Apps-On-Physics/C3/Wheatstone's-Bridge-and-Potentiometer/English

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Visual Cue Narration
Slide Number 1

Title Slide

Welcome to the spoken tutorial on Wheatstone Bridge and Potentiometer.
Slide Number 2

Learning Objectives

At the end of this tutorial you will be able to
  • Simulate the working of wheatstone bridge.
  • Solve a numerical based on wheatstone bridge.
  • Simulate the working of potentiometer.
  • Solve a numerical based on potentiometer.
Slide Number 3

System Requirements

Here I am using,

Ubuntu Linux OS version 16.04

Firefox Web Browser version 62.0.3

Slide Number 4

Pre-requisites

https://spoken-tutorial.org/

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

For the Pre-requisites tutorials please visit this site.

Slide Number 5

Apps on Physics

In this tutorial we will use,

Wheatstone's Bridge and Potentiometer Apps.

Downloads folder>> html5phen>>phen>>

wheatstonebridge_en.htm file>> Right click >> open with Firefox web browser.

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

Select Open with Firefox Web Browser option.

Cursor on the interface. The App opens in the browser.
Point to the rectangle with Question mark(?) Wheatstone’s bridge is a simple circuit for measuring the unknown resistance.
Point to the circuit. Meter bridge uses the same principle for practical purposes.

First we will learn about the circuit connections.

Point to the four resistances. The circuit shows a simple series-parallel arrangement of resistances.
Point to voltage supply connections. The resistances are connected between the voltage supply and ground.
Point to the galvanometer. A galvanometer is connected between the two parallel branches of resistances.

Galvanometer is a device to detect small changes in current in the circuit.

Point to show the connection.

Point to the scale.

Drag the sliding contact show the changes.

The negative terminal of the galvanometer is connected to the wire of 1 cm.

The measurement of the wire is shown by the scale.

We can drag the sliding contact along the wire.

Point to show the sliding resistor. In the green panel the Sliding resistor is that of the wire.
Change the value in the text field and show. We can vary the Sliding resistor from 1 ohms to 1000 ohms.
Point to Comparable resistance. In the green panel we can also edit the values of Comparable resistor .

It is the standard resistance of the circuit.

In the green control panel point to Voltage of the power supply. Voltage of the power supply can take values from 1-10 Volts.

We can also change the Resistance of the meter.

Resistance of the meter depends on the comparable resistor.

Point to the check-box

Indicate voltage

Indicate amperage

At the bottom of control panel there are two check boxes.

Indicate voltage

Indicate amperage

Select both check-box.

Point to the values of voltage and current.

Select both the check-boxs.

Observe that the values of voltage and current are shown in the circuit.

Point to show the unkown resistance. We can calculate the unknown resistance when the bridge is balanced.
Cursor on the interface. Now let us see how to balance the bridge.
Press F5 key on the keyboard. Press F5 key on the keyboard to refresh the App.
Select Indicate voltage and Indicate amperage check-boxes. Click on Indicate voltage and Indicate amperage check-boxes.
Drag the sliding contact to get 0 amperage. To balance the bridge, drag the sliding contact to get a zero amperage.
Point to the slider Position of the sliding contact.

Also show by dragging the slider.

We can also drag the slider in the green panel to change the amperage.
Point the values of voltage. Observe the value of voltage and current at each resistances.

The values are balanced in series- parallel arrangement of resistances.

Point to the 0.00 mA.

At the bottom point to the white box at the bottom of the yellow panel.

At the point when amperage is zero we can calculate the unknown resistance.

At the bottom of the yellow panel, a message appears.

It reads “Now the resistance can be calculated”.

Point to Calculate resistance button. Calculate resistance button is now active.
Click on Calculate resistance button. Click on the Calculate resistance button.
Point to the value of Rx. In the white coloured box the value of unkown resistance is displayed.
Point to the Rx value The measured value for Rx is 908 ohms.

Here the value may change for you.

Click on the New measurement button. Click on the New measurement button for measuring the next set of values.
Drag the slider contact to zero. Again drag the sliding contact to zero.
Click on Calculate resistance button. Click on Calculate resistance button.
Point to the value. Observe the change in the value of unkown resistance.

This is because, galvanometer is a sensitive device.

It will change the value every time when we click on the New measurement button.

Press F5 key. Press F5 key on the keyboard to restart the App.
Edit the value of Comparable resistance to 1000 ohms and show the change in the Resistance of the meter. Let us change the Comparable resistor to 1000 ohms.

Observe that Resistance of the meter changes to 10 ohms.

Now let us calculate the unknown resistance.
Slide Number 6

Unknown Resistance

Rx={R2/R1}*R3

R1 and R2 is the sliding resistor.

R3 is the comparable resistance.

The formula to calculate the unknown resistance is,

Rx={R2/R1}*R3

R1 and R2 is the sliding resistor. R3 is the comparable resistance.

Click on New measurement button. Click on the New measurement button.
Edit the value of Comparable resistance to 800 ohms. And press Enter. Change the Comparable resistance to 800 ohms and press Enter.
Drag the Sliding contact to get zero ampere Again get the zero amperage by dragging the slider.
Show this in a text-box on the interface.

Point to the calculated value.

Now in the formula substitute the values of R1, R2, and R3.

Substitute the value of R1 as 93

R2 as 107 and R3 as 800 ohms.

Here the calculated value of unkown resistance in 816.16 ohms.

Here you can get a different value as the galvanometer is sensitive.

Now let us compare with the value shown in the App.
and then click on Calculate resistance. Click on the Calculate resistance button.

Observe that the calculated value is comparable with the measured value.

Slide Number 7

Assignment

In the circuit change the value of comparable resistance to 100 ohms and

sliding resistance to 65 ohms.

Calculate the unknown resistance of the circuit.

As an assignment solve this numerical.
Let us explore the Potentiometer App.
Directly open from the phen folder. Follow the same steps to open the App.
Point to the circuit The interface opens with the potentiometer circuit.

The potentiometer is a voltage divider used for measuring voltage.

It is also used to control the flow of current.

Point to the three resistors.

Point to the Sliding resistor.

The circuit has three resistors.

Here two resistors are connected in series and used as a sliding resistor.

Point to the 3rd resistor in the circuit. The third resistor is the Resistance of the appliance.
Point to the voltmeter. The voltmeter is connected in parallel to the resistance.

The volmeter shows the output voltage of the circuit.

Point to the scale. A scale is provided to take the measurement of voltage at that particular point.

The reading on scale is from 0.0 cm to 1.0 cm.

Drag the Position of the sliding contact to 0.4 cm Drag the Position of the sliding contact to 0.4 cm.
Point to the Voltmeter. The value of voltage at this point is 1.90 V(Volts).
Edit the value of Resistance of the appliance to 1000 Ohms. Now increase the Resistance of the appliance to 1000 ohms.
Point to the voltage in the voltmeter. Observe that the value of output voltage increased to 1.98 volts.
Cursor on the interface. If we increase the value of potentiometer resistance, output voltage increases.
We can also calculate the Voltage using the Ohm’s Law.
Click on the check-box of Indicate amperage. Check the check-box Indicate amperage.
Point to the value in the circuit. Note that resistance till the point 0.4 cm is 40 ohms.
Slide Number 8

Ohm’s Law

V=IR

=0.048 * 40

=1.942V

So we can calculate voltage using formula

V=IR

Substitute the value of current and resistance from the App.

The value for voltage is almost same as that for measured value.

Point to the the graph. The graph is plotted for Voltage v/s length of the scale.
Point to the blue point in the graph. The blue point shows the value of voltage at point 0.4 cm.
Edit the value of Sliding resistor to 1000 Ohms in the control panel.

Press Enter.

Change the value of Sliding resistor to 1000 ohms and press Enter.
Point to the value of current. Observe that the value of current has decreased to 0.003 A.
Cursor on the interface. So here we can say that potentiometer controls the flow of current.
Slide Number 9

Tabular column

Let us make a tabular column to study a graph of voltage v/s length.
Press F5 key on the keyboard. Press F5 key on the keyboard to restart App.
Edit the Voltage of the power supply to 10 V. And Press Enter. Change the value of Voltage of the power supply to 10 V and press Enter.
Drag the Sliding contact to 0.0 cm. Drag the sliding contact to 0.0 cm.
Point to the value of resistance and voltage. The resistance and voltage at this point are zero.
Drag the Sliding contact to 0.1 cm. Drag the sliding contact to 0.1 cm.
Point to value of length, current, and voltage. Tabulate the values of length, current and voltage in the tabular column.
Drag it to 0.2 cm Drag sliding contact to 0.2 cm and tabulate the values in the table.

Smilarly take four more values and enter these values in the table.

Slide Number 10

Tabular column

Here is the completed table.

Observe that if length increases the output voltage also increases.

Hence the graph is linear.

Slide Number 11

Assignment

Change the values of Resistance of the appliance to 500 ohms, 700 ohms, 800 ohms.

Find the output voltage.

As an assignment

Change the values of Resistance of the appliance to 500 ohms, 700 ohms, 800 ohms.

Find the output voltage.

Let us summarise
Slide Number 12

Summary

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.
Slide Number 13

About Spoken Tutorial project.

The video at the following link summarizes the Spoken Tutorial project.

Please download and watch it.

Slide Number 14

Spoken Tutorial workshops.

The Spoken Tutorial Project team,

conducts workshops gives certificates.

For more details, please write to us.

Slide Number 15

Forum for specific questions:

Please post your timed queries in this forum.
Slide Number 16

Acknowledgement

Spoken Tutorial Project is funded by MHRD, Government of India.
This is Himanshi Karwanje from IIT-Bombay.

Thank you for joining.

Contributors and Content Editors

Karwanjehimanshi95, Madhurig, Snehalathak

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