La dualidad onda-partícula:

A partir de las investigaciones de Einstein y de Max Planck, se destruye la opsición tradicional entre materia y energía, puesto que ambas pueden ser interpretadas y estudiadas atrubuyendoles naturaleza corpuscular y ondulatoria.

Tradicionalmente se considera que la materia era discontinua y de naturaleza corpuscular (formada por partículas indivisibles o átomos); la energía, en cambio, se consideraba continua y de naturaleza ondulatoria. Contrariamente, según la física cuántica, tanto la materia como la energía se comportan como partículas y como ondas, hecho profundamente paradojal, ya que las propiedades corpusculares y ondulatorias son incompatibles.

En 1900, Max Planck descubrió  que la energía no se emite de manera continua, si no en “paquetes” o cuantos, de naturaleza discontinua. Poco después, Einstein identificaba los cuantos de la luz , a los que denominó fotones. Por otro lado, Louis de Broglie propuso que no solo los fotones, sino también los electrones se comportan como partículas y como ondas. Experimentos posteriores demostraron que, de hecho, todas las partículas materiales presentan un comportamiento ondulatorio.

En este punto, la ciencia abría un inesperado problema filosófico que solamente se acrecentó aún más: entonces, ¿Cómo es la realidad? Max Born respondía así: “La descrición corpuscular y la ondulatoria deben considerarse solamente como modos complementarios de imaginar un único proceso objectivo, pues está más allá de nuestro poder probar que sean realmente corpusculos o ondas”. De este modo, se cuestionaba, nuestra capacidad para acceder a la auténtica realidad. De hecho, tiempo después se custionaría incluso su existencia:

En consonancia con esta dualidad de la realidad, en el seno de la física cuántica se elaboraron dos teorías alternativas, pero equivalentes:

–Mecánica matricial de Werner Heisenberg: Esta formulación prefiere la interpretación de los procesos físicos, como procesos continuos de naturaleza corpuscular, ya que así son nuestras observaciones y el conocimiento que podemos tener de ellas.

–Mecánica ondulatoria de Schrödinger: Esta formulación prefiera la interpretación de los procesos físicos continuos y, por eso, destaca el comportamiento ondulatorio de la materia.

Estas teorías estaban basadas en el principio de incertidumbre, e de ellas se desprendían algunas consecuencias que resultaron desalentadoras, no sólo desde la perspecitva de la física clásica, sino mismo para científicos como Einstein que se resistían a aceptar implicaciones filosóficas sobre la realidad que generaba la nueva física.

Principio de incertidumbre:

La mecánica cuántica no puede establecer, simultaneamente y con precisión, la posición y la velocidad de una particula como el electrón. Una de las causas de esta imposibilidad es la inevitable interrelación entre el observador y el objeto observado, ya que no puede haber observación sin intervención del observador. Dicho de otro modo, toda medición implica una interacción entre el observador y el objeto observado, que altera las condiciones de este último. Esto ocurre en todos los casos: por ejemplo, al medir la temperatura del agua de una bañera, introducimos un termómetro que altera precisamente la temperatura que tratamos de medir. Este hecho, que en procesos cotidianos es imperceptible e irrelevante, se convierte en problemático cuando hablamos de fenómenos subatómicos, puesto que cualquier alteración, por mínima que sea, resulta significativa y determinante. Así, por ejemplo, para conocer exactamente la posición de un electrón, debemos iluminarlo con un fotón de luz, que al chocar con el modificará de manera imprevisible su velocidad.

La superposición cuántica:

Una de las consecuencias más sorprendentes de la mecánica cuántica se derivan de las ecuaciones de Schrödinger, que llegan a predecir que dos realidades diferentes y opuestas pueden llegar a superponerse simultaneamente. La teoría predice que, por ejemplo, si tomamos un naipe y lo colocamos sobre una mesa verticalmente y en equilibrio, la carta caerá simultaneamente de los dos lados. ¿Por qué razón en la vida cotidiana nunca observamos esta clase de superposiciones? La mayoría de los físicos considera que es el propio observador quién decide la observacioón en un sentido o en otro. Por lo tanto, en la realidad se dan los dos estados superpuestos, es decir, la realidad se encuentra indeterminada, pues se encuentra en todos los estados posibles al mismo tiempo, hasta que nuestra observación la obloga a determinarse y adoptar un estado o otro. El propio  Schrödinger fue uno de los primeros en darse cuenta de las sorprendentes consecuencias de su teoría, tal y como se pone de manifiesto en la paradoja conocida como El gato de Schrödinger.

-Implicaciones filosóficas:

Algunas implicaciones del modelo actual son las siguientes:

• Imposibilidad de separación sujeto-objeto: Según el principio de incertidumbre, para observar algo, hay que interaccionar con eso. Cuando el observado es de un tamaño suficientemente pequeño, esa interacción condiciona el resultado del experimento. Por lo tanto, la física cuántica llega a hablar de la creencia (procedente de la herencia griega) de que el mundo es una realidad objetiva que el ser humano puede llegar a conocer.
• Indeterminismo y ruptura de la casualidad: Desde la mecánica cuántica solamente se pueden  establecer leyes estatísticas que no predicen con exactitud el resultado de una observación, sino que tan solo calculan sus probabilidades. Un ejemplo de este indetreminismo es la la radiación  o la desintegración atómica que se produce espontáneamente y sin que haya una causa que la determine. Este hecho  viola el principio de casualidad, según  el cual todo fenómeno natural debe tener una causa exterior que lo produzca. Para algunos científicos, esta indeterminación  o sería un rasgo de nuestras leyes para describir la realidad, sino  una característica inherente a la realidad misma, que permanece indeterminada mientras no haya una observación que la obligue a decidir en un sentido o en otro.
• Alejamiento respecto al sentido común: La teoría de la relatividad y la física cuántica se distancian de nuestras intuiciones y percepciones habituales, por lo que resultan poco comprensibles para los que no son expertos. Contribuye a eso el hecho de que las nuevas teorías se apliquen, básicamente, en ámbitos cotidianos: en el macrocósmico y en los subatómico. Y es que, en el ámbito de la escala humana en el que nos movemos, siguen siendo válidas las leyes de la física clásica.

Generation of Sinusoidal Waveforms

In our tutorials about Electromagnetism, we saw how an electric current flowing through a conductor can be used to generate a magnetic field around itself, and also if a single wire conductor is moved or rotated within a stationary magnetic field, an “EMF”, (Electro-Motive Force) will be induced within the conductor due to this movement.

From this tutorial we learnt that a relationship exists between Electricity and Magnetism giving us, as Michael Faraday discovered the effect of “Electromagnetic Induction” and it is this basic principal that electrical machines and generators use to generate a Sinusoidal Waveform for our mains supply.

In the Electromagnetic Induction, tutorial we said that when a single wire conductor moves through a permanent magnetic field thereby cutting its lines of flux, an EMF is induced in it.

However, if the conductor moves in parallel with the magnetic field in the case of points A and B, no lines of flux are cut and no EMF is induced into the conductor, but if the conductor moves at right angles to the magnetic field as in the case of points C and D, the maximum amount of magnetic flux is cut producing the maximum amount of induced EMF.

Also, as the conductor cuts the magnetic field at different angles between points A and C, 0 and 90^o the amount of induced EMF will lie somewhere between this zero and maximum value. Then the amount of emf induced within a conductor depends on the angle between the conductor and the magnetic flux as well as the strength of the magnetic field.

An AC generator uses the principal of Faraday’s electromagnetic induction to convert a mechanical energy such as rotation, into electrical energy, a Sinusoidal Waveform. A simple generator consists of a pair of permanent magnets producing a fixed magnetic field between a north and a south pole. Inside this magnetic field is a single rectangular loop of wire that can be rotated around a fixed axis allowing it to cut the magnetic flux at various angles as shown below.

Basic Single Coil AC Generator

As the coil rotates anticlockwise around the central axis which is perpendicular to the magnetic field, the wire loop cuts the lines of magnetic force set up between the north and south poles at different angles as the loop rotates. The amount of induced EMF in the loop at any instant of time is proportional to the angle of rotation of the wire loop.

As this wire loop rotates, electrons in the wire flow in one direction around the loop. Now when the wire loop has rotated past the 180^o point and moves across the magnetic lines of force in the opposite direction, the electrons in the wire loop change and flow in the opposite direction. Then the direction of the electron movement determines the polarity of the induced voltage.

So we can see that when the loop or coil physically rotates one complete revolution, or 360^o, one full sinusoidal waveform is produced with one cycle of the waveform being produced for each revolution of the coil. As the coil rotates within the magnetic field, the electrical connections are made to the coil by means of carbon brushes and slip-rings which are used to transfer the electrical current induced in the coil.

The amount of EMF induced into a coil cutting the magnetic lines of force is determined by the following three factors.

• • Speed – the speed at which the coil rotates inside the magnetic field.
• • Strength – the strength of the magnetic field.
• • Length – the length of the coil or conductor passing through the magnetic field.

We know that the frequency of a supply is the number of times a cycle appears in one second and that frequency is measured in Hertz. As one cycle of induced emf is produced each full revolution of the coil through a magnetic field comprising of a north and south pole as shown above, if the coil rotates at a constant speed a constant number of cycles will be produced per second giving a constant frequency. So by increasing the speed of rotation of the coil the frequency will also be increased. Therefore, frequency is proportional to the speed of rotation, ( ƒ ∝ Ν ) where Ν = r.p.m.

Also, our simple single coil generator above only has two poles, one north and one south pole, giving just one pair of poles. If we add more magnetic poles to the generator above so that it now has four poles in total, two north and two south, then for each revolution of the coil two cycles will be produced for the same rotational speed. Therefore, frequency is proportional to the number of pairs of magnetic poles, ( ƒ ∝ P ) of the generator where P = is the number of “pairs of poles”.

Then from these two facts we can say that the frequency output from an AC generator is:

Where: Ν is the speed of rotation in r.p.m. P is the number of “pairs of poles” and 60 converts it into seconds.

Instantaneous Voltage

The EMF induced in the coil at any instant of time depends upon the rate or speed at which the coil cuts the lines of magnetic flux between the poles and this is dependant upon the angle of rotation, Theta ( θ ) of the generating device. Because an AC waveform is constantly changing its value or amplitude, the waveform at any instant in time will have a different value from its next instant in time.

For example, the value at 1ms will be different to the value at 1.2ms and so on. These values are known generally as the Instantaneous Values, or V_i Then the instantaneous value of the waveform and also its direction will vary according to the position of the coil within the magnetic field as shown below.

Displacement of a Coil within a Magnetic Field

The instantaneous values of a sinusoidal waveform is given as the “Instantaneous value = Maximum value x sin θ ” and this is generalized by the formula.

Where, V_max is the maximum voltage induced in the coil and θ = ωt, is the angle of coil rotation.

If we know the maximum or peak value of the waveform, by using the formula above the instantaneous values at various points along the waveform can be calculated. By plotting these values out onto graph paper, a sinusoidal waveform shape can be constructed.

In order to keep things simple we will plot the instantaneous values for the sinusoidal waveform at every 45^o of rotation giving us 8 points to plot. Again, to keep it simple we will assume a maximum voltage, V_MAX value of 100V. Plotting the instantaneous values at shorter intervals, for example at every 30^o (12 points) or 10^o (36 points) for example would result in a more accurate sinusoidal waveform construction.

Sinusoidal Waveform Construction

The points on the sinusoidal waveform are obtained by projecting across from the various positions of rotation between 0^o and 360^o to the ordinate of the waveform that corresponds to the angle, θ and when the wire loop or coil rotates one complete revolution, or 360^o, one full waveform is produced.

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From the plot of the sinusoidal waveform we can see that when θ is equal to 0^o, 180^o or 360^o, the generated EMF is zero as the coil cuts the minimum amount of lines of flux. But when θ is equal to 90^o and 270^o the generated EMF is at its maximum value as the maximum amount of flux is cut.

Therefore a sinusoidal waveform has a positive peak at 90^o and a negative peak at 270^o. Positions B, D, F and H generate a value of EMF corresponding to the formula e = Vmax.sinθ.

Then the waveform shape produced by our simple single loop generator is commonly referred to as a Sine Wave as it is said to be sinusoidal in its shape. This type of waveform is called a sine wave because it is based on the trigonometric sine function used in mathematics, ( x(t) = Amax.sinθ ).

When dealing with sine waves in the time domain and especially current related sine waves the unit of measurement used along the horizontal axis of the waveform can be either time, degrees or radians. In electrical engineering it is more common to use the Radian as the angular measurement of the angle along the horizontal axis rather than degrees. For example, ω = 100 rad/s, or 500 rad/s.

Radians

The Radian, (rad) is defined mathematically as a quadrant of a circle where the distance subtended on the circumference equals the radius (r) of the circle. Since the circumference of a circle is equal to 2π x radius, there must be 2π radians around a 360^o circle, so 1 radian = 360^o/2π = 57.3^o. In electrical engineering the use of radians is very common so it is important to remember the following formula.

Definition of a Radian

Using radians as the unit of measurement for a sinusoidal waveform would give 2π radians for one full cycle of 360^o. Then half a sinusoidal waveform must be equal to 1π radians or just π (pi). Then knowing that pi, π is equal to 3.142 or 22÷7, the relationship between degrees and radians for a sinusoidal waveform is given as.

Relationship between Degrees and Radians

Applying these two equations to various points along the waveform gives us.

The conversion between degrees and radians for the more common equivalents used in sinusoidal analysis are given in the following table.

Relationship between Degrees and Radians

The velocity at which the generator rotates around its central axis determines the frequency of the sinusoidal waveform. As the frequency of the waveform is given as ƒ Hz or cycles per second, the waveform has angular frequency, ω, (Greek letter omega), in radians per second. Then the angular velocity of a sinusoidal waveform is given as.

Angular Velocity of a Sinusoidal Waveform

and in the United Kingdom, the angular velocity or frequency of the mains supply is given as:

in the USA as their mains supply frequency is 60Hz it is therefore: 377 rad/s

So we now know that the velocity at which the generator rotates around its central axis determines the frequency of the sinusoidal waveform and which can also be called its angular velocity, ω. But we should by now also know that the time required to complete one revolution is equal to the periodic time, (T) of the sinusoidal waveform.

As frequency is inversely proportional to its time period, ƒ = 1/T we can therefore substitute the frequency quantity in the above equation for the equivalent periodic time quantity and substituting gives us.

The above equation states that for a smaller periodic time of the sinusoidal waveform, the greater must be the angular velocity of the waveform. Likewise in the equation above for the frequency quantity, the higher the frequency the higher the angular velocity.

Sinusoidal Waveform Example No1

A sinusoidal waveform is defined as: V_m = 169.8 sin(377t) volts. Calculate the RMS voltage of the waveform, its frequency and the instantaneous value of the voltage after a time of 6ms.

We know from above that the general expression given for a sinusoidal waveform is:

Then comparing this to our given expression for a sinusoidal waveform above of V_m = 169.8 sin(377t) will give us the peak voltage value of 169.8 volts for the waveform.

The waveforms RMS voltage is calculated as:

The angular velocity (ω) is given as 377 rad/s. Then 2πƒ = 377. So the frequency of the waveform is calculated as:

The instantaneous voltage V_i value after a time of 6mS is given as:

Note that the phase angle at time t = 6mS is given in radians. We could quite easily convert this to degrees if we wanted to and use this value instead to calculate the instantaneous voltage value. The angle in degrees will therefore be given as:

Sinusoidal Waveform

Then the generalised format used for analysing and calculating the various values of a Sinusoidal Waveform is as follows:

A Sinusoidal Waveform

In the next tutorial about Phase Difference we will look at the relationship between two sinusoidal waveforms that are of the same frequency but pass through the horizontal zero axis at different time intervals.