Chapter 28: Fundamentals of Circuits

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.

A refrigerator has a $1000\mathrm{W}$compressor, but the compressor runs only $20\%$of the time.

a. If electricity costs$\backslash (0.10/\mathrm{kWh}$, what is the monthly (30 day) cost of running the refrigerator?

b. A more energy-efficient refrigerator with an $800\mathrm{W}$ compressor costs$\backslash )100$ more. If you buy the more expensive refrigerator, how many months will it take to recover your additional cost?

Two $75\mathrm{W}(120\mathrm{V})$ lightbulbs are wired in series, then the combination is connected to a $120\mathrm{V}$ supply. How much power is dissipated by each bulb?

An electric eel develops a $450\mathrm{V}$potential difference between its head and tail. The eel can stun a fish or other prey by using this potential difference to drive a $0.80\mathrm{A}$current pulse for $1.0\mathrm{ms}$. What are

(a) the energy delivered by this pulse and

(b) the total charge that flows?

You have a $2.0\Omega$resistor, a $3.0\Omega$resistor, a $6.0\Omega$resistor, and a $6.0\mathrm{V}$battery. Draw a diagram of a circuit in which all three resistors are used and the battery delivers 9.0 W of power.

A $2.0\mathrm{m}$long, $1\mathrm{mm}$diameter wire has a variable resistivity given by

localid="1649324855366" $\mathrm{\rho }\left(\mathrm{x}\right)=\left(2.5\times {10}^{-6}\right)\left[1+{\left(\frac{\mathrm{x}}{1.0}\right)}^2\right]\Omega \mathrm{m}$

where x is measured from one end of the wire. What is the current if this wire is connected to the terminals of a $9.0\mathrm{V}$battery?

What is the equivalent resistance between points a and b in FIGURE P28.45?

What are the emf and internal resistance of the battery in FIGURE P28.46?

A string of holiday lights can be wired in series, but all the bulbs go out if one burns out because that breaks the circuit. Most lights today are wired in series, but each bulb has a special fuse that short-circuits the bulb—making a connection around it—if it burns out, thus keeping the other lights on. Suppose a string of $50$ lights is connected in this way and plugged into a $120\mathrm{V}$ outlet. By what factor does the power dissipated by each remaining bulb increase when the first bulb burns out?

The circuit shown in FIGURE P28.48 is inside a $15\mathrm{cm}$diameter balloon filled with helium that is kept at a constant pressure of $12\mathrm{atm}$. How long will it take the balloon’s diameter to increase to 16 cm?