Physics Home > Teaching Labs > Electricity & Magnetism > Charges

Topics

Electrostatics, interactions of charged objects, Coulomb's law, charge distribution on conductors, vector superposition

Points of Emphasis

Electrostatic interactions of point charges and charge distributions, vector superposition

Prerequisites

Facility with free-body diagrams and a strong understanding of Newton's 2nd and 3rd laws.

Lab Activities

This lab provides an introduction to electrostatic and is divided into four sections.

Section I - Electrical Interactions. Students charge pieces of scotch tape in different ways and compare the interactions of the tapes with each other and with other objects at hand. Students are asked if their observations are consistent with idea that there are two types of charge.

Section II - Superposition. Students use Coulomb's law and Newton's 3rd law to compare forces exerted on various charges configurations involving two, three and four point charges. These are thought exercises. No experimental work is done in this section.

Section III - Distributed Charge. Students use a pith ball and acrylic rod to analyze the force on the pith ball by extended charge distributions.

Section IV - A Model for Electric Charge. Students look at the interaction between a charged and uncharged object

Course Level

Introductory level courses: Physics 4, Physics 14 and Physics 16.

Student Handouts

Faculty may see either David Abbott or Jan Largent for a copy of the write-up and the lab homework.

Equipment

Number of set-ups available: 20 Per lab station: 1 roll of scotch tape 1 18" wooden dowel 1 long metal bar 1 C-clamp 1 ring stand clamp 2 plastic rods 1 wool cloth 1 ruler 1 pith ball/string 1 metal coated pith ball/string

Notes

1. This lab exercise comes from Tutorials in Introductory Physics by Lillian C. McDermott, Peter S. Shaffer and the Physics Education Group, Department of Physics, University of Washington.
2. If the weather is rainy or humid, it helps to put dehumidifiers in the room while this lab is run.
3. If the air in the lab is dry, the wool cloths will work to generate charge on the black plastic rods. However, high humidity makes them ineffective. Animal fur seems to work well in both humid and dry conditions.

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Site contact: largent@Dartmouth.EDU

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