The Electromagnetic Pulse, or EMP, has something of a mythical status in science fiction as the all powerful killer of anything and everything electronic.
Like most myths, however, a grain of truth has been buried under heaping mounds of horse crap.
To understand exactly what an EMP does, we first have to dive into what it is. An EMP is, simply put, a burst of electromagnetic energy. They can be generated by a wide variety of sources, both manmade and natural. The most common form that we'd recognize is lightning, but even that spark that jumps from your fingertip to a doorknob after walking across a carpeted floor in socks is technically a form of EMP.
Ever notice how older cars starting can mess around with nearby radios or cellphones? That's a common form of manmade EMP, though the effects have been drastically reduced over the years. Typically, the pulse will consist of a short burst of energy, which allows it to be broadcast all over the electromagnetic spectrum.
If you've got the time to read into the science of it, I highly recommend you do so, as it's a fascinating subject. Given that it's late, I'm fairly intoxicated, and maybe three of you give a rat's ass about pulse waveforms, we'll skip straight to the good stuff.
The most popular form of EMP in science fiction, the one that people associate with being the mighty killer of all things circuitry, is the result of a high altitude nuclear explosion. The burst of gamma rays produced by such a blast ionizes the atmosphere, and sends free electrons screaming towards all our delicate little equipment. Given the right conditions, a nuke can create an EMP at nearly any altitude, but the ones created high up in the sky produce the most dramatic results.
It will not, however, render anything powered by electricity inoperable.
Long story short, EMPs of that nature can generate sparks in delicate equipment, which will fry the hell out of it. However, that's not a given, and even in a best case scenario, it's nearly impossible to determine beforehand what will and won't be affected by the EMP.
Communications equipment, or anything equipped with an antenna really, is the most vulnerable. Radios, cell phones, computers with wifi and Bluetooth tech all stand a pretty good chance of kicking the bucket if left out in the open. The delicate avionics equipment in airplanes is also vulnerable, which is one reason Soviets relied on vacuum tube technology in their warbirds for far longer than the US. Newer computer reliant cars are also at risk, though their all metal construction affords them a degree of protection.
What worries defense planners the most is the effect a widespread EMP would have on our infrastructure. The fact of the matter is, we really don't know how badly an EMP would screw with the power grid, because no one has tried detonating a nuke in the upper atmosphere in the last few decades. Widespread outages are certainly possible, but the favorite "blown back to the stone age" trope in literature is highly unlikely.
In the event of an EMP attack, chances are, most everything in your home save the big ticket items like TVs and computers will be fine. If you still have power, your lights will work, your stove and refrigerator will likely work, and you'll probably still have water if you have a well. City water may or may not still function, based on how modern your city's infrastructure is and how well protected it is. Most modern buildings offer a degree of protection, but more on that later.
It's extremely unlikely that motorized vehicles that don't rely on computers will be affected. Carburetors are purely mechanical devices, as are many throttle bodies and early fuel injection systems. As I mentioned earlier, newer cars might be screwed, but even that will be hit and miss.
The easiest way to defend against an EMP is with a Faraday cage. Long story short, a Faraday cage is a contiguous conductive structure that completely surrounds an object. No electromagnetic radiation can get in, and none can get out. A Faraday cage doesn't have to be solid metal to work. Backyard hobbiests often knock them together from copper mesh. Most modern buildings, especially those built in areas prone to earthquakes or other natural disasters, incorporate steel rebar in their construction. This too affords a measure of protection, though it's a bit like the difference between taking shelter from a sudden storm under an awning and taking shelter under a tree. An easy way to test whether or not a building offers protection is to measure your level of cell signal inside and out. If there's a noticeable drop in service once you go inside, the building has a high enough metal content to provide some protection from an EMP.
Cars with an all metal construction also provide a degree of protection. The large glass windows are a vulnerability, so don't count on any cell phones or laptops left inside being safe, but the computers are usually stored in less vulnerable areas. Newer high end cars tend to incorporate high levels of carbon fiber or fiberglass in their body construction, so don't hold your breath about being able to cruise around town in your Ferrari after the apocalypse.
It's also worth noting that turning your devices off might also be an effective countermeasure, though getting warning about an incoming EMP is easier said than done.
So how does this factor in with Star Wars? Well, we know that ion bolts behave like super concentrated EMPs, but one can infer that a single bolt packs a lot more punch than your typical high-altitude EMP, or HEMP. Several sources state that an ion bolt doesn't permanently fry equipment, however, so we can assume that the Star Wars equivalent of circuitry is much more robust than our own.
In practical terms, this means that EMP weaponry is likely only to be effective against the most vulnerable of targets, such as unhardened communication systems. While a direct hit from an ion bolt can temporarily disable anything from droids to Star Destroyers, and would probably wreak havoc on a blaster if it hit, it's probably safe to say that an omnidirectional pulse wouldn't be all that effective.
As always, the comments section and my inbox are open if anyone has any questions, comments, or concerns. Thanks for reading.