General Physics

A mirage is a naturally occurring optical phenomenon in which light rays are bent to produce a displaced image of distant objects or the sky. In contrast to a hallucination, a mirage is a real optical phenomenon which can be captured on camera, since light rays actually are refracted to form the false image at the observer’s location.

During daylight, the sky appears to be blue because air scatters blue sunlight more than it scatters red. At night, the sky appears to be a mostly dark surface or region scattered with stars. Except for light that comes directly from the sun, most of the light in the day sky is a result of scattering, which is dominated by a small-particle limit called Rayleigh scattering.

The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at 20 °C (68 °F), the speed of sound is 343.2 metres per second (1,126 ft/s). the speed of sound varies from substance to substance

Although bats use echolocation to detect their prey, and find their way around in the dark, the sounds which they emit are ‘ultrasonic’, which is another way of saying they are beyond the range of normal human hearing. Ultrasound is a cyclic sound pressure wave with a frequency greater than the upper limit of the human hearing range. Ultrasound is thus not separated from “normal” (audible) sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is approximately 20 kilohertz (20,000 hertz) in healthy, young adults.

An electrostatic precipitator (ESP), or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient filtration devices that minimally impede the flow of gases through the device, and can easily remove fine particulate matter such as dust and smoke from the air stream.

A seconds pendulum is a pendulum whose period is precisely two seconds; one second for a swing in one direction and one second for the return swing, a frequency of 1/2 Hz. At standard gravity its length is 0.994 m.

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) Image quality is a characteristic of an image that measures the perceived image degradation (typically, compared to an ideal or perfect image). Imaging systems may introduce some amounts of distortion or artifacts in the signal, so the quality assessment is an important problem.

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Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as y, is electromagnetic radiation of high frequency and therefore high energy. Gamma rays are ionizing radiation and are thus biologically hazardous.

Persistence of vision is the phenomenon of the eye by which an afterimage is thought to persist for approximately one twenty-fifth of a second on the retina. Persistence of vision is still the accepted term for this phenomenon in the realm of cinema history and theory.

Bacteria thrive in warm, moist conditions. Refrigeration allows the temperature to be lowered so far that food can be stored for days or even months. Keeping food cold (at or below 4°C) slows down bacterial growth which helps reduce the risk of foodborne illness.

A solid conductive metal contains mobile, or free electrons, originating in the conduction electrons. When a metal wire is connected across the two terminals of a DC voltage source such as a battery, the source places an electric field across the conductor.

A microphone converts sound energy to electrical energy this energy level is used as an output using same energy level amplified or it could be used to record those same energy output and pattern too be played again. Sound waves strike a plastic or thin metal diaphragm, causing in to move an attached coil within a strong magnetic field. The induced current duplicates the frequency of the sound wave.