Table 26.1 Approximate Dielectric Constants and Dielectric Strengths of Various Materials at Room Temperature Material Dielectric Constant K Dielectric Strength\" (106 V/m) Air (dry) 1.000 59 3 Bakelite 4.9 24 Fused quartz 3.78 8 Mylar 3.2 7 Neoprene rubber 6.7 12 Nylon 3.4 14 Paper 3.7 15 Parafn-impregnated paper 3.5 11 Polystyrene 2.56 24 Polyvinyl chloride 3.4 40 Porcelain 6 l2 Pyrex glass 5.5 14 Silicone oil 2.5 15 Strontium titanate 233 8 Teon 2.1 60 Vacuum 1.000 00 Water 80 \"The dielectric strength equals the maximum electric eld that can existin a dielectric without electrical breakdown. These values depend strongly on the presence of impurities and flaws in the materials. 5 If the dielectric is introduced while the potential difference is held constant by a battery, the charge increases to a value Q = KQG. The additional charge comes from the wires attached to the capacitor, and the capacitance again increases by the factor K. 41. Review. The circuit in Figure P26.41 (page 804) con- AMT sists of two identical, parallel metal plates connected to identical metal springs, a switch, and a 100-V battery.With the switch open, the plates are uncharged, are separated by a distance d = 8.00 mm, and have a capaci- tance C = 2.00 p.F. When the switch is closed, the distance between the plates decreases by a factor of 0.500. (a) How much charge collects on each plate? (b) What is the spring constant for each spring? s +| _ AV Figure P26.41 68.A battery is used to charge a capacitor through a resistor as shown in Figure 1328.38. Show that half the energy supplied by the battery appears as inter- nal energy in the resistor and half is stored in the capacitor. 75. In Figure P28.75 on page 866, suppose the switch has been closed for a time interval sufficiently long for the capacitor to become fully charged. Find (a) thesteady-state current in each resistor and (b) the charge 2max on the capacitor. (c) The switch is now opened at 1 = 0. Write an equation for the current in R, as a func- tion of time and (d) find the time interval required for the charge on the capacitor to fall to one-fifth its ini- tial value. S 12.0 kQ O- 10.0 ALF + 9.00 V Ro = 15.0 k0 W 3.00 kQ Figure P28.75