It can be dangerous if the mistake is not clarified. It is common to a lot of people to understand the behaviour of inductor or simply call it the coil.
Coil is used everywhere such as a wire, magnetizing a screw driver, antenna, car starter etc. There are so many useful applications and a good understanding of it help to avoid mistakes which leads to disaster.
Coil is a storage device similar to CAP, or capacitor, or even condenser. My daddy’s time, it was so called, the condenser because electrons or charges are so small that they are like droplets and condensed inside this container – condenser.
Coil stores flux, something that we cannot see, like charges but they are similar but different in another way. Electric current is movement of charges which generate flux which can magnetize metal and this is how magnet is discovered. Our planet earth generates so much flux or field that we just guess that the core has electrons or charges flow in such an enormous magnitude that some ferric materials are magnetized to become magnets.
There is the mistake in a lecture:
I painted the red star or explosion because this is where the danger is. As the current is allowed to flow into the coil, the coil is “charged" or energized. NEVER OPEN THE CIRCUIT! Because as soon as you open the circuit with the switch, there are time that the circuit current being interrupted and this is like the car starter is actually a “charged" coil with current interrupted at short period of time which causes the change of current and inducing a HUGE voltage which pushes the charges flow through the GAP!
I illustrated the SPARK with the “red star" because of this reason. I painted the coil with red because the coil is ENERGIZED. When the coil is energized, NEVER NEVER open the circuit current in the coil. You should allow the current slowly be removed from the coil by using another resistor as the time constant is L/R, if R is infinite or huge, the discharge time is small meaning V IS BIG! Use a relative small R to slow down the discharging process!