Download Series and parallel circuits (S8P5b)

Series and Parallel Circuits
GPS: S8P5b –Demonstrate the advantages and disadvantages of series and
parallel circuits and how they transfer energy.
Textbook reference: page 201
Lecture notes:
Series and parallel circuits (S8P5b)
House wiring is done in an arrangement known as a parallel circuit.
Another common type of circuit is called a series circuit.
To understand the difference between the two, imagine a string of Christmas lights:
some strings have the property of being able to light with a dead bulb and some are
not able to light with a dead bulb.
Explain
In this case the bulbs are a type of resistance.
Characteristics of series circuits: 1 path for current
1. current is the same everywhere (ammeter operation)
IT = I1 = I2 =I3
2. voltage is different across different resistances
VT = V1 + V2 + V3 (voltmeter operation)
3. total resistance is equal to the sum of the resistances
R = R1 + R2 + R3
4. a break in the circuit stops all current
VIR triangle =
3 resistors of 60, 30 and 20 ohms are connected in series across a 90 V
difference in potential.
Find the equivalent resistance of the circuit. (110 ohm)
Find the current in the entire circuit. (.8181 A)
Find the current through each resistor. (.8181 A)
Characteristics of parallel circuits: more than 1 path for current
1. current is different in different resistances, but the total current is equal to
the sum of the currents in all the branches
IT = I1 + I2 + I3
2. voltage is the same across all resistances
VT = V1 = V2 =V3
3. total resistance is less than the sum of the individual resistances
VT/RT = V1/R1 +V2/R2 + V3/R3
1/RT = 1/R1 + 1/R2 + 1/R3
4. a break in the circuit only stops current in the branch where the break occurs
3 resistors of 60, 30 and 20 ohms are connected in parallel across a 90 V
difference in potential.
Find the equivalent resistance of the circuit. (10 ohm)
Find the current in the entire circuit. (9 A)
Find the current through each branch of the circuit. (1.5 A, 3 A, 4.5 A)
Series-parallel circuits:
Many circuits are a combination of some components in series and some in
parallel.
The key to analyzing a series-parallel circuit is to convert it into an equivalent
series circuit.
Homework: Electric circuit problems (Course Schedule, see scan for solutions to
problems 1 and 2.)