View source for PhET-Simulations-for-Chemistry/C3/Photoelectric-Effect/English-timed

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||'''Time'''
|'''Narration'''

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|| 00:01
|| Welcome to this tutorial on '''Photoelectric Effect''', '''PhET simulation'''.

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|| 00:07
|| In this tutorial, we will learn- how to use interactive '''PhET simulation''', '''Photoelectric Effect'''.

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|| 00:15
|| To follow this tutorial, learners should be familiar with topics in high-school science.

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|| 00:22
|| Here I am using- 

'''Ubuntu Linux OS''' version 14.04,

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|| 00:28
||'''Java''' version 1.7.0,

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|| 00:32
||'''Firefox Web Browser''' version 53.02.2.

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|| 00:38
|| Using this '''simulation''', students will be able to- 
1. Study Photoelectric Effect.

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|| 00:44
||2. Determine '''Threshold frequency'''.

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|| 00:47
||3. Find '''Stopping potential''' and '''Work function'''.

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|| 00:51
||4. Study the factors affecting current and energy of electrons.

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|| 00:56
|| When light of a particular frequency strikes a metal surface, electrons are ejected.

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|| 01:04
||Ejected electrons are counted by a detector that measures their kinetic energy.

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|| 01:11
|| Use the given '''link''' to download the '''simulation'''.

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|| 01:15
|| I have already downloaded the '''Photoelectric Effect''' simulation to my '''Downloads''' folder.

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|| 01:22
|| Open the '''terminal'''.

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|| 01:24
||At the prompt, type: '''cd Downloads''' and press '''Enter'''.

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|| 01:29
||Then type: '''java space hyphen jar space photoelectric_en.jar''' and press '''Enter'''.

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|| 01:40
||'''Photoelectric Effect''' simulation opens.

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|| 01:44
|| Do not close the terminal, it will '''kill''' the process.

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|| 01:49
|| Click '''Cancel''' to continue.

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|| 01:52
|| This is the '''interface''' of '''Photoelectric Effect''' simulation.

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|| 01:57
|| This '''screen''' has a menu bar with menu items- '''File''', '''Options''' and '''Help'''.

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|| 02:05
|| '''Options''' menu has two options, '''Show photons''' and '''Control photon number instead of intensity'''.

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|| 02:14
|| Screen has a lamp to shine light on the metal surface.

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|| 02:19
|| We can change '''Intensity''' and wavelength by dragging the respective '''slider'''s.

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|| 02:26
|| We can also input '''Intensity''' and wavelength values in their respective boxes. 

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|| 02:33
|| '''Photoelectric''' effect is carried out inside a vacuum chamber.

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|| 02:38
|| A vacuum chamber consists of a metal surface and a detector to measure kinetic energy of electrons.

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|| 02:48
|| A battery and a current indicator are connected in the circuit.

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|| 02:53
|| Battery is provided with a Voltage slider.

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|| 02:58
|| A '''Play/Pause''' and '''Step''' buttons are at the bottom of the '''screen'''.

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|| 03:04
|| On the right side of the screen, we can see a '''Target''' drop down box to choose metals.

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|| 03:11
|| By default, '''Sodium''' is selected as '''Target''' metal. 

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|| 03:16
|| For accuracy in results, let's move the '''Intensity''' slider to '''50%'''. 

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|| 03:23
|| In '''Options''' menu, click on '''Show photons''' option.

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|| 03:28
|| Observe that light is shined in the form of photons.

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|| 03:34
|| Un-check '''Show photons''' option.

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|| 03:36
|| By default, the wavelength slider is at '''400 nano-meter'''. 

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|| 03:42
|| Electrons are ejected as soon as light falls on Sodium metal surface.

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|| 03:48
|| There is no time lag between incident radiation and electrons emission. 

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|| 03:54
|| These electrons flow towards a detector.

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|| 03:58
|| For '''0 V''' (zero voltage), value of current is shown as '''0.071'''.

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|| 04:05
|| Under '''Graphs''', we have the following check boxes -

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|| 04:09
|| '''Current Vs battery voltage''',

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|| 04:12
|| '''Current Vs light intensity''',

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|| 04:15
|| '''Electron energy Vs light frequency'''.

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|| 04:19
|| Click on '''Current vs battery voltage''' check box. 

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|| 04:23
|| We see a graph of '''current vs battery voltage'''. 

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|| 04:29
|| Notice a red dot on the graph.

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|| 04:32
|| Drag the voltage slider slowly from 0 to 6.00 volts. 

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|| 04:38
|| Notice that current remains constant as we increase the voltage.

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|| 04:44
|| This is indicated by the red line.

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|| 04:48
|| As we increase the voltage, speed of photoelectrons increases.

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|| 04:53
|| Let us see how intensity of light affects the current.

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|| 04:58
|| Click on '''Current vs light intensity''' check box.

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|| 05:03
|| Drag the '''Intensity''' slider upto 90%.

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|| 05:08
|| Notice that '''current''' increases linearly with the increase in '''intensity'''.

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|| 05:14
|| This is indicated by the green line.

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|| 05:18
|| Increase in intensity of light increases the magnitude of photoelectric current.

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|| 05:24
|| Now Current value is shown as 0.127.

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|| 05:30
|| Drag the '''Intensity''' slider back to 50%.

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|| 05:35
|| Now, click on '''Electron energy Vs light Frequency''' graph check box.

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|| 05:42
|| Drag the wavelength slider towards '''UV''' region.

Observe the graphs.

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|| 05:49
|| Notice that energy increases linearly with the increase in Frequency.

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|| 05:55
|| This is indicated by the blue line.

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|| 05:59
|| Observe the change in current.

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|| 06:02
|| Increase in frequency, increases the energy of photoelectrons.

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|| 06:08
|| As frequency increases, energy transfer from photons to electrons increases.

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|| 06:15
|| This results in increase in the kinetic energy of ejected electrons.

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|| 06:21
|| Now click on a '''Camera''' icon.

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|| 06:24
|| A snapshot window opens.

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|| 06:27
|| It gives information about '''Graphs''' and '''Experimental Parameters'''.

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|| 06:33
|| Using this snapshot, we can compare graphs with different settings.

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|| 06:39
|| Close the snapshot window.

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|| 06:42
|| Now we will discuss how to calculate the '''Threshold Frequency'''.

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|| 06:48
|| Each metal has a characteristic minimum frequency to cause photoelectric emission.

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|| 06:55
|| This frequency is, '''Threshold Frequency''', denoted by '''ʋ<sub>0'''.</sub>

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|| 07:01
|| Below the '''Threshold Frequency''', Photoelectric Effect is not observed.

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|| 07:07
|| Drag the wavelength slider towards visible region.

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|| 07:12
|| Observe the wavelength at which electron ejection stops.

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|| 07:18
|| Notice that at '''540 nm''' no more electrons are ejected from '''Sodium'''. 

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|| 07:25
|| Let's type '''539 nm''' in the wavelength text box and observe.

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|| 07:32
|| At '''539 nm''' electrons start ejecting from sodium metal surface.

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|| 07:39
|| It means that, '''539 nm''' is threshold wavelength for '''Sodium'''.

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|| 07:45
|| Here, value of current is 0.00.

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|| 07:49
|| Now let us calculate the '''threshold frequency''' value.

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|| 07:54
|| Here wavelength is shown in '''nano metres(nm)'''.

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|| 07:58
|| I will convert it to metres by multiplying with 10 to the power of -9

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|| 08:05
|| '''Threshold frequency''' can be calculated using following formula.

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|| 08:10
|| '''Threshold frequency''' of '''sodium''' is '''0.56 x 10 to the power of 15 </sup>Hz'''. 

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|| 08:18
|| Now let us select '''Platinum''' as '''Target'''.

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|| 08:22
|| Click on drop down arrow and select '''Platinum'''.

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|| 08:26
|| At this wavelength we do not see ejection of photoelectrons.

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|| 08:31
|| Drag the slider to '''UV''' region untill electron ejection starts.

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|| 08:39
|| Drag the wavelength slider to lower wavelength region.

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|| 08:45
|| Notice that a large number of electrons with different energies are ejected.

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|| 08:52
|| To view electrons with highest energy, click on '''Show only highest energy electrons''' check box.

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|| 09:00
|| Uncheck the box to show electrons with different energies.

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|| 09:05
|| As an assignment, calculate the '''Threshold Frequency''' of '''Platinum'''.

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|| 09:11
|| We will move on to the calculation of '''work function''' and '''stopping voltage'''.

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|| 09:17
|| '''Work function''' is minimum amount of energy necessary to start photoelectric emission. 

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|| 09:24
|| Different metals have different values of work function.

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|| 09:29
|| It is denoted by '''ϕ<sub>0'''</sub>. 

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||09:32
|| Work function is given by '''ϕ<sub>0</sub><nowiki>= hʋ</nowiki><sub>0'''</sub>.

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|| 09:38
|| Elements with low ionization enthalpy values have low work function.

Example: Lithium, Sodium, Potassium, Rubidium, and Caesium.

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||09:51
|| Let us calculate the work function for Sodium.

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|| 09:55
|| Work function is calculated by using following formula.

'''w<sub>0 =</sub> hʋ<sub>0 '''</sub>

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|| 10:04
|| Work function for Sodium is 2.31 eV.(electron volts) 

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|| 10:10
|| Similarly work function for Calcium is 2.9 eV (electron volts)

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|| 10:17
|| '''Stopping Potential'''- It is a negative voltage required to stop electrons from reaching the other side.

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|| 10:26
|| At Stopping Potential, photoelectric current becomes zero.

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|| 10:31
|| Let's see how to determine the stopping potential for '''Sodium'''.

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|| 10:37
|| Change '''Sodium''' as target metal.

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|| 10:41
|| Drag the wavelength slider to threshold wavelength of sodium.
That is '''539 nano-meter'''.

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|| 10:51
|| Drag the voltage slider to negative voltage.

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|| 10:56
|| At which voltage, electrons will bounce off from detector?

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|| 11:01
|| At '''-0.01 V'''(volts), electrons start to bounce off from detector.

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|| 11:08
|| Observe, at '''-0.04 Volts''', no electrons are ejected from sodium. 

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|| 11:16
|| As an assignment, calculate the work function for Zinc, Copper and Calcium.

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|| 11:22
|| Determine the stopping potential for the same metals.

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|| 11:27
|| Let us summarize. In this tutorial we have learnt about,

'''Photoelectric Effect''', PhET simulation.

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||11:36
|| Using this simulation, we have learnt  about: Photoelectric Effect,

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|| 11:41
||  to determine '''Threshold Frequency''',

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|| 11:44
||  to find '''Stopping Potential''' and '''Work Function''' and

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|| 11:48
||  study the factors affecting current and energy of electrons.

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|| 11:54
|| The video at the following link summarizes the '''Spoken Tutorial''' project.

Please download and watch it.

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|| 12:03
|| The Spoken Tutorial Project team conducts workshops using spoken tutorials and
gives certificates on passing online tests.

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|| 12:13
|| For more details, please write to us.

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|| 12:17
|| Please post your timed queries on this forum.

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|| 12:22
|| This project is partially funded by Pandit Madan Mohan Malaviya National Mission on Teachers and Teaching.

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|| 12:31
|| Spoken Tutorial Project is funded by '''NMEICT, MHRD,''' Government of India.

More information on this mission is available at this link.

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|| 12:43
|| This is Meenal Ghoderao from IIT Bombay.

Thank you for joining.
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