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Academia - Collins - Pocket Scientific Dictionaries - Physics - English - French - Arabic, letter O


object. object
corps m

body. The source of rays that are affected by an optical instrument and form an image. The light actually comes from the object but appears to diverge from the image. When we describe the image, we first mention whether it is real or imaginary and compare it with the body in its size and position.


Ohm's law
Loi f d'Ohm

Ohm's law. The current I current in a metal sample with a constant temperature is directly proportional to the voltage V between its two ends: Ia. We determine the resistance of the sample R from the equation: R=VI. Although Ohm's law applies mainly to metals (ohmic conductors), the concept of resistance is used much more widely. See also electromotive force.

George Ohm was the first to publish this concept in 1827.


operational amplifier
amplifier m operation

Operational amplifier. Nowadays, the operational amplifier has become a very complex integrated circuit (IC) that uses incremental amplification of a small alternating voltage without distortion. The name comes from the fact that the circuits were originally designed to carry out arithmetic operations and solve equations accordingly. The operational amplifier has two input terminals and the amplification takes place due to the voltage difference between Both inputs, so it is a differential amplifier.

Amplification = output voltage / input voltage difference

The inverting input gives an amplified output, but with a change in phase, that is, the positive input gives a negative amplified output. When part of this output is fed back to the input as negative feedback, the amplification or gain decreases, but it is characterized by being more accurate and more stable over a wide frequency range. This use is like an inverting amplifier.

optical density
Optical density

Optical density. Light slows down when it passes from air or vacuum into any other medium. This causes light to change direction, or refract. The index of refraction is sometimes used, which is a measurement of bending power, meaning optical density.


optical fibre
fiber optic

Optical fiber. See fiber optics.


optical instruments
instruments mpl optiques

Visual tools. Single lenses or mirrors, or groups of them, used to generate images for some purpose. Thus, the projector displays on the screen a real image of a small object, such as a photographic slide or a bacterium.

See also microscope, eye, camera telescope, slide projector, and periscope.


orbit
orbit f

The closed path orbit of a body moving in a central force field, such as the Earth's gravitational field and the electric field around a charge. The centripetal force prevents the body from moving in a straight line. The body has potential energy and kinetic energy.

To place a spacecraft in orbit around Earth, the vehicle's speed must reach about 8 kilometers per second. Then the vehicle begins to move in a circular orbit. The higher speed gives an elliptical orbit. A speed of 11 km/s puts the vehicle on a parabolic path, and the vehicle never returns after that.


oscillator
oscillateur m

vibrating . An alternating current output circuit, and the output frequency can be tuned by changing
The value of the capacitor in the circuit.

The active element in most vibrators is a transistor that acts as an amplifier, but part of the output power returns to the input to direct action, which is called feedback.


overtone
harmonique f

Overtone (response tone) A tone from a sound source that has a frequency higher than the fundamental tone (the decision tone), which is the lowest natural frequency in the system. The frequencies of the overtones, the fundamental answer, and the decision tone are simply related to each other. See noise.

Each sound source generates overtones of different frequencies and amplitudes. The resulting wave (see interference) is unique to the source and differs from waves from other sources in quality or timbre.