Electric Circuits PDF

Chapter 18 Electric Circuits  Ohm’s Law In a conductor, the voltage applied across the ends of the conductor is proportional to the current through the conductor. The constant of proportionality is the resistance of the conductor. Units of resistance are ohms (Ω) ...

Chapter 18 Electric Circuits  Ohm’s Law In a conductor, the voltage applied across the ends of the conductor is proportional to the current through the conductor. The constant of proportionality is the resistance of the conductor. Units of resistance are ohms (Ω)  Resistors in Series When two or more resistors are connected end-to- end, they are said to be in series. The current is the same in all resistors because any charge that flows through one resistor flows through the other. The sum of the potential differences across the resistors is equal to the total potential difference across the combination. 1 2 1 2 A B  Resistors in Series, Cont. Potentials add – ΔV = IR1 + IR2 = I (R1+R2) – Consequence of Conservation of Energy The equivalent resistance has the effect on the circuit as the original combination of resistors. Section 18.2 In series: 1.Current is the same, 2.Voltage is the sum of the voltage of the individual resistors In series: 1.Current is the same, 2.Voltage is the sum of the voltage of the individual resistors 3.Total resistance is the sum of the resistance of the individual resistors.  Equivalent Resistance – Series Req = R1 + R2 + R3 + … The equivalent resistance of a series combination of resistors is the algebraic sum of the individual resistances and is always greater than any of the individual resistors. If one element in the series circuit fails, the circuit would no longer be complete and none of the elements would work. Section 18.2  Equivalent Resistance – Parallel Equivalent Resistance The inverse of the equivalent resistance of two or more resistors connected in parallel is the 18V algebraic sum of the inverses of the individual resistance. – The equivalent is always less than the smallest resistor in the group. Series combination Parallel combination 1. Current is the same 2. Total voltage is the sum of the voltage of the individual resistors 3. Equivalent resistance is the sum of the resistance of the individual resistors 1 A 2 parallel 1 2 B 1 2 1 2 series A B Example Complex circuit 4V, 0.67A reduction 2A 8V 16V 4V, 1.33A 24V 4V 2A 2A 2A 28V Section 18.3  Activity Find the equivalent resistance, and voltage across 250Ω  Activity (a) Find the equivalent resistance between points a and b in the Figure. (b) Calculate the current in 4 and 9 resistors if a potential difference of 34 V is applied between a and b.  Activity Find the current through 4ohm resistor