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Unformatted text preview: 1 Basic Concepts 1.1 1.2 1.3 1.4 1.5 1.6 Systems of Units. Electric Charge. Current. Voltage. Power and Energy. Circuit Elements. Dr Dr Branislav Hredzak Alexander and Sadiku, Fundamentals of Electric Circuits, Third Edition. McGraw-Hill 2 System of Units (1) Six basic units Dr Dr Branislav Hredzak Alexander and Sadiku, Fundamentals of Electric Circuits, Third Edition. McGraw-Hill 3 System of Units (2) The derived units commonly used in electric circuit theory Dr Dr Branislav Hredzak Alexander and Sadiku, Fundamentals of Electric Circuits, Third Edition. McGraw-Hill 4 System of Units (2) Decimal multiples and submultiples of SI units Dr Dr Branislav Hredzak Alexander and Sadiku, Fundamentals of Electric Circuits, Third Edition. McGraw-Hill 5 Electric Charges (1) • Charge is an electrical property of the atomic particles of which matter consists, measured in coulombs (C). • The charge e on one electron is negative and equal in magnitude to 1.602 × 10-19 C which is called as electronic charge. The charges that occur in nature are integral multiples of the electronic charge. Dr Dr Branislav Hredzak Alexander and Sadiku, Fundamentals of Electric Circuits, Third Edition. McGraw-Hill 6 Electric Charges (2) • When a wire is connected to a battery, positive charges move in one direction while negative charge move in the opposite direction • It is conventional to take the current flow as the movement of positive charges Dr Dr Branislav Hredzak Alexander and Sadiku, Fundamentals of Electric Circuits, Third Edition. McGraw-Hill 7 Current (1) • Electric current is the time rate of change of charge, measured in amperes (A) • Mathematically: Electric current i = dq/dt. The unit of ampere can be derived as 1 A = 1C/s. • A direct current (dc) is a current that remains constant with time. • An alternating current (ac) is a current that varies sinusoidally with time. (reverse direction) Dr Dr Branislav Hredzak Alexander and Sadiku, Fundamentals of Electric Circuits, Third Edition. McGraw-Hill 8 Current (2) • The direction of current flow Positive ions Negative ions Dr Dr Branislav Hredzak Alexander and Sadiku, Fundamentals of Electric Circuits, Third Edition. McGraw-Hill 9 Current (3) Example 1 A conductor has a constant current of 5 A. How many electrons pass a fixed point on the conductor in one minute? Dr Dr Branislav Hredzak Alexander and Sadiku, Fundamentals of Electric Circuits, Third Edition. McGraw-Hill 10 Current (4) Solution Total no. of charges that pass in 1 min is given by Total no. of electrons that pass in 1 min is given Dr Dr Branislav Hredzak Alexander and Sadiku, Fundamentals of Electric Circuits, Third Edition. McGraw-Hill 11 Voltage (1) • Voltage (or potential difference) is the energy required to move a unit charge through an element, measured in volts (V). • Mathematically, v ab = dw dq (volt) – w is energy in joules (J) and q is charge in coulomb (C). • Electric voltage, vab, is always across the circuit element or between two points in a circuit. – vab > 0 means the potential of a is higher than potential of b. – vab < 0 means the potential of a is lower than potential of b. Dr Dr Branislav Hredzak Alexander and Sadiku, Fundamentals of Electric Circuits, Third Edition. McGraw-Hill Power and Energy (1) 12 • Power is the time rate of expending or absorbing energy, measured in watts (W). • Mathematical expression: dw dw dq p= = ⋅ = vi dt dq dt i i + + v v – – Passive sign convention P = +vi absorbing power p = –vi supplying power Dr Dr Branislav Hredzak Alexander and Sadiku, Fundamentals of Electric Circuits, Third Edition. McGraw-Hill Power and Energy (2) 13 • The law of conservation of energy ∑p=0 • Energy is the capacity to do work, measured in joules (J). • Mathematical expression t t t0 t0 w = ∫ pdt = ∫ vidt Dr Dr Branislav Hredzak Alexander and Sadiku, Fundamentals of Electric Circuits, Third Edition. McGraw-Hill 14 Circuit Elements (1) Active Elements Passive Elements • A dependent source is an active element in which the source quantity is controlled by another voltage or current. Independent Dependant sources sources • There are four different types: VCVS, CCVS, VCCS, CCCS. Dr Dr Branislav Hredzak Alexander and Sadiku, Fundamentals of Electric Circuits, Third Edition. McGraw-Hill ...
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