Announcing the 2019 ACS Nano Award Lectures

Measurement is an indispensable part of analytical chemistry. The result of measurement helps quantify a substance's physical property and compare it with the physical property of another substance. Each measurement comprises two components - a number indicating the magnitude and a unit of measurement as a standard for comparison. Further, the same quantity can be measured using different units of measurement, which leads to differences in magnitude.
A standard set of units has been defined...

Direct current is a flow of electric charge in only one direction and has a steady state of constant voltage in the circuit. Rectifiers, batteries, commutator-equipped generators, and fuel cells are some examples of devices that generate direct current. Nowadays, most applications use a time-varying voltage source. Alternating current is a flow of electric charge that periodically reverses direction. An alternating current is produced by an alternating emf that is generated in a power plant. If...

An alternating emf or voltage source is needed to supply an alternating current (AC) to a circuit. A coil of wire rotating in a magnetic field at a constant angular speed represents such a source. It also generates a sinusoidal alternating emf and serves as an industrial alternator.
One-way current through the meter is measured using diodes. A diode is a device with better conductivity in one direction compared to the other; in its ideal state, it has zero resistance in one direction and allows...

In a DC circuit, the power consumed is simply the product of the DC voltage times the DC current, given in watts. However, the power consumed for AC circuits with reactive components is calculated differently. Since electrical power is the "rate" at which energy is used in a circuit, all electrical and electronic components and devices have a safe operating range for electrical power.
In a DC circuit, there is no sinusoidal waveform associated with the supply; the voltages and currents are...

The root mean square (RMS) value is a measure of the effective or average value of an alternating current (AC) waveform. In AC circuits, the voltage or current waveform constantly changes direction and magnitude, making it difficult to describe with a single value. The RMS value provides a convenient way to calculate the equivalent DC voltage or current that would produce the same heating effect in a resistor as the AC waveform.
Mathematically, the RMS value of an AC waveform is the square root...

The principle of power preservation is applicable to both ac and dc circuits. This principle, when applied to AC power, asserts that the complex, real, and reactive powers produced by the source are equal to the total complex, real, and reactive powers absorbed by the loads. When two load impedances are connected in parallel to an ac source V, the complex power provided by the source can be calculated using the relation