Basic Electrometer

Experiment Samples

• Equal and Opposite Charge by Contact — The polarity indication of the Electrometer is most useful when showing that equal and opposite charges are produced by contact. The two different materials (on the ends of the wands held by the student) are rubbed together and the charges measured in the Faraday Ice Pail (ES-9042A). The Electrometer shows the charges are equal and opposite. If both materials are placed in the pail together, the net charge is zero.
• The Q=CV Relation — The Electrometer allows the student to measure the change in voltage across the capacitor plates as the separation is varied. Other experiments with the Basic Variable Capacitor (ES-9079) and Electrometer include:
  • Measuring the charge density on the plates as a function of voltage or plate separation.
  • Adding discrete amounts of charge to the plates (with a proof plane) and measuring the discrete increases in voltage. Q=CV can now be an experiment, not just a theory.
• Charge Distribution During Charge by Induction — Most students find it difficult to believe that on a conductive surface, the charge distribution can be uneven. In this experiment, a Sphere (ES-9059C) at 3000 V inductively charges an initially neutral sphere. At each step of the process, a Proof Plane (ES-9057C) is used to sample the charge at a certain location. The charge on the proof plane is then measured using the Faraday Ice Pail (ES-9042A) and Electrometer. Show the process, not just the results, of charge by induction.

Five Reasons to Use an Electrometer

• Quantitative Readout: The linear scale is a major advantage of the Electrometer. While an electroscope is only roughly quantitative, the Electrometer produces readings to ±3%. Verify physical laws and to determine if relations are linear or exponential. The Electrometer allows the student to measure rather than just observe.
• Direct Polarity Indication: Where polarity distinction is required, the electroscope is inconvenient; a known reference charge must be used. The Electrometer, by contrast, directly indicates polarity on a center-zero meter.
• Adjustable Sensitivity: The full scale sensitivity of the Electrometer is adjustable. Unlike the electroscope where the experiment must be adjusted to the measuring instrument, the Electrometer adjusts to the experiment.
• Large Display Capability: Although the unit is designed for small group use, the Electrometer may be connected easily (cable included) to a ScienceWorkshop Interface. With the use of DataStudio software, a meter display that fits the monitor can be produced.
• High Sensitivity: Increases the variety and scope of electrostatics demonstrations. Many electrostatics demonstrations theoretically possible with an electroscope are difficult because of the 100,000 VDC and higher voltages required. Such voltages are difficult to work with and hard to measure.

PASCO Electrometer Features

• Center-Zero Meter: Polarity is indicated directly.
• Switch-Selectable Ranges: 3, 10, 30 and 100 VDC. LED lights indicate the range in use.
• Zeroing Switch: Removes all charge from the input and brings the meter to zero.
• Automatic Shutoff: Turns off about 3 hours after turned on (or used in any way).
• Output Compatible with PASCO Interfaces: The interface cable included with the electrometer connects directly to an analog channel on a ScienceWorkshop interface, and connects to a PASPORT interface through a PS-2158 Analog Adapter. This enables the output signal from the electrometer to be recorded, displayed, and analyzed by the data acquisition software.
• Battery Operation: 4 “AA” cells included. Range indicator lights flash when batteries need to be replaced.