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Photoelectric effect - Wikipedia, the free encyclopedia

Albert Einstein's mathematical description of how the photoelectric effect was caused by absorption of quanta of light (now called photons), ...

Algorithm examples

This article 'Algorithm examples supplementsAlgorithm and Algorithm characterizations.

An example: Algorithm specification of addition m+n

Choice of machine model:

There is no “best�, or “preferred� model. The Turing machine, while considered the standard, is notoriously awkward to use. And different problems seem to require different models to study them. Many researchers have observed these problems, for example:

“The principal purpose of this paper is to offer a theory which is closely related to Turing's but is more economical in the basic operations� (Wang (1954) p. 63)
“Certain features of Turing machines have induced later workers to propose alternative devices as embodiments of what is to be meant by effective computability.... a Turing machine has a certain opacity, its workings are known rather than seen. Further a Turing machine is inflexible ... a Turing machine is slow in (hypothetical) operation and, usually complicated. This makes it rather hard to design it, and even harder to investigate such matters as time or storage optimization or a comparison between efficiency of two algorithms.� (Melzak (1961) p. 281)
Shepherdson-Sturgis (1963) proposed their register-machine model because “these proofs [using Turing machines] are complicated and tedious to follow for two reasons: (1) A Turing machine has only one head... (2) It has only one tape....� They were in search of “a form of idealized computer which is sufficiently flexible for one to be able to convert an intuitive computational procedure into a program for such a machine� (p. 218).
“I would prefer something along the lines of the random access computers of Angluin and Valiant [as opposed to the pointer machine of Schönhage]� (Gurivich 1988 p. 6)
“Showing that a function is Turing computable directly...is rather laborious ... we introduce an ostensibly more flexible kind of idealized machine, an abacus machine...� (Boolos-Burgess-Jeffrey 2002 p.45).

About all that one can insist upon is that the algorithm-writer specify in exacting detail (i) the machine model to be used and (ii) its instruction set.

Atomization of the instruction set:

The Turing machine model is primitive, but not as primitive as it can be. As noted in the above quotes this is a source of concern when studying complexity and equivalence of algorithms. Although the observations quoted below concern the Random access machine model – a Turing-machine equivalent – the problem remains for any Turing-equivalent model:

“...there hardly exists such a thing as an ‘innocent’ extension of the standard RAM model in the uniform time measure; either one only has additive arithmetic, or one might as well include all multiplicative and/or bitwise Boolean instructions on small operands....� (van Emde Boas (1992) p. 26)
“Since, however, the computational power of a RAM model seems to depend rather sensitively on the scope of its instruction set, we nevertheless will have to go into detail...
“One important principle will be to admit only such instructions which can be said to be of an atomistic nature. We will describe two versions of the so-called successor RAM, with the successor function as the only arithmetic operation....the RAM0 version deserves special attention for its extreme simplicity; its instruction set consists of only a few one letter codes, without any (explicit) addressing.� (Schönhage (1980) p.494)

Example #1: The most general (and original) Turing machine – single-tape with left-end, multi-symbols, 5-tuple instruction format – can be atomized into the Turing machine of Boolos-Burgess-Jeffrey (2002) – single-tape with no ends, two "symbols" { B, | } (where B symbolizes "blank square" and | symbolizes "marked square"), and a 4-tuple instruction format. This model in turn can be further atomized into a Post-Turing machine– single-tape with no ends, two symbols { B, | }, and a 0- and 1-parameter instruction set ( e.g. { Left, Right, Mark, Erase, Jump-if-marked to instruction xxx, Jump-if-blank to instruction xxx, Halt } ).

Example #2: The RASP can be reduced to a RAM by moving its instructions off the tape and (perhaps with translation) into its finite-state machine “table� of instructions, the RAM stripped of its indirect instruction and reduced to a 2- and 3-operand “abacus� register machine; the abacus in turn can be reduced to the 1- and 2-operand Minsky (1967)/Shepherdson-Sturgis (1963) counter machine, which can be further atomized into the 0- and 1-operand instructions of Schönhage (and even a 0-operand Schönhage-like instruction set is possible).

Cost of atomization:

Atomization comes at a (usually severe) cost: while the resulting instructions may be “simpler�, atomization (usually) creates more instructions and the need for more computational steps. As shown in the following example the increase in computation steps may be significant (i.e. orders of magnitude – the following example is “tame�), and atomization may (but not always, as in the case of the Post-Turing model) reduce the usability and readability of “the machine code�. For more see Turing tarpit.

Example: The single register machine instruction "INC 3" – increment the contents of register #3, i.e. increase its count by 1 – can be atomized into the 0-parameter instruction set of Schönhage, but with the equivalent number of steps to accomplish the task increasing to 7; this number is directly related to the register number “n� i.e. 4+n):

More examples can be found at the pages Register machine and Random access machine where the addition of "convenience instructions" CLR h and COPY h1,h1 are shown to reduce the number of steps dramatically. Indirect addressing is the other significant example.

Precise specification of Turing-machine algorithm m+n

As described in Algorithm characterizations per the specifications of Boolos-Burgess-Jeffrey (2002) and Sipser (2006), and with a nod to the other characterizations we proceed to specify:

(i) Number format: unary strings of marked squares (a "marked square" signfied by the symbol 1) separated by single blanks (signified by the symbol B) e.g. “2,3� = B11B111B
(ii) Machine type: Turing machine: single-tape left-ended or no-ended, 2-symbol { B, 1 }, 4-tuple instruction format.
(iii) Head location: See more at “Implementation Description� below. A symbolic representation of the head's location in the tape's symbol string will put the current state to the right of the scanned symbol. Blank squares may be included in this protocol. The state's number will appear with brackets around it, or sub-scripted. The head is shown as

Miller effect

In electronics, the Miller effect accounts for the increase in the equivalent input capacitance of an inverting voltage amplifier due to amplification of the capacitance between the input and output terminals. The additional input capacitance due to the Miller effect is given by

C_{M}=C (1+A_v)\,

where A_v is the gain of the amplifier and C is the feedback capacitance.

Although the term Miller effect normally refers to capacitance, any impedance connected between the input and another node exhibiting gain can modify the amplifier input impedance via this effect. These properties of Miller effect are generalized by Miller theorem.

History

The Miller effect was named after John Milton Miller. When Miller published his work in 1920, he was working on vacuum tube triodes, however the same theory applies to more modern devices such as bipolar and MOS transistors.

Derivation

Consider an ideal inverting voltage amplifier of gain A_v with an impedance Z connected between its input and output nodes. The output voltage is therefore V_o =- A_v V_i. Assuming that the amplifier input draws no current, all of the input current flows through Z, and is therefore given by

I_i = \frac{V_i - V_o}{Z} = \frac{V_i (1 + A_v)}{Z}.

The input impedance of the circuit is

Z_{in} = \frac{V_i}{I_i} = \frac{Z}{1+A_v}.

If Z represents a capacitor with impedance Z = \frac{1}{s C}, the resulting input impedance is

Z_{in} = \frac{1}{s C_{M}} \quad \mathrm{where} \quad C_{M}=C (1+A_v).

Thus the effective or Miller capacitanceCMis the physical C multiplied by the factor (1+A_v).

Effects

As most amplifiers are inverting (i.e. A_v < 0), the effective capacitance at their inputs is increased due to the Miller effect. This can lower the bandwidth of the amplifier, reducing its range of operation to lower frequencies. The tiny junction and stray capacitances between the base and collector terminals of a Darlington transistor, for example, may be drastically increased by the Miller effects due to its high gain, lowering the high frequency response of the device.

It is also important to note that the Miller capacitance is the capacitance seen looking into the input. If looking for all of the RC time constants (poles) it is important to include as well the capacitance seen by the output. The capacitance on the output is often neglected since it sees {C}({1-1/A_v}) and amplifier outputs are typically low impedance. However if the amplifier has a high impedance output, such as if a gain stage is also the output stage, then this RC can have a significant impact on the performance of the amplifier. This is when pole splitting techniques are used.

The Miller effect may also be exploited to synthesize larger capacitors from smaller ones. One such example is in the stabilization of feedback amplifiers, where the required capacitance may be too large to practically include in the circuit. This may be particularly important in the design of integrated circuit, where capacitors can consume significant area, increasing costs.

Mitigation

The Miller effect may be undesired in many cases, and approaches may be sought to lower its impact. Several such techniques are used in the design of amplifiers.

A current buffer stage may be added at the output to lower the gain A_v between the input and output terminals of the amplifier (though not necessarily the overall gain). For example, a common base may be used as a current buffer at the output of a common emitter stage, forming a cascode. This will typically reduce the Miller effect and increase the bandwidth of the amplifier.

Alternatively, a voltage buffer may be used before the amplifier input, reducing the effective source impedance seen by the input terminals. This lowers the RC time constant of the circuit and typically increases the bandwidth.

Impact on frequency response

Figure 2 shows an example of Figure 1 where the impedance coupling the input to the output is the coupling capacitor CC. AThévenin voltage source VAdrives the circuit with Thévenin resistance RA. At the output a parallel RC-circuit serves as load. (The load is irrelevant to this discussion: it just provides a path for the current to leave the circuit.) In Figure 2, the coupling capacitor delivers a current jωCC( vi - vo ) to the output circuit.

Figure 3 shows a circuit electrically identical to Figure 2 using Miller's theorem. The coupling capacitor is replaced on the input side of the circuit by the Miller capacitance CM, which draws the same current from the driver as the coupling capacitor in Figure 2. Therefore, the driver sees exactly the same loading in both circuits. On the output side, a dependent current source in Figure 3 delivers the same current to the output as does the coupling capacitor in Figure 2. That is, the R-C-load sees the same current in Figure 3 that it does in Figure 2.

In order that the Miller capacitance draw the same current in Figure 3 as the coupling capacitor in Figure 2, the Miller transformation is used to relate CMto CC. In this example, this transformation is equivalent to setting the currents equal, that is

\ j\omega C_C ( v_i - v_O ) = j \omega C_M v_i,

or, rearranging this equation

C_M = C_C \left( 1 + \frac {v_o} {v_i} \right ) = C_C (1 + A_v).

This result is the same as CMof the Derivation Section.

The present example with Avfrequency independent shows the implications of the Miller effect, and therefore of CC, upon the frequency response of this circuit, and is typical of the impact of the Miller effect (see, for example,common source). If CC= 0 F, the output voltage of the circuit is simply Av vA, independent of frequency. However, when CCis not zero, Figure 3 shows the large Miller capacitance appears at the input of the circuit. The voltage output of the circuit now becomes

v_o =- A_v v_i = A_v \frac {v_A} {1+

Sound effect

For the album by The Jam, seeSound Affects.

Sound effects or audio effects are artificially created or enhanced sounds, or sound processes used to emphasize artistic or other content of films, television shows, live performance, animation, video games, music, or other media. In motion picture and television production, a sound effect is a sound recorded and presented to make a specific storytelling or creative point without the use of dialogue or music. The term often refers to a process applied to a recording, without necessarily referring to the recording itself. In professional motion picture and television production, dialogue, music, and sound effects recordings are treated as separate elements. Dialogue and music recordings are never referred to as sound effects, even though the processes applied to them, such as reverberation or flanging effects, often are called "sound effects".

Film

In the context of motion pictures and television, sound effects refers to an entire hierarchy of sound elements, whose production encompasses many different disciplines, including:

  • Hard sound effects are common sounds that appear on screen, such as door slams, weapons firing, and cars driving by.
  • Background (or BG) sound effects are sounds that do not explicitly synchronize with the picture, but indicate setting to the audience, such as forest sounds, the buzzing of fluorescent lights, and car interiors. The sound of people talking in the background is also considered a "BG," but only if the speaker is unintelligible and the language is unrecognizable (this is known as walla). These background noises are also called ambience or atmos ("atmosphere").
  • Foley sound effects are sounds that synchronize on screen, and require the expertise of a Foley artist to record properly. Footsteps, the movement of hand props (e.g., a tea cup and saucer), and the rustling of cloth are common foley units.
  • Design sound effects are sounds that do not normally occur in nature, or are impossible to record in nature. These sounds are used to suggest futuristic technology in a science fiction film, or are used in a musical fashion to create an emotional mood.

Each of these sound effect categories is specialized, with sound editors known as specialists in an area of sound effects (e.g. a "Car cutter" or "Guns cutter").

The process can be separated into two steps: the recording of the effects, and the processing. Sound effects are often custom recorded for each project, but to save time and money a recording may be taken from a library of stock sound effects (such as the famous Wilhelm scream). A sound effect library might contain every effect a producer requires, yet the timing and aesthetics of a tailor-made sound are often preferred.

Foley is another method of adding sound effects. Foley is more of a technique for creating sound effects than a type of sound effect, but it is often used for creating the incidental real world sounds that are very specific to what is going on onscreen, such as footsteps. With this technique the action onscreen is essentially recreated in order to try and match it as closely as possible. If done correctly it is very hard for audiences to tell what sounds were added and what sounds were originally recorded (location sound).

In the early days of film and radio, Foley artists would add sounds in realtime or pre-recorded sound effects would be played back from analogue discs in realtime (while watching the picture). Today, with effects held in digital format, it is easy to create any required sequence to be played in any desired timeline.

Video games

The principles involved with modern video game sound effects (since the introduction of sample playback) are essentially the same as those of motion pictures. Typically a game project requires two jobs to be completed: sounds must be recorded or selected from a library and a sound engine must be programmed so that those sounds can be incorporated into the game's interactive environment.

In earlier computers and video game systems, sound effects were typically produced using sound synthesis. In modern systems, the increases in storage capacity and playback quality has allowed sampled sound to be used. The modern systems also frequently utilize positional audio, often with hardware acceleration, and real-time audio post-processing, which can also be tied to the 3D graphics development. Based on the internal state of the game, multiple different calculations can be made. This will allow for, for example, realistic sound dampening, echoes and doppler effect.

Historically the simplicity of game environments reduced the required number of sounds needed, and thus only one or two people were directly responsible for the sound recording and design. As the video game business has grown and computer sound reproduction quality has increased, however, the team of sound designers dedicated to game projects has likewise grown and the demands placed on them may now approach those of mid-budget motion pictures.

Music

Some pieces of music use sound effects that are made by a music instrument or by other means. An early example is 18th century Toy Symphony. Richard Wagner in the opera Das Rheingold (1869) lets a choir of anvils introduce the scene of the dwarfs who have to work in the mines, similar to the introduction of the dwarfs in the 1937 Disney movie Snow White. Klaus Doldingers soundtrack for the 1981 movie Das Boot includes a title score with an sonar sound to reflect the U-boat setting.

Recording

The most realistic sound effects originate from original sources; the closest sound to machine-gun fire that we can replay is an original recording of actual machine guns. Less realistic sound effects are digitally synthesized


From Yahoo Answers

Question:

Answers:Digital cameras. A photon hits the sensor, liberating an electron which is then measured by the camera.

Question:albert einstein

Answers:When a light of suitable frequency is incident on a metal surface, electrons are emited from the metal surface this electrons are called photoelectrons and this phenomenon is called Photoelectric effect.

Question:Hello~ What's Albert Einstein's Photoelectric effect? I searched about it but I still dont have no idea ... Can u please explain it to me as if you r explaining it to a child ?? Thank You :)

Answers:OK lets see if i have it. at the quantum level, " small real small, the size of atoms" is when it takes place. 1st light is both a wave and a particle, that has been tested and proved. the wave is the "frequency or to our eyes the colour" of the light and the particle "photon" is the carrier of electromagnetic radiation, the energy of light "the warmth of the sun on your skin" its important to note that light is not one or the other but both called wave particle duality. now the Photoelectric effect imagine a steel plate, again at the quantum level "if you could you would see the individual atoms of the steel plate". the positively changed protons and the neutral charged neutrons at the centre with a cloud of negatively charged electrons surrounding them. now introduce light to the atoms. the protons from the light the ones that Cary the electromagnetic radiation "charge" smash into the atoms. Electrons can absorb energy from photons when irradiated. the energy from one photon is absorbed and used to liberate one electron from atomic binding. if an electron absorbs the energy of one photon and has more energy than the work function it get kicked out of the atom. its simple right. no its not. hoped this helped

Question:how does one calculate the threshold frequency for gases and solids, if any gas or liquid has a photoelectric effect? second, how does heating a metal or cooling a metal affect the threshold frequency concerning its photoelectric effect, if at all?

Answers:For gases, you don't get a well-defined work function, because the the absorption of light is by discrete lines: The only unique energy is the ionization energy, which is the energy required to lift an electron from the ground state to freedom. But then there are also the other energies, which lift the electron from the first/second/third/.. excited state to freedom; and these are smaller than the ionization energy. So there is no unique threshold. For solid conductors, the issue is the energy of the Fermi level, which is (more or less) the energy level at which the electrons have filled up to, bottom up. As the temperature increases, two things happen: the Fermi level rises a little bit; and electrons venture a little bit beyond the Fermi level. Both of these contribute to reducing the work function. For solid insulators, there is still the Fermi level, but in this case the level sits somewhere in a band gap. I guess what that means is that you have to dig up even more energy, to dig past the Fermi level down to the top of the buried conduction band: the work function has to include an even bigger "ransom" to buy out the electron.

From Youtube

Photoelectric Effect and Photoelectric Cell :Check us out at www.tutorvista.com The photoelectric effect is a phenomenon in which electrons are emitted from matter (metals and non-metallic solids, liquids or gases) as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light. Electrons emitted in this manner may be referred to as "photoelectrons".As it was first observed by Heinrich Hertz in 1887, the phenomenon is also known as the "Hertz effect", although the latter term has fallen out of general use. Hertz observed and then showed that electrodes illuminated with ultraviolet light create electric sparks more easily. The photoelectric effect takes place with photons with energies from about a few electronvolts to, in high atomic number elements, over 1 MeV. At the high photon energies comparable to the electron rest energy of 511 keV, Compton scattering, another process, may take place, and above twice this (1.022 MeV) pair production may take place. Study of the photoelectric effect led to important steps in understanding the quantum nature of light and electrons and influenced the formation of the concept of waveparticle duality. The term may also, but incorrectly, refer to related phenomena such as the photoconductive effect (also known as photoconductivity or photoresistivitity), the photovoltaic effect, or the photoelectrochemical effect which are, in fact, distinctly different. Photoelectric Cell : During the latter half of the ...

Photoelectric Effect :A gold leaf electroscope, a zinc plate and an ultra violet light. If the GLE is charged negative then by shining UV light on the zinc plate, it will discharge as a result of the wonders of the photoelectric effect. Worth a Noble prize any day.