View source for PhET/C2/Photoelectric-Effect/English

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

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

'''Title slide'''
|| Welcome to this tutorial on '''Photoelectric Effect''', '''PhET simulation'''.
|-
|| '''Slide Number 2'''

'''Learning objectives'''
|| In this tutorial we will learn-

How to use Interactive '''PhET simulation''', '''Photoelectric Effect'''.
|-
|| '''Slide Number 3'''

'''Pre-requisites'''
|| To follow this tutorial,

Learners should be familiar with topics in high school science.
|-
|| '''Slide Number 4'''

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

Ubuntu Linux OS version 14.04

Java version 1.7.0

Firefox Web Browser version 53.02.2.
|-
|| '''Slide Number 5'''

'''Learning Goals'''
|| Using this simulation, students will be able to-

Study '''Photoelectric Effect'''.

Determine '''Threshold frequency'''.

Find '''Stopping potential''' and '''Work function'''.

Study the factors affecting current and energy of electrons.
|-
|| '''Slide Number 6'''

'''Photoelectric Effect'''
|| When light of a particular frequency strikes a metal surface, electrons are ejected.

Ejected electrons are counted by a detector that measures their kinetic energy.
|-
|| '''Slide Number 7'''

'''Link for PhET simulation'''

[http://phet.colorado.edu/ http://phet.colorado.edu]
|| Use the given link to download the simulation.

[http://phet.colorado.edu/ http://phet.colorado.edu]
|-
|| Point to '''Photoelectric Effect''' phet.
|| I have already downloaded the '''Photoelectric Effect''' simulation to my '''Downloads''' folder.
|-
|| To open java file,

Press '''Ctrl+Alt+T''' keys.

Type '''cd Downloads''' and press enter.

Type '''java space hyphen jar photoelectric_en.jar''' and press enter.

Point to interface.
|| Open the terminal.

At the prompt type '''cd Downloads''' and press enter.

Then type, '''java space hyphen jar space photoelectric_en.jar''' and press enter.

'''Photoelectric Effect''' simulation opens.
|-
|| Note.

Point to the terminal.

Click '''Cancel'''.
|| Do not close the terminal, it will kill the process.

Click '''Cancel''' to continue.
|-
|| Point to the interface.
|| This is the interface of '''Photoelectric Effect''' simulation.
|-
|| Point to '''File''', '''Options''' and '''Help'''.

Click on '''Options''' menu.

Point to '''Show photons''' and

'''Control photon number instead of intensity'''.
|| This screen has a menu bar, with menu items,

'''File''', '''Options''' and '''Help'''.

'''Options''' menu has two options,

'''Show photons''' and

'''Control photon number instead of intensity'''.
|-
|| Point to lamp.
|| Screen has a lamp to shine light on the metal surface.
|-
|| Point to '''Intensity''' and wavelength sliders.

Point to '''Intensity''' and wavelength texboxes.
|| We can change '''Intensity''' and wavelength by dragging the respective sliders.

We can also input '''Intensity''' and wavelength values in their respective boxes. 
|-
|| Point to vacuum chamber.
|| '''Photoelectric Effect''' is carried out inside a vacuum chamber.
|-
|| Point to vacuum chamber.

point to metal surface.

point to Detector.
|| A vacuum chamber consists of -

A metal surface and a detector to measure kinetic energy of electrons.
|-
|| Point to battery and current indicator 

Point to voltage slider.
|| A battery and a current indicator are connected in the circuit.

Battery is provided with a Voltage slider.
|-
|| Point to '''Play/Pause''' and '''Step''' buttons.
|| A '''Play/Pause''' and '''Step''' buttons are at the bottom of the screen.
|-
|| Point to and scroll down '''Target''' drop down box.

Point to '''Sodium''' Target.
|| On the right-side of the screen, we can see, a '''Target''' drop down box to choose metals.

By default '''Sodium''' is selected as Target metal. 
|-
|| Drag the '''Intensity''' slider to '''50%'''.

Click on '''Show photons''' option.

Point to the photons.

Uncheck '''Show photons''' option.
|| For accuracy in results let's move the '''Intensity''' slider to '''50%'''. 

In '''Options''' menu click on '''Show photons''' option.

Observe that light is shined in the form of photons.

Uncheck '''Show photons''' option.
|-
|| Point to wavelength slider at '''400nm'''.

Point to electrons.

Point to detector.
|| By default the wavelength slider is at '''400nm'''. 

Electrons are ejected as soon as light falls on Sodium metal surface.

There is no time lag between incident radiation and electrons emission. 

These electrons flow towards a detector.
|-
|| Point to current.
|| For '''0 V''' (zero voltage) value of current is shown as '''0.071'''.
|-
|| Point to '''Graphs''' check boxes.
|| Under '''Graphs''' we have the following check boxes -

'''Current Vs battery voltage'''

'''Current Vs light intensity'''

'''Electron energy Vs light frequency'''.
|-
|| Click on '''Current vs battery voltage''' check box.

Point to graph.

Point to the red dot.
|| Click on '''Current vs battery voltage''' check box. 

We see a graph of '''current vs battery voltage'''. 

Notice a red dot on the graph.
|-
|| Drag the voltage slider from '''0''' to '''6.00''' volts. 

Point to Graph.

Point to red line.

Point to electrons.
|| Drag the voltage slider slowly from '''0''' to '''6.00''' volts. 

Notice that current remains constant as we increase the voltage.

This is indicated by the red line.

As we increase the voltage, speed of photoelectrons increases.
|-
|| Click on '''Current vs light intensity''' check box.

Drag the '''Intensity''' slider upto '''90%'''.
|| Let us see how intensity of light affects the current.

Click on '''Current vs light intensity''' check box.

Drag the '''Intensity''' slider upto '''90%'''.
|-
|| Point to graph.

Point to green line.
|| Notice that '''current''' increases linearly with the increase in '''intensity'''.

This is indicated by the green line.
|-
|| 
|| Increase in intensity of light increases the magnitude of photoelectric current.
|-
|| Point to current meter.
|| Now Current value is shown as '''0.127'''.
|-
|| Drag the '''Intensity''' slider to '''50%'''.
|| Drag the '''Intensity''' slider back to '''50%'''.
|-
|| Click on '''Electron energy VS light Frequency''' graph check box.
|| Now click on '''Electron energy Vs light Frequency''' graph check box.
|-
|| Drag the wavelength slider towards '''UV''' region.

Point to graphs.

Point to blue line

Point to current value.
|| Drag the wavelength slider towards '''UV''' region.

Observe the graphs.

Notice that energy increases linearly with the increase in Frequency'''.

This is indicated by the blue line.

Observe the change in current.

Increase in frequency, increases the energy of photoelectrons.
|-
|| Point to the graph.
|| As frequency increases, energy transfer from photons to electrons increases.

This results in increase in the kinetic energy of ejected electrons.
|-
|| Click on Camera icon.

Point to snapshot window.

Point to Graphs.

Click on close button.
|| Now click on a '''Camera''' icon.

A snapshot window opens.

It gives information about '''Graphs''' and '''Experimental Parameters'''.

Using this snapshot, we can compare graphs with different settings.

Close the snapshot window.
|-
|| 
|| Now we will discuss how to calculate the '''Threshold Frequency'''.
|-
|| '''Slide Number 8'''

'''Threshold frequency'''
|| Each metal has a characteristic minimum frequency to cause photoelectric emission.

This frequency is, '''Threshold Frequency''', denoted by '''ʋ<sub>0'''.</sub>

Below the '''Threshold Frequency''', '''Photoelectric Effect''' is not observed.
|-
|| Drag the wavelength slider towards visible region.
|| Drag the wavelength slider towards visible region.

Observe the wavelength at which electron ejection stops.
|-
|| Point to '''540 nm'''.
|| Notice that at '''540 nm''' no more electrons are ejected from '''Sodium'''. 

|-
|| Type '''539 nm''' in wavelength texbox.

point to Current meter.

point to electrons.

Point to '''539 nm'''.

Point to Current meter.
|| Let's type '''539 nm''' in the wavelength text box and observe.

At '''539 nm''' electrons start ejecting from sodium metal surface.

It means that, '''539 nm''' is threshold wavelength for '''Sodium'''.

Here, value of current is '''0.00'''.
|-
|| 
|| Now let us calculate the threshold frequency value.
|-
|| '''Slide Number 9'''

Threshold frequency calculation for sodium.

539 nm = 539 x 10<sup>-9 </sup>m.

Frequency can be calculated using following formula.

c= ʋλ, ʋ = c/λ

ʋ <nowiki>= (</nowiki>3 x 10<sup>8m/s</sup>)/ (539 x 10<sup>-9m</sup>)

ʋ<nowiki>= 0.56 x 10</nowiki><sup>15</sup>'''Hz'''.
|| Here wavelength is shown in '''nano metres(nm)'''.

I will convert it to metres by multiplying with 10<sup>-9.</sup>

'''Threshold frequency''' can be calculated using following formula.

'''Threshold frequency''' of '''sodium''' is '''0.56 x 10<sup>15 </sup>Hz'''. 
|-
|| Click on drop down arrow and select '''Platinum'''.
|| Now let us select '''Platinum''' as '''Target'''.

Click on drop down arrow and select '''Platinum'''.
|-
|| Point to the wavelength value.

Drag the slider to '''UV '''region.
|| At this wavelength we do not see ejection of photoelectrons.
Drag the slider to '''UV''' region untill electron ejection starts.
|-
|| Drag the wavelength slider to lower wavelength region.

Point to the ejected electrons.
|| Drag the wavelength slider to lower wavelength region.

Notice that a large number of electrons with different energies are ejected.
|-
|| Click on '''Show only highest energy electrons''' check box.

Uncheck the box.
|| To view electrons with highest energy, click on '''Show only highest energy electrons''' check box.

Uncheck the box to show electrons with different energies.
|-
|| '''Slide Number 10'''

'''Assignment'''
|| As an assignment, 

Calculate the Threshold Frequency of '''Platinum'''.
|-
|| 
|| we will move on to the calculation of '''work function''' and '''stopping voltage'''.
|-
|| '''Slide Number 11'''

'''Work Function'''
|| '''Work function''' is minimum amount of energy necessary to start photoelectric emission. 

Different metals have different values of work function.

It is denoted by '''ϕ<sub>0'''</sub>. 
|-
|| '''Slide Number 12'''

'''Work function'''
|| Work function is given by '''ϕ<sub>0</sub><nowiki>= hʋ</nowiki><sub>0'''</sub>.

Elements with low Ionization enthalpy values have low work function.

Example: Li, Na, K, Rb, and Cs.
|-
|| '''Slide Number 13'''

'''Work function for Sodium'''

For '''Sodium''', 

Ʋ<sub>0 = </sub>0.56 x 10<sup>15 </sup>hZ which we have calculated earlier.

'''w<sub>0 </sub><nowiki>= hʋ</nowiki><sub>0 '''</sub>

w<sub>0 </sub><nowiki>= 6.626 x 10</nowiki><sup>-34</sup>x0.56x10<sup>15</sup>

w<sub>0 </sub><nowiki>= 6.626 x 0.56 x 10</nowiki><sup>-19</sup>

w<sub>0 </sub><nowiki>= 3.711 x 10</nowiki><sup>-19 J</sup>

w<sub>0</sub> <nowiki>=3.711 x 10</nowiki><sup>-19 </sup>/ 1.60218<sup> </sup>x 10<sup>-19 </sup>

w<sub>0 <nowiki>=2.31 eV</nowiki></sub>
|| Let us calculate the work function for '''Sodium'''.

Work function is calculated by using following formula.

'''w<sub>0 =</sub> hʋ<sub>0 '''</sub>

Work function for '''Sodium''' is '''2.31eV'''.(electron volts) 
|-
|| '''Slide Number 14'''

'''Work function for Calcium'''

Formula for work function is '''w<sub>0 =</sub> hʋ<sub>0 '''</sub>

For '''Calcium''', 

Ʋ<sub>0 </sub><nowiki>=0.703 x 10</nowiki><sup>15 </sup>hZ 

w<sub>0 </sub><nowiki>= hʋ</nowiki><sub>0 </sub>

w<sub>0 </sub><nowiki>= 6.626 x 10</nowiki><sup>-34 </sup>x<sup> </sup>0.703 x 10<sup>15 </sup>

w<sub>0 </sub><nowiki>= 6.626 x </nowiki>0.703 x 10<sup>-19</sup>

w<sub>0 </sub><nowiki>= 4.66 x 10</nowiki><sup>-19</sup>/1.6021 X 10<sup>-19</sup>

wo=2.9 eV
|| Similarly work function for '''Calcium''' is '''2.9''' eV (electron volts)
|-
|| '''Slide Number 15'''

'''Stopping potential'''
|| '''Stopping Potential'''-

It is a negative voltage required to stop electrons from reaching the other side.

At Stopping Potential, photoelectric current becomes zero.
|-
|| Click on drop down arrow and select '''Sodium'''.

Drag wavelength slider to '''539 nm'''.
|| Let's see how to determine the stopping potential for '''Sodium'''.

Change '''Sodium''' as target metal.

Drag the wavelength slider to threshold wavelength of sodium.

That is '''539 nm'''.
|-
|| Drag the voltage slider to negative voltage.

Point to electrons.

Point to '''-0.04 V''' and electrons.
|| Drag the voltage slider to negative voltage.

At which voltage, electrons will bounce off from detector?

At '''-0.01 V'''(volts), electrons start to bounce off from detector.

Observe At '''-0.04 V''', no electrons are ejected from sodium. 
|-
|| '''Slide Number 16'''

'''Assignment'''
|| As an assignment,

Calculate the work function for '''Zinc''', '''Copper''' and '''Calcium'''.

Determine the stopping potential for the same metals.
|-
|| '''Slide Number 17'''

'''Summary'''
|| Let us summarize.

In this tutorial we have learnt about,

'''Photoelectric Effect''', PhET simulation.
|-
|| '''Slide number 18'''

'''Summary'''
|| Using this simulation, we have learnt,

# About '''Photoelectric Effect'''.
# To determine '''Threshold Frequency.'''
# To find '''Stopping Potential''' and '''Work Function''' and
# Study the factors affecting current and energy of electrons.
|-
|| '''Slide Number 19'''

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

Please download and watch it.
|-
|| '''Slide Number 20'''

'''Spoken Tutorial workshops'''
|| The '''Spoken Tutorial Project '''team:

conducts workshops using spoken tutorials and

gives certificates on passing online tests.

For more details, please write to us.
|-
|| '''Slide Number 21'''

'''Forum for specific questions:'''

Do you have questions in THIS '''Spoken Tutorial'''?

Please visit this site.

Choose the minute and second where you have the question.

Explain your question briefly.

Someone from our team will answer them.
|| Please post your timed queries on this forum.
|-
|| '''Slide Number 22'''

'''Acknowledgement'''
|| This project is partially funded by Pandit Madan Mohan Malaviya National Mission on Teachers and Teaching.
|-
|| '''Slide Number 23'''

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

More information on this mission is available at this link.
|-
|| 
|| This is Meenal Ghoderao from IIT Bombay.

Thank you for joining.
|-
|}