Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8EE201 Lecture 1 P. 1Charge, Current, Circuit elementsCharge++++ +++++++ +++FFGlass rods rubbed with silk repel each otherGlass - Glass RepulsionLucite - Lucite RepulsionGlass - Lucite AttractionCharge on glass: ‘Positive’Charge on lucite: ‘Negative’EE201 Lecture 1 P. 2Empirical Observation:Similar charges repel; Opposite charges attractAtomic theoryCharge is an electrical property of matter.Electrons: negative; Protons: positive Basic unit of charge: Coulomb (C)Charge of proton = 1.602 x 10-19 CCharge of electron = -1.602 x 10-19 CNotation for chargeQ -- fixed in timeq or q(t) -- time dependentEE201 Lecture 1 P. 3+ +FForce on unit charge gives rise to Charge in motionField around test chargeEssence of course: Learning how to control chargeControl is achieved using circuitsSimple circuit elements include sources, resistors, capacitors, inductors, and operational amplifiers.EE201 Lecture 1 P. 4CurrentThe net flow of charge across any area of matter constitutes a current through the area.Basic unit of current: Ampere (A) 1 Ampere equals the net movement of 1 C of charge per second. 1A = 1C/secConvention The direction of current flow is in a direction opposite to the flow of electrons, or along the flow of positive charges.Examples using generalized circuit elements:currentnegative chargescurrentpositive chargesEE201 Lecture 1 P. 5Note: current can be positive or negative.Current flow is easy through conductors.Metals are good conductors.Current flow is difficult through insulators.Ceramics are good insulators.ExampleIn 1 sec, 6.24 x 1017 electrons pass from left to right through the left end of the copper wire shown.(a) What direction does the current flow?(b) What is the magnitude of the current? e-Cu wireEE201 Lecture 1 P. 6Solution(a) Current flows from right to left(b) Charge of electron = -1.602 x 10-19 C, or-1 C = charge of 6.24 x 1018 electronx A = x C/sec6.24 x 1017 electrons = -0.1 CTherefore, current = -0.1 A (L to R)0.1 A (R to L)If a net charge q crosses a boundary in t sec, then,I = q / twhere I denotes a constant current that is independent of time.EE201 Lecture 1 P. 7The instantaneous, or time dependent, current isi(t) = dq(t) / dtwhere q(t) is the amount of charge crossing a boundary in interval (to, t). The integral form of this equation is,t q(t) = i(t) dt -Current that is constant with time is called direct current (dc). Current that varies sinusoidally with time is calledalternating current (ac). i(t) = A sin(t + ) where A is the amplitude of the sin wave, is the angular frequency, and is the phase angle.EE201 Lecture 1 P. 8Examplei(t) At (sec)246-22 4 6 8 10For the time-dependent current shown, find the charge transferred through a wire over the time intervals (a) 0 t 4s and, (b) 0 t 10s .wireSolutiont q(t) = i(t) dt to(a) By inspection, q(t) = 12 C(b) q(t) = 12 C - 8 C = 4
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