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Transcript
Chapter 2 Section 3 Work in Electrical Systems 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. Coulombs • The unit of electric charge is the coulomb (C). • The fundamental charge on an electron is 1.6 X 10-19 C. • 1 C = 1/ 1.6 X 10-19 = 6.25 X 1018 electrons or 6,250,000,000,000,000,000 electrons. 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 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 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; 1A = 1 C/s 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. 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%
