DC Circuits

Study Guide for Chapters 27 and 28

It is likely that there will be a DC circuit question on the exam. I recommend studying the following two

topics:

The relationship between energy and power.

Resistors in series and in parallel (including complicated arrangements).

Kirchhoff's laws be required for the final exam.will not

Chapter 27: Current and Resistance

Electric current magnitude is the flow of electric charge. The of the current is the charge per

unit time that flows through the conductor:

M œ

U

>?

A is a circuit element that opposes the flow of electric current. When current flowsresistor

through a resistor, the result is a potential difference in the opposite direction:

Z œ MV

Here is the potential difference, is the current through the resistor, and is the .Z M V resistance

A forces current through a circuit by maintaining a constant potential difference acrossbattery

its leads. A battery adds energy to a circuit:

c œ MZ

Here is the the amount of energy delivered per unit time. Power is measured inc power

watts, which are joules per second.

A resistor dissipates energy from the circuit:

c œ MZ œ M V œ

Z

V

#

#

In this equation represents the amount of energy dissipated per unit time:c

c

?

?

œ

>

a benergy

Problems:Chapter 27 # 1, 23, 27

Chapter 28: DC Circuits

When two resistors are in , their resistances :series add

V œ V V

total"#

When two resistors are in , the addition works diff erently:parallel

V œ

"

total

""

V V

"#

These rules can be combined to analyze more complic ated arrangements of resistors:

V œ V V

"

total"'

""

V V V V

#$ % &

When these rules can be applied, they are much easier to use than Kirchhoff's laws.

The following problems all involve series and paral lel resistors. Do use Kirchhoff's laws tonot

solve these problems.

Problems:Chapter 28 # 5, 7, 9, 15

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