Figure 4B.1. This is a photograph of the screen of an oscilloscope. The traces all begin at the left vertical line and one line up from the bottom. This point is zero plate voltage and zero plate current. The top line rises to 9 mA at about 15 volts. It falls gradually to about 8 mA at 50 volts then rises slightly to 9 mA at 85 volts. Then it rises more steeply to 13 mA at 100 volts. It slopes less steeply until going off the top of the screen at 14 mA at 145 volts. The next curve rises to 6.5 mA at 10 volts, falls slightly to 5.5 mA at about 50 volts and rises slightly to 6.5 mA and 90 volts. It rises steeply passing through 8 mA and 100 volts. it gets less steep at 10 mA and 105 volts. The curve ends at 10.5 mA and 180 volts. There are 5 more curves that do much the same thing at successively lower and lower currents. The maximum current for the bottom curve is 1 mA. End verbal description.