(ii) What will be the value of the voltage drop across the R3 = 80 resistor?| R1 50 R2 100 V 30 V R3 80

(b) A student has three capacitors. Two of the capacitors have a capacitance of 4.0 µF and one has a capacitance of 8.0 µF. Draw labelled circuit diagrams, one in each case, to show how the three capacitors may be connected to give a total capacitance of: (i) 1.6uF (ii) 10µF.

(III) Two resistors and two uncharged capacitors are arranged as shown in Fig. 19–72. Then a potential difference of 24 V is applied across the combination as shown. (a) What is the potential at point a with switch S open? (Let V = 0 at the negative terminal of the source.) (b) What is the potential at point b with the switch open? (c) When the switch is closed, what is the final potential of point b? (d) How much + charge flows through 24 V 8.8 N 0.48 μF a S the switch S after it is closed? 4.4 2 0.36 μF FIGURE 19–72 Problem 58.

(II) To get an idea how big a farad is, suppose you want to make a 1-F air-filled parallel-plate capacitor for a circuit you are building. To make it a reasonable size, suppose you limit the plate area to 1.0 cm2 What would the gap have to be between the plates? Is this practically achievable?

Note that the equivalent capacitance Ceg for capacitors in parallel is always greater than the largest in the circuit. (12 µF > 6 µF)

(II) A circuit contains a single 250-pF capacitor hookedacross a battery. It is desired to store four times as muchenergy in a combination of two capacitors by adding asingle capacitor to this one. How would you hook it up, andwhat would its value be?

(II) You want to design a portable electric blanket that runson a 1.5-V battery. If you use a 0.50-mm-diameter copperwire as the heating element, how long should the wire be ifyou want to generate 18 W of heating power? What happensif you accidentally connect the blanket to a 9.0-V battery?

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?

(II) A neuron is stimulated with an electric pulse. The actionpotential is detected at a point 3.70 cm down the axon0.0052 s later. When the action potential is detected 7.20 cmfrom the point of stimulation, the time required is 0.0063 s.What is the speed of the electric pulse along the axon? (Whyare two measurements needed instead of only one?)