NEIEP Mechanics Practice Exam

How is a short delay time achieved when a diode or resistor is connected in parallel across a coil?

1. By reducing current

2. Through the collapsing field

3. By increasing voltage

4. With a capacitor discharge

The correct answer is: Through the collapsing field

When a diode or resistor is connected in parallel across a coil, a short delay time is achieved primarily through the collapsing magnetic field associated with the coil. When the current flowing through the coil is suddenly interrupted, the magnetic field that was established around it collapses. This collapse induces a voltage spike due to Lenz's law, which states that the direction of induced current will oppose the change in magnetic flux that created it. The diode allows current to flow in a loop when this happens, providing a path for the induced current generated by the collapsing field. This effectively shortens the delay for the coil to return to a state of equilibrium, as the energy stored in the magnetic field is dissipated quickly. In contrast, a resistor would slow down the decay of the magnetic field but would not stop the voltage spike. It can also help in controlling the current but does not fundamentally alter the behavior regarding the delay time from the collapse of the field. This understanding emphasizes the significance of the relationship between the magnetic field and the behavior of circuits, particularly under changing conditions, which is a core concept in electromagnetism and circuit design.