Electric Fields and Capacitors Chapter 3 Learning Outcomes This chapter deals with the laws and properties of electric ﬁ elds and their application to electric components known as capacitors. On completion of this chapter you should be able to: 1 Understand the properties of electric ﬁ elds and insulating materials. 2 Carry out simple calculations involving these properties. 3 Carry out simple calculations concerning capacitors, and capacitors connected in series, parallel and series/parallel combinations. 4 Describe the construction and electrical properties of the different types of capacitor. 5 Understand the concept of energy storage in an electric ﬁ eld, and perform simple related calculations.75 3.1 Coulomb ’ s Law A force exists between charged bodies. A force of attraction exists between opposite charges and a force of repulsion between like polarity charges. Coulomb ’ s law states that the force is directly proportional to the product of the charges and is inversely proportional to the square of the distance between their centres. So for the two bodies shown in Fig. 3.1 , this would be expressed as FQQd122 In order to obtain a value for the force, a constant of proportionality must be introduced. In this case it is the permittivity of free space, 0 . This concept of permittivity is dealt with later in this chapter, and need not concern you for the time being. The expression for the force in newtons becomes