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