Chapter 28: Fundamentals of Circuits

In FIGURE EX28.31, what is the value of the potential at points $a\mathrm{and}b$?

Show that the product RC has units of s.

What is the time constant for the discharge of the capacitors in FIGURE EX28.33?

What is the time constant for the discharge of the capacitors in FIGURE EX28.34?

A $10\mu F$capacitor initially charged to $20\mu C$is discharged through a $1.0k\Omega$ resistor. How long does it take to reduce the capacitor’s charge to $10\mu C$?

The switch in FIGURE EX28.36 has been in position a for a long time. It is changed to position b at$t=0$ . What are the charge $Q$on the capacitor and the current $I$through the resistor $\left(a\right)$immediately after the switch is closed? $\left(b\right)$at$t=50\mu s$ ? $\left(c\right)$at $t=200\mu s$?

What value resistor will discharge a $1.0\mu F$capacitor to $10\%$ of its initial charge in $2.0ms$?

A capacitor is discharged through a $100\Omega$resistor. The discharge current decreases to $25\%$ of its initial value in $2.5ms$. What is the value of the capacitor?

It seems hard to justify spending $\backslash (4.00$for a compact fluorescent lightbulb when an ordinary incandescent bulb costs $50¢$. To see if this makes sense, compare a $60\mathrm{W}$incandescent bulb lasting $1000$hours to a $15\mathrm{W}$compact fluorescent bulb having a lifetime of $10,000$hours. Both bulbs produce the same amount of visible light and are interchangeable. If electricity costs $\backslash )0.10/\mathrm{kWh}$, what is the total cost—purchase plus energy— to obtain$10,000$ hours of light from each type of bulb? This is called the life-cycle cost.

The circuit of FIGURE Q28.4 has two resistors, with $R_1>R_2$. Which of the two resistors dissipates the larger amount of power? Explain.