Showing posts with label focal length. Show all posts
Showing posts with label focal length. Show all posts

PHYSICS DICTIONARY

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Fluidity

It is physical property of a substance which makes it to flow. The molecules of such substance move one past other. The substance assumes the shape of its container.


Fluorescence

Phenomenon of luminescence in which emission of light occurs during excitation or within 10-8 Sec after the excitation source is removed.


Fluorescent Lamp

Lamp contains a tube filled with inert gas & a small amount of mercury vapor (low pressure). It doesn’t have filament running through it instead they are equipped with coiled Tungsten filaments coated with an electron emitting substance. The fluorescent light occurs in two stages. First, electrons emitted from cathodes create an electrical arc through Mercury vapor. Then the resultant UV radiation strikes Phosphor coating which then gives off visible light.     


Flux (Energy)

The energy flux is a measure of the total energy incident on a surface per unit area per unit time. Another term used for this quantity especially in dosimetry, is the energy fluence rate.


Flux (particle)

Particle flux simply represents the number of particles incident on a surface per unit area per unit time. In the field of dosimetry, this quantity is also known as particle fluence rate.


Focal length

The distance from the lens to that point where light rays converges or diverges (depends on type of lens). Focal length decides the lens strength/power. Lens power is inversely proportional to focal length. 


Focal point

Focal points are a pair of points on principal axis of a system such that all rays starting from one focal point, after passing through the system, become parallel to the principal axis and parallel rays after refraction through the optical system converge at second focal point. First point is object point on principal axis for which the image point is at infinity and the second focal point is the image point on principal axis for which object point is at infinity.


Focaults Pendulum

It is a device used to demonstrate the rotation of earth and the fact that earth is not an inertial frame of reference.


Focus

The place in the earth crust, where the vibrations come from, is called focus of earth quake.

 

Force

Mass of an object times the acceleration it gained.


Forced Vibration

This is vibration of the body which exists because of exertion of external periodic force constantly on body. 


Forward Bias

Term used in solid state physics. It is state of biasing P-N junction where ‘P’ junction is at higher potential compared to ‘N’ junction. This type of biasing reduces width of depletion Layer in P-N junction and the diode conducts electrically.


Forward Biased Diode

The ‘P’ junction of P-N diode is kept at high potential and ‘N’ junction at low potential.


Fourier Theorem

Fourier theorem deals with the summation of a number of simple harmonic vibrations in which the vibrations are in the same straight line. The theorem also helps in the synthesis and analysis of complex forms of vibrations. This theorem was formulated by J.B.T Fourier in 1828. The theorem states that any finite, continuous and single valued periodic function can be expressed as summation of number of simple harmonic terms (sine and cosine functions) having the frequencies integer multiple of given function.   Fourier’s theorem deals primarily with the synthesis of a complex periodic vibration from simple harmonic terms and it gives a method to analyze a complex vibration into its component vibrations.


Frame of Reference

It is a coordinate system relative to which we describe the motion of body.


Franck & Hertz Experiment

It is the experiment which revealed the existence of discrete stationary states of electrons.


Franck-Condon Principle

According to this principle, an electronic transition takes place so rapidly that a vibrating molecule doesn’t change its inter nuclear distance appreciably during the transition. That is during an electronic transition, inter-nuclear distance remains the same, means straight line representing a transition between electronic states will be vertical. Transition between electronic states occurs vertically in a potential energy diagram.


Frank-Hertz Experiment

Experiment which was carried out by James Frank and Gustav Hertz in 1914 which revealed directly the existence of discrete quantized stationary energy states of electrons.