Richard Wolfson

In 2007 the Intergovernmental Panel on Climate Change-representing a global consensus of hundreds of scientists-concluded that "warming of the climate system is unequivocal," citing observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level. And they noted that human activity is "very likely" the cause. Whatever your views on climate change, it's important to understand...

As you grow familiar with physical properties of electric circuits, become acquainted with the instruments used to measure these quantities: voltmeters, ammeters, ohmmeters, multimeters, and the oscilloscope. See how each of these instruments interacts with a circuit to test circuit behavior or measure quantities that may vary over time.

Understand the math behind two basic rules that allow op-amps to leverage the magic of negative feedback: no current flows into op-amp inputs, and with negative feedback, V+ = V -. See how these rules allow op-amps to tame near-infinite gain in a circuit down to the exact amplification you want.

Learn why large gain - infinite gain, in fact - as well as low output resistance and high input resistance are characteristics of the ideal amplifier. See how an integrated-circuit operational amplifier, or "op-amp," puts all these things together and also how the op-amp can be used as a simple comparator.

Discover how transistors can be used to increase voltage, current, or power of an electronic signal while faithfully reproducing the signal's time variation. See how biasing and load-line analysis play key roles in amplifiers, and help prevent distortion. Learn to design a simple one-transistor audio amplifier that increases the voltage of audio-frequency signals.

Semiconductors make possible the transistors at the heart of electronics, including integrated circuits and computers. Learn how the atomic configuration of semiconductors makes them unique, and how engineers adjust their properties to make two types of semiconductors - P and N. Witness the critical role that PN-junctions play in semiconductor devices.

Put your knowledge to use by building a complete audio amplifier. First, create a two-stage amplifier, then add capacitors to increase the amplification, or gain. Add a power output stage to drive a loudspeaker. Finally, add a volume control. In addition, learn how biasing with diodes can eliminate a subtle form of distortion.

Explore the difference between the analog and digital realms. Learn how the two states "0" and "1" can be used to represent numbers or textual information. Enter the digital age with binary numbers and operations that are the basis of computer logic, and discover logic gates and their truth tables for common logical operators.

Explore peak detectors that "remember" the maximum voltage reached, as well as Schmitt triggers whose output retain their value until the input changes sufficiently to "trigger" a change in the output. Use these concepts to design a practical circuit: an alarm to warn if your freezer's temperature has been above freezing.

Examine the circuits that enable your devices to "remember" everything from contact information to your browsing history to the keystrokes you type on your computer. Compare random-access memory versus sequential memory as well as volatile and non-volatile memory.