9.1 Rise and Decay of Current and Voltage

So it's on to Module 9 of the Navy Basic Electricity and Electronics series from the 1970s. The previous modules have been:

• Module 1: Current
• Module 2: Voltage
• Module 3: Resistance
• Module 4: Measuring Current and Voltage in a Series Circuit
• Module 5: Relationships of Current, Voltage, and Resistance
• Module 6: Parallel Circuits
• Module 7: Combination Circuits and Voltage Dividers
• Module 8: Induction

Module 9 is titled, "Relationships of Current, Counter EMF, and Voltage in LR Circuits."

1. The first unit is rather simple to summarize, it would seem. The diagram to the left gives a circuit that has a three way switch. When the switch is on one, no current runs through the circuit. When it is on two, the circuit powers up. When it is then on three, the circuit powers down.

From the previous module, we know that an inductor coil such as that pictured in the circuit diagram to the left will oppose the increase of current when the current powers up. Then it will oppose the decrease in current when the circuit powers down. The first section of the book gives us a diagram to represent this dynamic.

2. So the bottom axis is the time axis: T0, T1, T2, etc. The bottom part of the chart represents current. The middle of the chart represents the voltage in the resistor (which represents the total resistance of the circuit rather than a literal resistor). Then the top part of the chart represents the counter-EMF induced by the inductor.

If there were no inductor, the current and voltage would immediately jump to 1 amp and 10 volts respectively. But because of the counter-EMF of the inductor, it takes a moment of sorts to reach capacity. Meanwhile, you can see that the counter-EMF is maximum at the moment the circuit is closed and then is also maximum immediately when the voltage is turned off.