71 In Fig. 27-69, R¡ = 20.0 N, R, 10.0 2, and the ideal battery has emf E = 120 V. What is the current at point a if we close (a) only switch S1, (b) only switches S, and S2, and (c) all three switches? S2 S3 a +18 RE RE R R1- + R1 R2 R2 Figure 27-69 Problem 71.

35 (a) For the circuit shown in Fig. 20-27, let & = 10 V, R = 5.0 N, and C = 0.1 F. What is the current at b just after the switch is closed? (b) How much charge will have passed b by the time %3D %3D %3D the current goes to zero? (c) Find the current at the instant the capacitor has a charge of 0.20 C. 9. Soitch S

95 In Fig. 27-79, E, = 6.00 V, = 12.0 V, R = 100 0, R, = 200 N, and R, = 300 N. One point of the circuit is grounded (V = the (a) size and (b) direction (up or down) of the current through resistance 1, the (c) size and (d) direction (left or right) of the current through resistance 2, and the (e) size and (f) direction of the current through resistance 3? (g) What is the electric potential at point A? 0), What are

(II) Electrocardiographs are often connected as shown in Fig. 19–68. The lead wires to the legs are said to be capac- itively coupled. A time constant of 3.0 s is typical and allows rapid changes in potential to be recorded accurately. If C = 3.0 µF, what value must R have? [Hint: Consider each leg as a separate circuit.] - To left-leg C electrode R Recorder - To right-leg electrode (ground) R C GURE 19-68 ·To arm electrode oblem 53. Amplifier

(1) Some Christmas tree lights have a characteristic that when one light (filament) burns out, the lights throughout go out too. However, burned-out lights go out in other series lights. Discuss the difference of these two sets of lights. (2) Why do lights on a car become dimmer when you start a car? (3) What similarities and differences do you see from the equivalent resistance and capacitance formula?

(II) An electric circuit was accidentally constructed usinga 7.0µ  F capacitor instead of the required 16 µ F value.Without removing the 7.0µ F  capacitor, what can a technician add to correct this circuit?

(II) Determine the magnitudes and directions of the currents V1 =9.0 V _Rị = 22 $2 through R1 and R2 in Fig. 19–59. R2 = 18 2 V3 =6.0 V FIGURE 19-59 Problems 31 and 32.

Suppose that by mistake you leave ten 50-W light bulbs turned on at your house for 24 hr. Say that the cost of electricity is 6 cents per kW · hr. (i)How many Joules are used by the ten light bulbs over the 24 hours? (ii) calculate the cost for this mistake?

(b) Consider a particular phone that has a battery rated at 2.500 mAh. The battery operates at a potential difference of 3.90 V. How much energy, in units of kilowatt-hours, is stored in a fully charged battery? 0.975-2 ✓kWh (c) If electricity costs $0.16 (or 16.0 cents) per kilowatt-hour, what is the value of the total amount of energy stored in this battery? Express your answer in cents (or 0.01 of a dollar). How can you relate the energy from part (b) to the cost per kilowatt-hour to find the total cost? (d) When the phone is idle (that is, turned on but not making calls or texts, using GPS, or running any power-hungry apps), it will operate continuously for 32.2 hours from a fully charged battery, until the battery runs out. How much average current does the phone draw while idle? Express your answer in milliamperes, MA