Calculations in Fundamental Physics

Electricity and Magnetism

T. Heddle, Robert Robinson, N. Hiller, Robert Robinson, N. Hiller

• Publisher: Pergamon
• Year: 2013
• ISBN:
  9781483137919
• Topic: Naturwissenschaften
• Subtopic: Energie

Calculations in Fundamental Physics, Volume II: Electricity and Magnetism focuses on the processes, methodologies, and approaches involved in electricity and magnetism. The manuscript first takes a look at current and potential difference, including flow of charge, parallel conductors, ammeters, electromotive force and potential difference, and voltmeters. The book then discusses resistance, networks, power, resistivity and temperature, and electrolysis. Topics include shunts and multipliers, resistors in series, distribution circuits, balanced potentiometers, heating, resistance thermometry, and thermistors. The text explains electrolysis and thermoelectricity, including electroplating, Avogadro's number, and thermoelectric power. The manuscript describes magnetic fields and circuits and inductors. Concerns include straight conductors, series circuits, magnetic moments, stored energy, and mutual inductance. The book also takes a look at electric fields, transients, and direct current generators and motors. The manuscript is a dependable reference for readers wanting to be familiar with electricity and magnetism.

CHAPTER 1

CURRENT AND POTENTIAL DIFFERENCE

Publisher Summary

Two types of charged particles are involved in the structure of any material—the positively charged nuclei of the atoms and the negatively charged electrons moving around the nuclei. When no current flows in a stationary conductor, the continual orbiting and jostling of these particles lead to no resultant large-scale movement of either positive or negative charge one way or another. If an electric cell is connected in a closed circuit of conductors, the cell tends to drive negative particles one way around the circuit and positive the other. The direction of flow of the positive charge is the direction of the current. In most solid conductors, electric currents consist only of those electrons that are free to drift through the solid, while the positive nuclei, with orbiting electrons, remain localized in the solid structure. Many effects of currents are the same whether because of positive particles drifting in one direction or to negative in the other. When an electric current flows in a wire, a magnetic field is produced in the surrounding space or medium. Evidence of this field is provided by the force exerted on a magnetic compass or on another conductor carrying a current. Such a force can be attributed to the existence of magnetic flux, which is imagined to pass around the current causing the field, and to have the same direction as a compass needle.

Flow of Charge

1.1 WORKED EXAMPLE

Two lamps are connected in parallel across a battery of cells. A current of 1.6 A flows through the battery when the current through one lamp is 7.5×10¹⁸ electrons per second. Calculate the current through the second lamp (a) in amperes, and (b) in electrons per second.

Introduction

Two types of charged particles are involved in the structure of any material: the positively charged nuclei of the atoms and the negatively charged electrons moving around the nuclei. When no current flows in a stationary conductor, the continual orbiting and jostling of these particles leads to no resultant large scale movement of either positive or negative charge one way or another. If, however, an electric cell is connected in a closed circuit of conductors, the cell tends to drive negative particles one way around the circuit and positive the other. The direction of flow of the positive charge is said to be the direction of the current. Yet in most solid conductors, electric currents consist only of those electrons which are free to drift through the solid, while the positive nuclei, with orbiting electrons, remain localized in the solid structure.

Many effects of currents are the same whether due to positive particles drifting in one direction or to negative in the other. Also the magnitudes of currents are more easily measured by their effects than by attempting to count the numbers or rates of flow of the particles. Thus the unit of current, the ampere (A), is determined by a convenient effect, namely the force exerted between parallel wires carrying currents (as inFig. 1.1). The ampere is that constant current which, i...