Apps-On-Physics/C3/Magnetism-and-Electromagnetism/English-timed

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Time Narration
00:01 Welcome to the Spoken Tutorial on Magnetism and Electromagnetism.
00;07 At the end of this tutorial you will be able to,
00:11 Draw magnetic field lines for a bar magnet.
00:15 Verify right hand thumb rule.
00:18 Verify Fleming's left hand and right hand rules.
00:23 Simulate the working of a generator.
00:26 Here I am using,

Ubuntu Linux OS version 16.04

00:32 Firefox web browser version 62.0.3
00:38 To follow this tutorial, learner should be familiar with Apps on Physics.
00:43 For the pre-requisites tutorials please visit this site.

https://spoken-tutorial.org/

00:49 In this tutorial we will use, Magnetic Field of a Bar Magnet
00:56 Magnetic Field of a Straight Current-Carrying Wire
01:00 Lorentz Force and Generator Apps.
01:04 I have already downloaded Apps on Physics to my Downloads folder.
01:09 Right click on magneticfieldbar_en.htm file.
01:15 Select Open With Firefox web Browser option.
01:19 Magnetic field bar App opens.
01:22 The App opens showing a magnet and a magnetic needle.
01:28 On the green panel there are two buttons.

Clear field lines and Turn magnet.

01:35 Poles of a bar magnet and compass needle are represented by the following colors.
01:41 Red for north pole and green for south pole.
01:46 Click on Turn magnet button.
01:49 Observe that both bar magnet and magnetic needle change their direction.
01:55 Let us draw the magnetic field lines.

Place the cursor on the magnetic needle.

02:02 Click on the magnetic needle and move the needle up and down to draw the magnetic lines.
02:09 Continue to draw the lines as shown here.
02:13 Click on the Clear field lines button.
02:17 Click on Turn magnet button.
02:20 Again draw the magnetic lines around the magnet.
02:25 When we turn the magnet, the lines of force change the direction.
02:30 The direction of magnetic field outside the bar magnet is from north to south.

It is shown by the arrows.

02:39 Magnetic field is strongest inside the bar magnet.
02:44 Outside the bar magnet it is strongest near the poles.
02:49 What is the direction of magnetic field inside the bar magnet?
02:55 Next we will move on to Magnetic Field Line in a Current Carrying Wire App.
03:00 Right click on magneticfieldwire_en.htm file.
03:06 Select Open with Firefox Web browser option.
03:10 The App opens showing magnetic field lines around a current carrying wire.
03:16 On the right side of the screen we have a Reverse current button.
03:22 The red arrow indicates the direction of the current.

Note that the direction of current is opposite to that of electrons.

03:33 The signs at the end of the wire symbolizes the terminals of the connected battery.
03:40 The concentric circles are the magnetic field around the current carrying wire.
03:46 Let us find the direction of magnetic field using right hand thumb rule.
03:53 Observe the picture and put your right hand as follows.
03:58 Put your right hand thumb in the direction of the current.
04:03 Now curl your fingers inside.
04:07 Fingers gives you the direction of magnetic field.
04:12 As an assignment,

Reverse the current flow and determine the magnetic field.

04:19 Let us move on to the next App, Lorentz Force.
04:24 Follow the same steps as we used for previous App to open htm file.
04:31 Interface shows a horseshoe magnet through which a conducting wire is passed.
04:37 The blue arrows shows the direction of the magnetic field.
04:42 On the green panel we have the following buttons.

On/Off , Reverse current and Turn magnet.

04:51 When the circuit is open, the wire is shown in black colour.
04:56 Click on the On/Off button to complete the circuit.
05:01 Notice that the wire is in conduction mode.
05:06 This is indicated by the red coloured wire.
05:10 At the bottom, there are three check-boxes.

These are Current direction, Magnetic field and Lorentz force.

05:20 The black arrow pointing towards right is the Lorentz force.
05:26 Lorentz force is always perpendicular to the magnetic field.
05:31 To change the direction of magnetic field, click on the Turn magnet button.
05:38 Let us verify the direction of Lorentz force using Fleming’s left-hand rule.
05:45 Press F5 key on the keyboard to restart the App.
05:50 First uncheck the Lorentz force check-box.
05:54 Click on On/Off button.
05:57 Now keep your fingers of the left hand as suggested here.
06:03 Index finger pointing in the direction of magnetic field. Middle finger pointing in the direction of current.
06:13 Thumb shows the direction of Lorentz force.
06:17 Here the direction of Force is towards the right-side.

This is Fleming’s left-hand rule.

06:25 Let us verify our answer by checking the Lorentz force check-box.
06:31 Observe that the direction is same as shown in the App.
06:36 As an assignment

Reverse the current flow.

06:40 Determine the direction of lorentz force using Fleming’s left hand rule.
06:47 Now let us open the Generator App.
06:51 I will open the App as before.
06:55 The App shows a generator.
06:58 An electrical generator converts mechanical energy into electrical energy.
07:05 The App opens showing a horseshoe magnet.
07:09 A rectangular current carrying coil is inserted between the poles of the magnet.
07:15 On the green panel, we can change the rotations per minute using the slider.
07:22 By default the rectangular coil rotates 6 rotations per minute.
07:28 We can change the rotation of the coil to a maximum of 12 rotations per minute.
07:35 Increase the rotation to 12 rotations per minute.
07:40 In the graph we can see two complete cycles in one minute.
07:46 Here the frequency of the maximum output voltage is doubled.
07:52 The rectangular coil is connected to the voltage source through the slip rings.
07:58 Observe that the rectangular coil is rotating about an axis.

This coil is perpendicular to the magnetic field.

08:09 Here rotation of the rectangular coil is a source of mechanical energy.
08:16 Due to the rotation of the coil, current is induced into the wire.
08:22 The red arrow represents the direction of the induced current.
08:27 In the green panel we can choose an AC generator or DC generator.
08:34 By default Without commutator an AC generator is selected.
08:40 Select With commutator radio button.
08:44 Commutator is a device for reversing the direction of flow of current.
08:50 This device ensures that the current flows only in direct current mode.
08:57 Hence With Commutator means, the generator is a DC generator.
09:03 On the top of the circuit, voltage v/s time graph is plotted.
09:09 This is the graph of a DC generator.
09:13 In the graph, moving blue point indicates the change in voltage.
09:19 Change direction button changes the direction of the rectangular coil.
09:25 Click on the Change direction button.
09:28 Observe the change in the direction of rectangular coil.

Also notice the change in the graph.

09:37 Press F5 key on the keyboard to restart the App.
09:42 We can find the direction of induced current using Fleming’s right-hand rule.
09:49 This rule is same as Fleming’s left-hand rule.
09:53 Click on the Pause button.
09:56 Now arrange fingers of your right hand as shown in the figure.
10:01 We can determine the direction of magnetic field using Fleming's right hand rule.
10:07 There are three check-boxes at the bottom of the green panel.
10:12 Direction of movement, Magnetic field and Induced current.
10:18 Uncheck the Magnetic field check-box.

Notice that the magnetic field lines disappear.

10:27 In the similar way we can uncheck the remaining check-boxes if not required.
10:33 Press F5 key on the keyboard to restart the App.
10:38 AC generator is an alternating current generator.
10:43 So, here the graph shows positive as well as negative voltages.
10:49 As an assignment,

Change the rotations per minute to 0, 3.0, 6.0 and 9.0

10:57 Note the changes in the movement of the coil and graph.

Explain the reason for the changes.

11:06 Let us summarise
11:08 Using these Apps we have,

Drawn magnetic field lines of a bar magnet.

11:15 Verified right hand thumb rule.
11:18 Verified Fleming's left hand and right hand rules.
11:23 Simulated the working of a generator.
11:28 These Apps were created by Walter Fendt and his team.
11:33 The video at the following link summarises the Spoken Tutorial project.

Please download and watch it.

11:41 The Spoken Tutorial Projectteam, conducts workshops and gives certificates.

For more details, please write to us.

11:51 Please post your timed queries in this forum.
11:55 The Spoken Tutorial Project is funded by MHRD, Government of India.
12:01 This is Himanshi Karwanje from IIT-Bombay.

Thank you for joining.

Contributors and Content Editors

PoojaMoolya