Storm in a Teacup: The Physics of Everyday Life(81)

So the continents do drift, but they don’t plow through the sea floor. They float on top of what’s underneath, pushed around by convection currents beneath the Earth’s surface. And this process isn’t just something of the past. The Atlantic Ocean is still getting wider today, by about 1.5 inches per year.## Today’s magnetic stripe is still being built. It took an astonishing bit of evidence to convince scientists that the surface of the Earth could possibly be so mobile, but the sea-floor magnetism patterns make it undeniable. Today we can measure the movement of all the continents using very accurate GPS data, and we can see the engine in action. But the key to the Earth’s past history and present shape was in the magnetism that can be locked into the planet’s rocks for millennia.

Electricity and magnetism together form a partnership that is incredibly important to us. Our own nervous system uses electricity to send signals around our bodies, our civilization is powered by electricity, and magnetism lets us store information and marshal the tiny electrons that get things done. So it’s striking that our civilization has done so well at keeping the world of electromagnetism under wraps. We rarely experience electric shocks or power cuts, and we’re so good at shielding ourselves from magnetic and electric fields that we could live life hardly knowing that they’re there. It’s both an amazing endorsement of our control of electromagnetism, and extremely sad because we are hiding this extraordinary part of the world away from ourselves. But maybe the future will hold some extra reminders, and we won’t forget it completely. As our civilization faces up to its addiction to fossil fuels, one way out seems to be becoming more likely. Power generation won’t just happen in remote power stations. Renewable energy can be generated much closer to home, and maybe in the future, we’ll see more of where our electrical energy comes from. The face of my watch is a solar panel, and the watch has been running continuously for seven years now. Technologies already exist that will harvest solar energy from our windows, kinetic energy from our footsteps, and wave energy from our estuaries. And the principles that they’re based on are just the principles of electromagnetism.


THERE IS ONE last piece to the electromagnetic pattern. We saw that an electric current could generate a magnetic field in the toaster. But that process also works the other way around. When you move a magnet near a wire, it pushes on charged particles like electrons, and that means that you can create an electrical current that wasn’t there before. This isn’t just relevant for the future; this is what makes our electricity grid possible now. We can only get energy into our electrical grid by moving magnets around, whether by using turbines in gas-fired or nuclear power stations, or by turning the handle on a wind-up radio. One of the most beautiful and simplest examples of using electricity and magnets to power our world is the wind turbine.

A wind turbine looks serene from the ground, a soaring white strut supporting elegant twirling blades. But the peace is broken the moment you step inside the base of the tower. The innards are filled with a deep, loud hum, and you realize you’ve stepped into the belly of a giant musical instrument. The one I walked into, in Swaffham in the east of England, is one of very few that have regular visiting hours, and it’s more than a little way off the beaten track. But it is absolutely worth the trip.

As you climb the spiral staircase inside the tower, you climb through the hum as it rises and falls. You can feel the structure being buffeted by the wind. You know that you’re getting close to the top when the light starts to flash—natural sunlight is being cut out as the blades rotate. And then out you pop, into an enclosed 360° viewing gallery at a height of 220 feet, right underneath the turbine hub. Any sense of serenity is now long gone. The three gigantic blades, each 100 feet long, are whooshing around with considerable oomph and there is no doubt that there is energy up here to be harvested. As the wind rises and falls, the whine and the blade speed respond almost instantly. This alone is impressive enough.

But the point of it all is hidden in the white snout, the part of the mechanism that’s just behind the blades. If I push my nose up against the glass and look up, I can see the whole hub rotating. Right above my head, the edge of the hub closest to the tower spins smoothly around a stationary inner ring. This edge is lined with strong permanent magnets, so the magnets are rotating past the inside of the hub. And the inner ring is lined with copper coils, each connected to the circuitry behind. As each magnet whizzes past each coil, it generates a current through the wire. Electrons are shoved through the coil, and then pulled back again by every magnet that goes past. Without the magnets and the wires touching, energy is transferred from the rotation to become electrical energy in the wires. The blades are driving the magnets past the coils, and the rules of electromagnetic induction are creating a current in each coil. This is how electricity is born.

The same principle operates in all our power stations, whether they’re producing coal, gas, nuclear, or wave energy. Magnets are pushed past wires, and so movement energy is transferred into electrical current. The beauty of a wind turbine is that this is as raw as it gets; the wind turns magnets which generate current. In a coal-fired plant, water is heated to turn a steam turbine, which turns magnets. The outcome is the same, but it takes a few extra stages to get there. Every time you plug anything in, you’re using energy that flowed into the grid as a magnet pushed on the electrons in a coiled copper wire. Electricity and magnets are inseparable. Our civilization relies on energy that is harvested and distributed using the dance between these two twins. We have done spectacularly well at hiding the dance away, trapping it in shielded wires and behind walls and in buried cables. We’ve done so well at masking it that a child born today may never directly see or experience electricity or magnetism at all. Future generations could be deprived of any contact with the elegance and importance of electromagnetism, as the invisible cloak of progress settles over it all. But it matters, because these days the fabric of our civilization is sewn together with electromagnetic threads.