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Time Narration
00:01 Welcome to the spoken tutorial on Wheatstone Bridge and Potentiometer.
00:07 At the end of this tutorial you will be able to,

Simulate the working of wheatstone bridge.

Solve a numerical based on wheatstone bridge.

00:18 Simulate the working of potentiometer.

Solve a numerical based on potentiometer.

00:27 Here I am using,

Ubuntu Linux OS version 16.04

Firefox Web Browser version 62.0.3

00:40 To follow this tutorial, learner should be familiar with Apps on Physics.

For the Pre-requisites tutorials please visit this site.

00:51 In this tutorial we will use,

Wheatstone's Bridge and Potentiometer Apps.

00:59 To open the App, right-click on wheatstonebridge_en.htm file.

Select Open with Firefox Web Browser option.

01:12 The App opens in the browser.
01:15 Wheatstone’s bridge is a simple circuit for measuring the unknown resistance.
01:21 Meter bridge uses the same principle for practical purpose. First we will learn about the circuit connections.
01:31 The circuit shows a simple series-parallel arrangement of resistances.
01:37 The resistances are connected between the voltage supply and ground.
01:43 A galvanometer is connected between the two parallel branches of resistances.
01:49 Galvanometer is a device to detect small changes in current in the circuit.
01:56 The negative terminal of the galvanometer is connected to the wire of 1 cm.
02:03 The measurement of the wire is shown by the scale. We can drag the sliding contact along the wire.
02:11 In the green panel the Sliding resistor is that of the wire.
02:17 We can vary the Sliding resistor from 1 ohm to 1000 ohms.
02:23 In the green panel we can also edit the values of Comparable resistor . It is the standard resistance of the circuit.
02:33 Voltage of the power supply can take values from 1 to 10 Volts.
02:39 We can also change the Resistance of the meter.
02:43 Resistance of the meter depends on the comparable resistor.
02:48 At the bottom of control panel there are two check boxes.

Indicate voltage and Indicate amperage

02:56 Select both the check-boxes.
03:00 Observe that the values of voltage and current are shown in the circuit.
03:06 We can calculate the unknown resistance when the bridge is balanced.
03:12 Let us now see how to balance the bridge.
03:16 Press F5 key on the keyboard to restart the App.
03:20 Click on Indicate voltage and Indicate amperage check-boxes.
03:26 To balance the bridge, drag the sliding contact to get a zero amperage.
03:32 We can also drag the slider in the green panel to change the amperage.
03:38 Observe the value of voltage and current at each resistance.
03:44 The values are balanced in series-parallel arrangement of resistances.
03:51 At the point when amperage is zero, we can calculate the unknown resistance.
03:57 At the bottom of the yellow panel, a message appears.

It reads “Now the resistance can be calculated”.

04:06 Calculate resistance button is now active.
04:10 Click on the Calculate resistance button.
04:13 In the white coloured box the value of unknown resistance is displayed.
04:19 The measured value for Rx is 690 ohms. Here the value may change for you.
04:28 Click on the New measurement button for measuring the next set of values.
04:34 Again drag the sliding contact to zero.
04:38 Click on Calculate resistance button.
04:41 Observe the change in the value of unknown resistance.
04:44 This is because, galvanometer is a sensitive device.
04:50 It will change the value every time when we click on the New measurement button.
04:56 Press F5 key on the keyboard to restart the App.
05:01 Let us change the Comparable resistor to 1000 ohms.
05:06 Observe that Resistance of the meter changes to 10 ohms.
05:11 Now let us calculate the unknown resistance.
05:15 The formula to calculate the unknown resistance is,

Rx ={R2/R1} x R3

05:25 R1 and R2 are sliding resistance. R3 is the comparable resistance.
05:33 Change the Comparable resistance to 800 ohms and press Enter.
05:39 Again get the zero amperage by dragging the slider.
05:44 Now in the formula substitute value of R1 as 117.5 ohms, R2 as 82.5 ohms and R3 as 800 ohms.
05:57 Here the calculated value of unknown resistance in 561.7 ohms.
06:05 Here you can get a different value as the galvanometer is sensitive.
06:11 Now let us compare with the value shown in the App.
06:15 Click on the Calculate resistance button. Observe that the calculated value is comparable with the measured value.
06:24 As an assignment solve this numerical.
06:29 Let us explore the Potentiometer App.
06:33 Follow the same steps to open the App.
06:37 The interface opens with the potentiometer circuit.
06:42 The potentiometer is a voltage divider used for measuring voltage. It is also used to control the flow of current.
06:53 The circuit has three resistors.
06:56 Here two resistors are connected in series and used as a sliding resistor.
07:03 The third resistor is the Resistance of the appliance.
07:08 The voltmeter is connected in parallel to the resistance.
07:13 The voltmeter shows the output voltage of the circuit.
07:18 A scale is provided to take the measurement of voltage at that particular point.
07:25 The reading on scale is from 0.0 cm to 1.0 cm.
07:32 Drag the Position of the sliding contact to 0.4 cm.
07:38 The value of voltage at this point is 1.87 V(Volts).
07:44 Now increase the Resistance of the appliance to 1000 ohms.
07:49 Observe that the value of output voltage increased to 1.93 volts.
07:56 If we increase the value of potentiometer resistance, output voltage increases.
08:03 We can also calculate the voltage using the Ohm’s Law.
08:08 Check the check-box Indicate amperage.
08:12 Note that resistance till the point 0.4 cm is 39.5 ohms.
08:20 So we can calculate voltage using formula


08:27 I have already substituted the values of current and resistance from the App.
08:34 The value for voltage is almost same as that for measured value.
08:40 The graph is plotted for Voltage v/s length of the scale.
08:45 The blue point shows the value of voltage at point 0.4 cm.
08:52 Change the value of Sliding resistor to 1000 ohms and press Enter.
08:59 Observe that the value of current has decreased to 0.004 A.
09:07 So here we can say that potentiometer controls the flow of current.
09:13 Let us make a tabular column to study a graph of voltage v/s length.
09:19 Press F5 key on the keyboard to restart App.
09:24 Change the value of Voltage of the power supply to 10 V and press Enter.
09:31 Drag the sliding contact to 0.0 cm. The resistance and voltage at this point are zero.
09:41 Drag the sliding contact to 0.1 cm. Click on the Indicate amperage check box.
09:50 Tabulate the values of length, current and voltage in the tabular column.
09:56 Drag sliding contact to 0.2 cm and tabulate the values in the table.
10:04 Similarly take four more values and enter these values in the table.
10:10 Here is the completed table.
10:13 Observe that if length increases the output voltage also increases.
10:19 Hence the graph is linear.
10:23 As an assignment
10:25 Change the values of resistance of the appliance to 500 ohms, 700 ohms and 800 ohms.

Find the output voltage.

10:38 Let us summarise
10:40 In this tutorial we have,

Simulated the working of wheatstone bridge.

Solved a numerical based on wheatstone bridge.

Simulated the working of potentiometer

Solved numerical based on potentiometer

10:59 These Apps were created by Walter-fendt and his team.
11:04 The video at the following link summarizes the Spoken Tutorial project. Please download and watch it.
11:12 The Spoken Tutorial Project team,conducts workshops gives certificates. For more details, please write to us.
11:22 Please post your timed queries in this forum.
11:26 Spoken Tutorial Project is funded by MHRD, Government of India.
11:32 This is Himanshi Karwanje from IIT-Bombay. Thank you for joining.

Contributors and Content Editors

Pratik kamble