Chapter 28: Fundamentals of Circuits

Suppose you have resistors $2.5\mathrm{k}\Omega$, $3.5\mathrm{k}\Omega$and $4.5\mathrm{k}\Omega$ and a $100\mathrm{V}$ power supply. What is the ratio of the total power delivered to the resistors if they are connected in parallel to the total power delivered if they are connected in series?

a. What are the magnitude and direction of the current in the $18\Omega$resistor in FIGURE $EX28.5$?

b. Draw a graph of the potential as a function of the distance traveled through the circuit, traveling cw from $V=0V$at the lower left corner.

The circuit of FIGURE has two resistors, with $R_1>R_2$. Which of the two resistors dissipates the larger amount of power? Explain.

A lightbulb is in series with a $2.0\Omega$resistor. The lightbulb dissipates $10\mathrm{W}$ when this series circuit is connected to a $9.0\mathrm{V}$ battery. What is the current through the lightbulb? There are two possible answers; give both of them.

A. Load resistor R is attached to a battery of emf E and internal resistance r. For what value of the resistance R, in terms of E and r, will the power dissipated by the load resistor be a maximum?

B. What is the maximum power that the load can dissipate if the battery has $\mathrm{E}=9.0\mathrm{V}$and localid="1649415601268" $\mathrm{r}=1.0\Omega$?

The ammeter in FIGURE P28.52 reads$3.0\mathrm{A}$. Find ${\mathrm{I}}_1,{\mathrm{I}}_2,$and $\mathrm{\epsilon }.$

What is the current in the$2\Omega$resistor in FIGURE P28.53?

For an ideal battery$(\mathrm{r}=0)$, closing the switch in FIGURE P28.54 does not affect the brightness of bulb A. In practice, bulb A dims just a little when the switch closes. To see why, assume that the$1.50\mathrm{V}$battery has an internal resistance$\mathrm{r}=0.50\Omega$and that the resistance of a glowing bulb is$\mathrm{R}=6.00\Omega$.

a. What is the current through bulb A when the switch is open?

b. What is the current through bulb A after the switch has closed?

c. By what percentage does the current through A change when the switch is closed?

What are the battery current ${\mathrm{I}}_{\mathrm{bat}}$and the potential difference ${\mathrm{V}}_{\mathrm{a}}-{\mathrm{V}}_{\mathrm{b}}$between points a and b when the switch in FIGURE P28.55 is (a) open and (b) closed?

A battery is a voltage source, always providing the same potential difference regardless of the current. It is possible to make a current source that always provides the same current regardless of the potential difference. The circuit in FIGURE P28.56 is called a current divider. It sends a fraction of the source current to the load. Find an expression for ${\mathrm{I}}_{\mathrm{load}}$in terms of ${\mathrm{R}}_1,{\mathrm{R}}_2$and ${\mathrm{I}}_{\mathrm{source}}.$You can assume that the load’s resistance is much less than${\mathrm{R}}_2.$