PhET/C3/Photoelectric-Effect/English-timed

Time	Narration
00:01	Welcome to this tutorial on Photoelectric Effect, PhET simulation.
00:07	In this tutorial, we will learn- how to use interactive PhET simulation, Photoelectric Effect.
00:15	To follow this tutorial, learners should be familiar with topics in high-school science.
00:22	Here I am using- Ubuntu Linux OS version 14.04,
00:28	Java version 1.7.0,
00:32	Firefox Web Browser version 53.02.2.
00:38	Using this simulation, students will be able to- 1. Study Photoelectric Effect.
00:44	2. Determine Threshold frequency.
00:47	3. Find Stopping potential and Work function.
00:51	4. Study the factors affecting current and energy of electrons.
00:56	When light of a particular frequency strikes a metal surface, electrons are ejected.
01:04	Ejected electrons are counted by a detector that measures their kinetic energy.
01:11	Use the given link to download the simulation.
01:15	I have already downloaded the Photoelectric Effect simulation to my Downloads folder.
01:22	Open the terminal.
01:24	At the prompt, type: cd Downloads and press Enter.
01:29	Then type: java space hyphen jar space photoelectric_en.jar and press Enter.
01:40	Photoelectric Effect simulation opens.
01:44	Do not close the terminal, it will kill the process.
01:49	Click Cancel to continue.
01:52	This is the interface of Photoelectric Effect simulation.
01:57	This screen has a menu bar with menu items- File, Options and Help.
02:05	Options menu has two options, Show photons and Control photon number instead of intensity.
02:14	Screen has a lamp to shine light on the metal surface.
02:19	We can change Intensity and wavelength by dragging the respective sliders.
02:26	We can also input Intensity and wavelength values in their respective boxes.
02:33	Photoelectric effect is carried out inside a vacuum chamber.
02:38	A vacuum chamber consists of a metal surface and a detector to measure kinetic energy of electrons.
02:48	A battery and a current indicator are connected in the circuit.
02:53	Battery is provided with a Voltage slider.
02:58	A Play/Pause and Step buttons are at the bottom of the screen.
03:04	On the right side of the screen, we can see a Target drop down box to choose metals.
03:11	By default, Sodium is selected as Target metal.
03:16	For accuracy in results, let's move the Intensity slider to 50%.
03:23	In Options menu, click on Show photons option.
03:28	Observe that light is shined in the form of photons.
03:34	Un-check Show photons option.
03:36	By default, the wavelength slider is at 400 nano-meter.
03:42	Electrons are ejected as soon as light falls on Sodium metal surface.
03:48	There is no time lag between incident radiation and electrons emission.
03:54	These electrons flow towards a detector.
03:58	For 0 V (zero voltage), value of current is shown as 0.071.
04:05	Under Graphs, we have the following check boxes -
04:09	Current Vs battery voltage,
04:12	Current Vs light intensity,
04:15	Electron energy Vs light frequency.
04:19	Click on Current vs battery voltage check box.
04:23	We see a graph of current vs battery voltage.
04:29	Notice a red dot on the graph.
04:32	Drag the voltage slider slowly from 0 to 6.00 volts.
04:38	Notice that current remains constant as we increase the voltage.
04:44	This is indicated by the red line.
04:48	As we increase the voltage, speed of photoelectrons increases.
04:53	Let us see how intensity of light affects the current.
04:58	Click on Current vs light intensity check box.
05:03	Drag the Intensity slider upto 90%.
05:08	Notice that current increases linearly with the increase in intensity.
05:14	This is indicated by the green line.
05:18	Increase in intensity of light increases the magnitude of photoelectric current.
05:24	Now Current value is shown as 0.127.
05:30	Drag the Intensity slider back to 50%.
05:35	Now, click on Electron energy Vs light Frequency graph check box.
05:42	Drag the wavelength slider towards UV region. Observe the graphs.
05:49	Notice that energy increases linearly with the increase in Frequency.
05:55	This is indicated by the blue line.
05:59	Observe the change in current.
06:02	Increase in frequency, increases the energy of photoelectrons.
06:08	As frequency increases, energy transfer from photons to electrons increases.
06:15	This results in increase in the kinetic energy of ejected electrons.
06:21	Now click on a Camera icon.
06:24	A snapshot window opens.
06:27	It gives information about Graphs and Experimental Parameters.
06:33	Using this snapshot, we can compare graphs with different settings.
06:39	Close the snapshot window.
06:42	Now we will discuss how to calculate the Threshold Frequency.
06:48	Each metal has a characteristic minimum frequency to cause photoelectric emission.
06:55	This frequency is, Threshold Frequency, denoted by ʋ0.
07:01	Below the Threshold Frequency, Photoelectric Effect is not observed.
07:07	Drag the wavelength slider towards visible region.
07:12	Observe the wavelength at which electron ejection stops.
07:18	Notice that at 540 nm no more electrons are ejected from Sodium.
07:25	Let's type 539 nm in the wavelength text box and observe.
07:32	At 539 nm electrons start ejecting from sodium metal surface.
07:39	It means that, 539 nm is threshold wavelength for Sodium.
07:45	Here, value of current is 0.00.
07:49	Now let us calculate the threshold frequency value.
07:54	Here wavelength is shown in nano metres(nm).
07:58	I will convert it to metres by multiplying with 10 to the power of -9
08:05	Threshold frequency can be calculated using following formula.
08:10	Threshold frequency of sodium is 0.56 x 10 to the power of 15 </sup>Hz.
08:18	Now let us select Platinum as Target.
08:22	Click on drop down arrow and select Platinum.
08:26	At this wavelength we do not see ejection of photoelectrons.
08:31	Drag the slider to UV region untill electron ejection starts.
08:39	Drag the wavelength slider to lower wavelength region.
08:45	Notice that a large number of electrons with different energies are ejected.
08:52	To view electrons with highest energy, click on Show only highest energy electrons check box.
09:00	Uncheck the box to show electrons with different energies.
09:05	As an assignment, calculate the Threshold Frequency of Platinum.
09:11	We will move on to the calculation of work function and stopping voltage.
09:17	Work function is minimum amount of energy necessary to start photoelectric emission.
09:24	Different metals have different values of work function.
09:29	It is denoted by ϕ0.
09:32	Work function is given by ϕ0= hʋ0.
09:38	Elements with low ionization enthalpy values have low work function. Example: Lithium, Sodium, Potassium, Rubidium, and Caesium.
09:51	Let us calculate the work function for Sodium.
09:55	Work function is calculated by using following formula. w0 = hʋ0
10:04	Work function for Sodium is 2.31 eV.(electron volts)
10:10	Similarly work function for Calcium is 2.9 eV (electron volts)
10:17	Stopping Potential- It is a negative voltage required to stop electrons from reaching the other side.
10:26	At Stopping Potential, photoelectric current becomes zero.
10:31	Let's see how to determine the stopping potential for Sodium.
10:37	Change Sodium as target metal.
10:41	Drag the wavelength slider to threshold wavelength of sodium. That is 539 nano-meter.
10:51	Drag the voltage slider to negative voltage.
10:56	At which voltage, electrons will bounce off from detector?
11:01	At -0.01 V(volts), electrons start to bounce off from detector.
11:08	Observe, at -0.04 Volts, no electrons are ejected from sodium.
11:16	As an assignment, calculate the work function for Zinc, Copper and Calcium.
11:22	Determine the stopping potential for the same metals.
11:27	Let us summarize. In this tutorial we have learnt about, Photoelectric Effect, PhET simulation.
11:36	Using this simulation, we have learnt about: Photoelectric Effect,
11:41	to determine Threshold Frequency,
11:44	to find Stopping Potential and Work Function and
11:48	study the factors affecting current and energy of electrons.
11:54	The video at the following link summarizes the Spoken Tutorial project. Please download and watch it.
12:03	The Spoken Tutorial Project team conducts workshops using spoken tutorials and gives certificates on passing online tests.
12:13	For more details, please write to us.
12:17	Please post your timed queries on this forum.
12:22	This project is partially funded by Pandit Madan Mohan Malaviya National Mission on Teachers and Teaching.
12:31	Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India. More information on this mission is available at this link.
12:43	This is Meenal Ghoderao from IIT Bombay. Thank you for joining.

Contributors and Content Editors

Madhurig, PoojaMoolya, Sandhya.np14