Ch 21electric Current & Direc Current Circuits

Subject

Electric Current

Resista nce and Ohm's Law Energy and Power in Electric Circuits

Relevant Equations

Relationships direct-current circuits: (DC circuits) the current always flows in the same direction. Alternating current circuits: (AC) Current periodically reverses their directions. •Batteries perform functions similar to an electric circuit. It I=(ΔQ/Δt) has two terminals one responding to high electric potential S.I.= C/s also energy and one to low electric potential energy. ampere, A •electromotive force or emf (E) of batter is the difference in Work done by electric potential between the terminals of a battery. Battery: •The direction of the current in an electrical circuit is the W=ΔQE direction in which a positive test charge would move. Ohm's Law: V=IR S.I.=Volts, V Resistivity: the quantity that characterizes the resistance of a 1ohm=(1V/A) given material •Resistance of a wire depends on its length Definition of and its area. Resistivity, ρ R=Δ(L/A) S.I= Ώ•m Potential Energy ΔU=(ΔQ)V Electrical Power P=IV S.I.= watt, W 1 kilowatt-hour = 3.6 x 106 J Series Parallel •Resistors are connected one after the other, end to end. Equivalent Resistance: Req = R1 + R2 + R3 + … = ΣR S.I. = Ohm,Ώ •Resistors are connected across the same potential difference. Equivalent Resistance: 1/Requiv = 1/R1 + 1/R2 + 1/R3 +…. = Σ1/R S.I. = Ohm, Ώ

Resistor s

Junction Rule Loop Rule •Current entering any point in a circuit must equal the current leaving that point. I1 = I1 - I1 or I1 - I2 - I3 =0. •The sum of all currents must equal 0. •The sum of all potential difference around any closed loop in a circuit is 0. E + ΔVCD = 0. |ΔVCD| = E = IR I = E/R

Kirchhof f's Rules Series Parallel Ceq = C1 + C2 + C3… = ΣC S.I. = Farad, F V1=Q/C1, Vn = Q/Cn 1/Ceq = 1/C1 + 1/C2 + 1/C3 +… Sigma 1/C

Capacit ors Ammete r and Voltmet er

ammeter: is connected in series with the section of the circuit where current is measured. Ideally, resistance is 0. Voltmeter: connected in parallel with the portion of circuit to be measured. Ideally, resistance is infinite.