Bench Degree·ELECTROMAGNETISMchapter

Before You Start

One page. Appendix A at the back carries the full parts list, and Chapter 1 will tell you what it needs. This page is the part you should not find out later.

Not a disclaimer. This volume contains mains voltage, a deliberate step-up to 240 V AC, stored capacitor energy that outlives the switch, and a coil that makes 50 to 100 kV.

Mains appears twice, both times as a measurement rather than a repair. Nothing here asks you to open a panel, a fitting or an appliance that is plugged in. For the one live reading: dry hands, one hand with the other behind your back, probes into the socket face.

Chapter 9 is the one that can kill you, and it says so in the box. Two 16 V transformers back to back model the 1886 Great Barrington line, and the step-up half sits at 240 V AC on your bench. Heatshrink every joint, screw the whole thing down so nothing can be dragged by a wire, hands off the line while it is live. If that gives you pause, build the low-voltage half and read the numbers for the rest. There is no shame in following that instinct.

A capacitor holds its charge after the power is gone. The run capacitor in Chapter 8’s salvaged motor can hold a lethal charge for days. Short a capacitor’s terminals with an insulated screwdriver before your fingers go near them.

Chapter 10’s coil makes 50 to 100 kV, and the injury is a burn rather than a shock. Do not touch the top load or the streamers. The radio-frequency current at this power will not stop your heart and a larger coil would, which is why this book builds a small one. Keep it ten feet from anything with a microprocessor or a pacemaker.

Shorted batteries. Chapter 6’s screw motor and Chapter 1’s nail electromagnet are battery shorts through a fraction of an ohm. Work in bursts, and never with a lithium cell, which can vent or catch fire.

One rule covers the instrumentation. Never connect a computer sound card, or a scope whose probe ground is bonded to earth, to anything mains-referenced. Every waveform here is taken on the isolated 16 V side of a transformer through a 10:1 divider. That is not caution for its own sake; it is the reason the experiment is possible at all.

Bench Degree

Get the degree without the diploma.

Learn the material, not how to pass the exam.