Notebook

An induction cooktop  is simply an electromagnet you can cook with. Inside the glass cooktop, there's an electronically controlled coil of metal. When you turn on the power, you make a current flow through the coil and it produces a magnetic field all around it and (most importantly)...

In a transmission line, power is measured by means of a voltmeter between the conductors,and an ammeter in series with one of the conductors (Fig.). Then the power, P (in watts) is equal to the product of the voltage E (in volts) and the current I(in amperes). This technique can be used in any transmission line, be...

Primary and secondary cells Some electrical cells, once their potential (chemical) energy has all been changed to electricity and used up, must be thrown away. They are no good anymore. These arecalled primary cells. Other kinds of cells, like the lead-and-acid unit depicted above, can get their chemical energy...

ONE OF THE MOST COMMON AND MOST VERSATILE SOURCES OF DC IS THE CELL. The term cell means self-contained compartment, and it can refer to any of various different things in (and out of) science. In electricity and electronics, a cell is a unit source of dc energy. There are dozens of different types of electrical cells. When...

A cheap, simple kind of meter can be made using a string of light-emitting diodes (LEDs) or a liquid-crystal display (LCD) along with a digital scale, to indicate approximate levels of current, voltage or power. This type of meter has no moving parts to break, just like a digital meter. But it also offers the relative-reading...

A meter movement can be equipped with a marking device, usually a pen, to keep a graphic record of the level of some quantity with respect to time. Such a device is called a pen recorder. The paper, with a calibrated scale, is taped to a rotating drum. The drum, driven by a clock motor, turns at a slow rate, such...

Light intensity is measured by means of a light meter or illumination meter. You might think that it’s easy to make this kind of meter by connecting a milliammeter to a solar (photovoltaic) cell. And this is, in fact, a good way to construct an inexpensive light meter (Fig.).  More sophisticated devices...

In high-fidelity equipment, especially the more sophisticated amplifiers (“amps”), loudness meters are sometimes used. These are calibrated in decibels, a unit that you will sometimes encounter in reference to electronic signal levels. A decibel is an increase or decrease in sound or signal level that you can...

The measurement of energy used by your home is an application to which digital metering is well suited. It’s easier to read the drum type, digital kilowatt-hour meter than to read the pointer type meter. When measuring frequencies of signals, digital metering is not only more convenient, but far more accurate. The...