1. Work in Electrical Systems
Chapter 2 Section 3
Work in Electrical Systems

2. Objectives
Explain the relationship between work, charge and potential difference (voltage).
Calculate electrical charge in a circuit.
Define units of electric current.
Solve problems in electrical work.
Identify effects of electrical work.
Explain efficiency in terms of work in and work out in electrical systems.

3. Coulombs The unit of electric charge is the coulomb (C).
The fundamental charge on an electron is 1.6 X C.
1 C = 1/ 1.6 X = 6.25 X 1018 electrons or 6,250,000,000,000,000,000 electrons.

4. Work in electrical systems
The electric field is given by E = F / q (Sec 1.3). Thus F=Eq.
Potential difference (voltage) is given by V=Ed (Sec 1.3)
W = Fd = Eqd
Thus W = Vq

5. Work - cont Thus Work = potential difference X charge moved W=Vq
The work needed to move one coulomb of charge though a potential difference of one volt is one joule.
1J = 1 V . C
1V = 1 J/C

6. Electric Charge & Current
Electric current is the rate at which charge flows through a circuit.
Current = charge / time; I = q / t
Current is measured in amperes or amps (A)
1 amp = 1 coulomb per second; A = 1 C/s

7. Efficiency Efficiency = work out / work in; Wout / Win
% Efficiency = (Wout / Win) x 100%
Efficiency can never be equal to or greater than 100%
Work out will always be less than work in.

8. Summary
Electric work is done when a charge is moved through a potential difference.
W = Vq
1 joule = 1 volt X 1 coulomb; 1J = 1V.C
Current is the rate at which charge flows.
1 Amp = 1 coulomb per second; 1A=1C/s.
% Efficiency = (Wout / Win) x 100%