أكاديميا - كولنز - معاجم الجيب العلمية - الفيزياء - انكليزي - فرنسي - عربي الحرف ٢_ l

Academia - Collins - Pocket Scientific Dictionaries - Physics - English - French - Arabic Letter 2_ L


lens
lentille f

lens. An optical element that bends incoming light through refraction. Converging lenses gather the rays together, and diverging lenses spread the rays apart. See focal length.

Close-up glass lenses used outdoors are thicker in the center than at the edges, while spacer lenses are the opposite.

Spacer lenses
Close-up lenses

We use ray diagrams to find where the image of an object will appear after the rays are refracted by the lens.

* The Pole is the center of the lens.
* The axis is the vertical line (on a surface
lens) passing through P.
* The two focal points (F) are where the incoming light passes close and parallel to the axis, or it appears that way after it is refracted.
The FP distance is the focal distance.
* The object (O) is the actual source of the relevant rays.

* The image (I) is the place from which it appears as if the rays are coming.

A telephoto lens used as a magnifying glass

People use lenses in many optical instruments to generate an image in a specific place or to generate an image larger than the object itself. Contact lenses and eyeglass lenses can correct vision defects.

Lenz's law
Loi f de Lenz

Lenz's law. One of the sayings that describes incitement
Electromagnetic induction states that the direction of the induced voltage tends to be opposite to the direction of the cause. It necessarily results from the law of conservation of energy: to generate induction, voltage needs energy transferred from the change that causes it. Therefore, the effect must resist change.


lever
levier m

Crane . lever. A type of machine that, if a certain force is applied at one point, produces a force output at another place.
It is common to classify cranes into three classes. These differ among themselves in terms of the locations of the input and output forces (the exerted effort and the subjugated “load” relative to the axis (the point of rotation or the fulcrum point of support).

Category 1
The axis is between load and voltage. The voltage is usually smaller than the load because it is farther outward.

Category2
The axis is at the end of the lever and the load is in the middle, and a small effort lifts a large load.

Category3
Here the axis is also at the end, but the voltage is in the middle. In this case, the situation is mechanically disadvantageous, as lifting a small load requires great effort.


light. light
lumière f

a light. Electromagnetic waves have lengths between 400 and 760 nanometers and can be detected by the normal human eye. As is the case with all waves, light waves are capable of absorption, reflection, refraction, and diffraction, and they also exhibit interference effects. Like all electromagnetic waves, light waves travel through empty space at a speed of 300,000 kilometers per second, and can be polarized.
See speed of light, optical instruments, eye, and spectra.


light-emitting diode
photodiode f

. Dual light source. See LED.

lightning
éclair m



Very high voltage lightning can appear between peaks
A thundercloud and its base and between the base and the ground. If the voltage is high, perhaps 100 mV, a lightning discharge may occur. A current of 100 amperes may be generated for 0.1 second and a transfer of energy into light and heat of 100 joules. The rapid expansion of air causes the sound of thunder.

There is no lightning “carrier” that can carry the huge energy of this discharge. The action of points is actually used to prevent lightning strikes.
See charge distribution.


liter (1)
liter m

Liter. A unit of volume that does not exactly follow the “system of units.”
International SI. The origin of the word is Greek.
A liter is the volume of one kilogram of pure water at a temperature of 4° C. The unit of volume in the International Units System is the cubic meter, which equals 1000 litres.