Electric Circuits
Objectives Distinguish between series and
parallel connections Calculate the current, voltage, and
equivalent resistance for devices connected in series and parallel
Construct a voltage divider Describe the features of a multi-
meter and explain how to use it in a circuit
Electric Circuit Components
Capacitor Stores charge Creates a potential difference Source of energy
Resistor “Opposes” current (charge flow) “Uses” potential difference Dissipates energy
Electric Circuits
Electric current requires two conditions A “closed” circuit, or
complete path for charges to flow
A potential difference, or voltage source (usually a cell or battery)
Electric Circuits
Two types of electric circuits Series (only one current path) Parallel (more than one current path,
i.e. “branches”)
Equivalent Resistance
Series resistors Resistors in series add together
R R R R Req n 1 2 3
Current
The current through a circuit component is equal to the voltage divided by the resistance
RV
IIV
R
Textbook, Pg. 533
Voltage
The voltage “drop” or potential difference across a circuit component equals the product of the current and the resistance
RV
IV IR
Textbook, Pg. 534
Voltage Divider
Series circuit used to produce a voltage source of desired magnitude from a higher-voltage battery
Textbook, Pg. 535
Practice Problems
Textbook, Page 534 #1 – 5 Textbook, Page 536 – 537
(Examples) Textbook, Page 537 #6 – 9
Equivalent Resistance
Parallel resistors Resistors in parallel
add together as the reciprocals
Hint: Remember to invert the sum to find Req
1 1 1 1 1
1 2 3R R R R Req n
Textbook, Pg. 539
Kirchoff’s Laws
Voltage Conservation
of energy Current
Conservation of charge
Conservation of Energy
The sum of potential “drops” or voltages in a circuit equals the source
In a series circuit, all the voltages add up to equal the source
In a parallel circuit, the voltage applied to each branch is equal to the source
Conservation of Charge The sum of all currents in a circuit
is equal to the current leaving the source
In a series circuit, the current is the same at every point
In a parallel circuit, the sum of all currents entering any junction is the same as the sum of all currents leaving the junction
Series-Parallel Circuit
What is the voltage drop across each resistor and the current flowing through them?
Practice Problems
Textbook, Page 540 #10 – 12 Textbook, Page 547 #13
Measurements Voltmeter
Measures potential difference (volts) DVM (digital voltmeter)
Ammeter Measures current (amps) Galvanometer (very sensitive ammeter)
Ohm-meter Measures resistance (ohms)
Multimeter Measures all three
Measurements
Voltmeter Parallel
Ammeter Series
Ohm-meter Disconnect power Isolate resistor
from circuitTextbook, Pg.
547