PhET/C3/Photoelectric-Effect/English-timed
From Script | Spoken-Tutorial
| 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. |
