Charge Produced by Induction

Figure 1

In this experiment you will charge a pair of conductive spheres by induction and then measure the charge on each sphere.

In the induction process, a charged object is brought near to a neutral conducting object without touching the two objects together. In this case, we will use two connected conductive cylinders as our neutral object. The presence of a charged object near a neutral conductor will force (or induce) electrons within the conductor to move. The movement of electrons leaves an imbalance of charge on opposite sides of the neutral conductor.

While overall the object is neutral (i.e. has the same number of electrons as protons), there is an excess of positive charge on one cylinder and an excess of negative charge on the other cylinder. Once the cylinders have been separated, each one is left with a net charge.

einstein™Tablet+ with MiLAB or Android/iOS Tablet with MiLAB and einstein™LabMate Electrostatic Charge sensor Test leads with BNC connector Faraday ice pail Two conductive spheres on an insulated stand (each sphere's diameter must be smaller than the diameter of the Faraday ice pail inner cylinder) PVC plastic strip or pipe A piece of woolen cloth

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Launch MiLAB ( ).

Connect the Electrostatic Charge sensor to one of the ports on the einstein™Tablet+ or einstein™LabMate.

Connect the test leads to the Electrostatic Charge sensor.

Assemble the equipment as shown in Figure 1. a. Connect the red lead to the inner cylinder of the Faraday ice pail. b. Connect the black lead to the outer cylinder of the Faraday ice pail.

Make sure that only the Charge sensor is selected.

Note: You may need to ground the outer cylinder of the Faraday ice pail.

Program the sensor to log data according to the following setup: Electrostatic Charge Sensor

Charge, 25 nC (nC)

Set As Zero

ON

Rate:

10/sec

Duration:

2 Min

1.

Bring the two conductive spheres into contact (see Figure 2).

Figure 2 2.

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Rub the PVC strip with the woolen cloth to charge it.

Bring the PVC strip near one sphere but don’t touch it.

With the PVC strip still near one sphere hold the insulating rod of the other sphere and move it away to separate the spheres.

5.

Short circuit the two leads of the Electrostatic charge sensor. To short circuit the sensor, connect the positive (red) and negative (black) leads.

6.

Tap Run (

7.

Hold the sphere that was nearest to the PVC rod by its insulating rod and insert it into the lower half of the inner cylinder of the pail, while not letting it touch the pail.

8.

Tap Stop (

) to stop collecting data.

9.

Tap Save (

) to save your data.

) to begin recording data.

10. Remove the sphere.

11. Short circuit the two leads of the Electrostatic charge sensor.

12. Now repeat steps ‎6 to ‎10, inserting the other sphere into the pail and recording the readings.

1. What happens when you rub a piece of PVC plastic with a woolen cloth?

2. Explain how the spheres were charged.

3. Were the two spheres charged equally and opposite, when you measured them? Explain.

Use your measurements to determine the sign of the charge on the PVC strip. Explain.