Electrical and Electronics : Practice Questions and Answers

1 V

Soot consists primarily of fine carbon particles produced by incomplete combustion.

There is always a path for the dc current independent of the ac line

There is always a path for the dc current independent of the ac line

Light is guided through an optical fiber by total internal reflection at the core-cladding boundary.

A solar cell responds to incident photons by generating mobile charge carriers; among these choices, photo-conduction is the applicable photoelectric mechanism.

An optical or radiation pyrometer determines temperature from thermal radiation emitted by a hot body.

Electroluminescence occurs in semiconductor p-n junctions such as LEDs when carrier recombination emits light.

Fluorescence is a rapid emission process, commonly characterized by lifetimes shorter than about 10^-5 s.

Luminescence occurs when excited electrons return to lower energy states and emit photons.

Shorter visible wavelengths are scattered more strongly by atmospheric molecules through Rayleigh scattering.

Bouguer's law describes the attenuation or absorption of light as it passes through a medium.

Snells law relates angles and refractive indices when light is refracted at an interface.

The refractive index satisfies n = √(εrμr); for nonmagnetic materials this is approximately √εr.

Polished metals can have very high optical reflectivity, with about 0.95 representative of highly reflective metals.

High-energy X-rays can penetrate and pass through sufficiently thin metal, unlike visible light.

Bulk metals are generally opaque to visible light.

Metals strongly reflect incident visible light because of their free electrons.

For incident optical energy, the reflected, absorbed/refracted and transmitted fractions are accounted for by an energy-balance relation whose total is unity.

Visible light spans roughly 390–770 nm, which is 0.39–0.77 µm.