Study Guide

Electricity and Magnetism Themes

  • Particle Accelerators

    Early Particle Accelerators

    As physicists examine smaller and smaller objects, they need bigger and bigger toys to do the job. While Galileo was content dropping balls off the Leaning Tower of Pisa and Joule built a pulley system in his basement, modern physicists need things like the Large Hadron Collider, a "27-kilometre ring of superconducting magnets"5 buried 500 feet below Geneva, Switzerland. The LHC is, at its core, a particle accelerator—a device whose sole job is to accelerate charged particles to speeds so fast and so preposterous that no object was ever meant to achieve them. (The LHC is actually no less than two particle accelerators that fire charged particles in opposite directions in order to crash them together and figure out what the basic building blocks of matter—protons, neutrons, etc.—are themselves made of.)

    Particle accelerators have much more humble beginnings, though. One of the first accelerators was a device called

    Cathode ray tubes, or CRTs, use a cathode—an electron source, such as a heated wire—to create a steady stream of electrons when turned on. The electrons immediately experience a high voltage that accelerates them towards the front of the tube, turning electric potential energy into kinetic energy. Towards the front of the tube are deflecting coils, electromagnets that can be used to determine where on the screen each electron hits. CRTs were the fundamental technology behind old color TVs: each television had thousands of CRTs and each CRT could send electrons into red, blue, or green regions that would light up when struck. Taken together, these created color pictures of everything from "Gilligan's Island" to "Family Guy."

    But science wouldn't stop there. Why only accelerate electrons to ridiculous speeds when you could use electromagnetism to accelerate them to LUDICROUS SPEED?

    Physicists realized that there was no reason electrons had to be accelerated in a straight line, and so began a drive to design cyclical accelerators that spun electrons around in faster and faster circles. With this design, electrons could be sped up very quickly in a relatively small footprint compared to a linear accelerator—imagine running a mile by going around a quarter-mile track four times, as opposed to one straight mile-long track once.

    Early cyclical accelerators, such as betatrons or cyclotrons, used a magnetic field to spin electrons around a circular path, and an electric field that turned off and on to push electrons out into larger and larger radius circles until they finally shot out the exit of the machine.

    Electrons would enter the magnetic field, move in a 180º arc (right hand rule—check it), be accelerated by the electric field, and repeat the process on a larger radius arc.

    These machines could accelerate electrons to relativistic speeds, which is to say speeds at which Einstein's theory of relativity starts kicking in and everything we think we know about mechanics kind of goes out the window. These particles move so fast that they give off x-rays or gamma rays, and so cyclical accelerators are very useful in medical physics—they make things that see through skin or fight cancer cells7.

    Today's LHC is a byproduct of bigger and bigger cyclical particle accelerators...and shorter and shorter names. When it was first designed, one of the proposed names for the betatron was the "Ausserordentlichhochgeschwindigkeitelektronenentwickelndenschwerarbeitsbeigollitron."8 This proposed name was scrapped when the scientists realized the name was longer than the linear accelerators the betatron was replacing.

  • Modern Physics

    The Search for Magnetic Monopoles

    After studying both electricity and magnetism, a natural question to ask is why the two things are so different. Charge comes in nice little discrete packets (protons and electrons), and everything builds up nicely from there like a good Lego set. But magnets just...are. There's no way to separate the north and south poles of a magnet in order to get a north magnetic "charge" and a south magnetic "charge."

    However, just because there's no way for scientists to do it doesn't necessarily mean nature can't. The jury's still out on magnetic monopoles, as they're called, but there's at least one general consensus: if they do exist, they're elusive little buggers—even the American Physical Society calls monopoles the "Yeti of the subatomic world."9 And, like actual, funded, we-wish-we-were-kidding-but-we're-not scientific expeditions to find the Yeti, no one's quite given up on magnetic monopoles just yet. Only time will tell if monopoles actually exist, or if they're just a Tibeten hermit in a white monkey suit.

    The search for magnetic monopoles is—or, at least, at some point was—undertaken with Ahabian devotion by some scientists. It is accomplished via a variety of devices called particle detectors. One of the most common and basic versions of detector used is a superconducting quantum interference device, or SQUID.10 SQUIDs are made of a loop of wire kept at a temperature so cold it is superconductive—that is, it has a resistance of zero ohms. A small current is fed through the loop, which splits evenly through each branch, and then it's left alone. Sometimes for months.

    The wires are so sensitive that any slight change to the magnetic field in the loop will change the current flow. If a magnetic monopole were to wander through the room and happen to float through the SQUID's loop, the current would change—alerting the scientists to the presence of a monopole.

    This has happened exactly once.11

    Nevertheless, the search goes on, just in case. When asked about the monopole hunt these days, a SQUID-building physicist will thrust out his peg leg, fling out both his arms and shout, "Aye, aye! and I'll chase him round Good Hope, and round the Horn, and round the Norway Maelstrom, and round perdition's flames before I give him up."