k as 1 since we have to calculate the angle for the first maxima.

Take the value of wavelength and spacing between slit as shown on interface.

Next substitute the values in the formula.

The calculated value of angle of first maxima is 

36.86 degree.

Let us compare with the value shown in the '''App'''.

|-
|| Click on '''Maxima''' drop down.

Select '''k=1'''.
|| Click on the''' Maxima''' drop down and select '''k=1'''.

|-
|| Cursor on the angle next to k=1.
|| Observe that the value of the angle next to K=1 is 36.9 degrees.

The value is comparable with the calculated value.

|-
|| '''Slide Number 7'''

'''Assignment'''

Change the Spacing between slits to 3500 nm.

Calculate the angle of fourth and fifth maxima.
|| As an Assignment 

Change the Spacing between slits to 3500 nm.

Calculate the angle of fourth and fifth maxima.

|-
|| 
|| Let us move on to the next '''App'''.

|-
|| Right click on '''singleslit_en.htm '''file and select the option '''Open with Firefox Web browser'''.

Cursor on the title.
|| Follow the same steps as shown earlier while opening the''' App.'''

The '''Diffraction of Light by a Single Slit '''opens on the screen.

|-
|| Cursor on the simulation interface.
|| This '''App''' shows the setup of diffraction through a single slit experiment.

This set up is also known as '''Fraunhofer's Diffraction at a single slit'''.

|-
|| Scroll down and point the cursor on the formulas.
|| scroll down to see the conditions for maxima and minima.

|-
|| Scroll up.

Select '''Intensity profile''' radio button.
|| Scroll up and select '''Intensity profile''' radio button.

|-
|| Point the cursor on the Intensity profile graph.
|| Observe that, only one central bright region is seen.

This intensity decreases as we move away from the center.

|-
|| Click on '''Width of slit '''and enter 3000 nm. 
|| In the green panel, click on the '''Width of slit '''text-box and enter 3000 nm.

|-
|| Cursor on the screen.

Point to bright and dark fringes.
|| Observe that a number of alternate dark and bright fringes are formed

|-
|| Click on the '''Maxima''' drop down.

Cursor on the 0 degrees in the drop down.

Point to the relative intensity.
|| Now click on the '''Maxima''' drop down.

Observe that the central maxima is at 0 degrees.

It shows '''Relative intensity''' as 1. This is the maximum intensity.

|-
|| Select K=1 from the '''Maxima''' drop down.
|| From the '''Maxima''' drop down select k=1.

|-
|| Point to '''Relative intensity''' value.
|| Here the''' Relative intensity''' decreases from 1 to 0.0472. 

|-
|| Click on '''Maxima''' drop down.

Select K=2.
|| Again click on '''Maxima''' drop down and select k=2.

|-
|| Point to '''Relative intensity''' value.
|| The '''Relative intensity '''decreases to 0.0165.

|-
|| Click on '''Minima''' drop down and select K=2.
|| Know Click on the''' Minima''' drop down and select k<nowiki>=2.</nowiki>

|-
|| Point to '''Relative intensity''' value.
|| The value of '''Relative intensity''' is shown as 0.

|-
|| Click on '''Minima '''drop down and select K<nowiki>=4</nowiki>
|| Click on '''Minima '''drop down and select k=4.

|-
|| Point to '''Relative intensity''' value.
|| Note that for every dark fringe the value of relative intensity will remain zero.

|-
|| 
|| Here I have made the table to show the relative intensity for maxima and minima.

|-
|| '''Slide Number 8 '''

'''Tabular Column'''

Table is given at the end.
|| Observe the relative intensity for maxima.


The Relative intensity decreases as we move away from central region. 

For the each minima, we have seen that the value remains zero for the relative '''intensity'''.

|-
|| Drag the slider of '''Wavelength''' to its lowest.

Cursor on the voilet light.
|| Drag the '''Wavelength slider '''to its highest value that is to 780 nm.

This is the region of red light.

|-
|| Click on the '''Maxima''' drop down.

Move the cursor through the drop down.
|| Next click on '''Maxima '''drop down.

Here we see four bright fringes.

|-
|| Drag the slider of '''Wavelength''' to its highest.

Cursor on the red light.
|| Next drag the slider of '''Wavelength''' to its lowest value that is to 380 nm.

This is the region of violet light.

|-
|| Click on the '''Maxima''' drop down.

Move the cursor through the drop down.
|| Now click on the '''Maxima''' drop down.

Here we can see eight positions for bright fringes.

|-
|| Cursor on the interface.
|| This happens because violet light refracts more than red light.

Hence we see more number of bright fringes for violet light.

|-
|| Drag the '''Wavelength''' slider to 520 nm.
|| Drag the '''Wavelength''' slider to 520 nm.

|-
|| Click on '''Maxima''' drop down.
|| Click on '''Maxima''' drop down and select first bright fringe.

|-
|| Point to the angle next to k=1.
|| Here the first bright fringe is formed at an angle of 14.4 degrees.

|-
|| Drag '''Wavelength''' slider to 720 nm.
|| Again drag the slider of '''Wavelength''' to 720 nm

|-
|| Click on the '''Maxima '''drop down.

Select k=1.
|| Click on the '''Maxima '''drop down and select K=1.

|-
|| Point to the angle next to k=1.
|| Here the first bright fringe is formed at an angle of 20.1 degrees.

Hence we conclude that if we increase the wavelength, angle also increases.

|-
|| Scroll down the screen.

|| Scroll down the screen.

This is shown in the formula.

|-
|| Cursor on the formula.

Point to the formula and also both angle and wavelength.
|| Here, the angle is directly proportional to the wavelength.

|-
|| '''Slide Number 9'''

'''Assignment'''

Change the wavelength to 380 nm and width of slit to 5000 nm.

Use the table as shown earlier in this tutorial for your referernce.

Tabulate the total number of maxima and minima.
|| As an assignment,

Change the wavelength to 380 nm and width of slit to 5000 nm.


Use the table as shown earlier in this tutorial for your referernce.


Tabulate the total number of maxima and minima.

|-
|| '''Slide Number 10'''

'''Assignment'''

For each maxima tabulate the value of relative intensity from the App.

Explain the diffraction pattern 
|| For each maxima tabulate the value of relative intensity from the App.

Explain the diffraction pattern

|-
|| '''Slide Number 11'''

'''Assignment'''

'''Diffrentiate between interference and diffraction patterns.'''
|| Differentiate between interference and diffraction patterns.

|-
|| 
|| Let us summarize.
|-
|| '''Slide Number 12'''

'''Summary'''
|| In this tutorial we have,
* Verified the relation between wavelength and relative intensity.
* Found the relation between slit width, maxima and minima.
* Calculated the angle for the given maxima.
* Interpreted diffraction intensity profile.
* Verified the relation between wavelength and angle.

|-
|| '''Slide Number 13'''

'''Acknowledgement'''

These Apps are created by Walter-fendt and his team.
|| These Apps are created by Walter-fendt and his team.

|-
|| '''Slide Number 14'''

'''About Spoken Tutorial project.'''
|| The video at the following link summarizes the Spoken Tutorial project.

Please download and watch it.

|-
|| '''Slide Number 15'''

'''Spoken Tutorial workshops.'''
|| The&nbsp;'''Spoken Tutorial Project&nbsp;'''team,

conducts workshops and gives certificates.

For more details, please write to us.

|-
|| '''Slide Number 16'''

'''Forum for specific questions'''
|| Please post your timed queries in this forum.

|-
|| '''Slide Number 17'''

'''Acknowledgement'''
|| Spoken Tutorial Project is funded by MHRD, Government of India.

|-
|| 
|| This is Himanshi Karwanje from IIT-Bombay. 

Thank you for joining.
|-
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