91Ó°ÊÓ

A typical American family uses $1000kWh$of electricity a month.

a. What is the average current in the $120V$power line to the house?

b. On average, what is the resistance of a household?

A waterbed heater uses $450W$of power. It is on $25\%$of the time, off $75\%$. What is the annual cost of electricity at a billing rate of $\$0.12/kWh$?

What is the value of resistor $R$in FIGURE $EX28.16$?

The battery in FIGURE $EX28.17$is short-circuited by an ideal ammeter having zero resistance.

a. What is the battery’s internal resistance?

b. How much power is dissipated inside the battery?

The circuit in FIGURE $EX28.18$is called a voltage divider. What value of $R$will make $V_{out}=V_{in}/10$?

The voltage across the terminals of a $9.0V$battery is $8.5V$ when the battery is connected to a $20\mathrm{Î\copyright }$ load. What is the battery’s internal resistance?

Draw a circuit diagram for the circuit of FIGURE EX28.2

The tip of a flashlight bulb is touching the top of the $3V$battery in FIGURE Q28.2. Does the bulb light? Why or why not?

Compared to an ideal battery, by what percentage does the battery’s internal resistance reduce the potential difference across the $20\mathrm{Î\copyright }$resistor in FIGURE EX28.20?

A variable resistor $R$is connected across the terminals of a battery. FIGURE EX28.21 shows the current in the circuit as $R$is varied. What are the emf and internal resistance of the battery?