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05:26 IWF (Göttingen) German 2003

Trägheit des Magnetfeldes: Induktive Schaltverzögerung

The switching on and off of electric devices is usually characterized by their instantaneous response. The presence of inductors with large self-inductance can, however, cause considerable delays. Iron cores can lead to additional delays resulting from a change of the magnetization. Such delays, extending over minutes, will be shown here. A large copper spool is wound on a heavy closed iron core. It can be connected with a switch to a 2 volt accumulator (lead-acid battery) and a projection ammeter of short response time (less than 1 sec). The time is measured with a large, hand-operated (historic) stopwatch. These experiments always are extremely surprising, considering that we tend to associate electric phenomena with the idea of the instantaneous, the timeless.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
01:21 IWF (Göttingen) German 2003

Bestimmung des elektrischen Erdfeldes

The electric field of the earth will be determined. A parallel plate capacitor of area 1 m2 is attached to the end of a long bamboo pole. The capacitor is connected to a ballistic galvanometer calibrated to measure current pulses (charges). On a balcony outside the lecture hall, the capacitor is held with its plates horizontal.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
02:09 IWF (Göttingen) German 2004

Kapazität einer Kugel

Experimental determination of the capacitance of a sphere.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
07:36 IWF (Göttingen) German 2004

Stromlinien-Modellversuche

The goal is the demonstration of two-dimensional streamline patterns as they occur when non-viscous fluids flow around obstacles. The patterns shown are models, since they have been produced in a viscous fluid under conditions of laminar flow.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:59 IWF (Göttingen) German 2004

Maxwellsche Scheibe

A body that is being accelerated downward weighs less than when at rest. This is demonstrated with a flywheel on a shaft suspended on one arm of a household scale (Maxwell's disk). It is suspended on one arm of the scale with two strings which wrap around the thin shaft. When the flywheel is released, it accelerates downward, and the scale reads a reduced weight. During the subsequent rise (the flywheel still accelerating downward!) the scale again indicates a reduced weight.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
00:54 IWF (Göttingen) German 2004

Schwanke Achse

An object rotates stably around its axis of maximum moment of inertia, even if it is attached to a bent supple shaft. The experiment also shows that particles leave a rotating object by flying off in a tangential direction.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:27 IWF (Göttingen) German 2004

Elektrischer Wind

At sharp corners, even small voltages can lead to large electric fields. They can ionize the surrounding air, making it electrically conducting.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:22 IWF (Göttingen) German 2003

Zirkulare Schwingungen

Through superposition of the linear oscillations of two leaf springs of almost equal frequencies, linear, elliptic and circular oscillations can be generated and shown by optical projection.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
02:42 IWF (Göttingen) German 2004

Wirbelstrombremse

Forces are demonstrated which arise when an electric conductor moves through an inhomogeneous magnetic field.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
00:50 IWF (Göttingen) German 2004

Kräfte im elektrischen Feld

Between two surfaces separated only by a small gap, small voltages can lead to appreciable forces.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:22 IWF (Göttingen) German 2004

Seifenblasen im elektrischen Feld

The repulsive force between two bodies carrying charges of the same sign will be demonstrated.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
03:28 IWF (Göttingen) German 2004

Magnetischer Spannungsmesser

A long induction coil wound on a flexible hose is used to explore the magnetic field near current carrying conductors and also near a permanent magnet.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
03:10 IWF (Göttingen) German 2004

Induktion in bewegten Leitern

A conductor moving in a magnetic field experiences an electric field.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
03:04 IWF (Göttingen) German 2004

Induktion in ruhenden Leitern

A changing magnetic field generates an electric field.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:55 IWF (Göttingen) German 2004

Magnetisches Drehfeld

A rotating magnetic field results from the superposition of two magnetic fields oriented perpendicularly to each other, which vary sinusoidally with equal frequency, but with a phase difference, ideally of 90 degrees.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
02:28 IWF (Göttingen) German 2004

Elektromagnet

It will be shown that in a small electromagnet surprisingly large forces can be generated. However, these forces decrease drastically with the introduction of only a small gap between the pole faces.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:21 IWF (Göttingen) German 2004

Sphärische Aberration

The imaging error called "spherical aberration" is demonstrated by imaging a small coil of a light bulb.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:03 IWF (Göttingen) German 2004

Paramagnetische Materie

Paramagnetic matter gets pulled into regions of a large magnetic field. For the demonstration, liquid oxygen is poured into a shallow container placed in front of an electromagnet with non-parallel faces.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:33 IWF (Göttingen) German 2004

Induktionsläufer

Eddy currents induced in an aluminum disk in a moving inhomogeneous field tend to move the disk along with the field. This is the principle of the induction motor.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:48 IWF (Göttingen) German 2004

Reflexionskegel

The reflection of light is demonstrated using a polished steel tube. The reflected light has the shape of a cone.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
00:48 IWF (Göttingen) German 2004

Perspektive

Two-dimensional images of three-dimensional structures have a perspective, that is a certain ratio of size and distance for things which lie behind each other. The perspective depends on the position of the centers of the projection, which in imaging lie in the centers of the entrance- and exit-pupils. Using the images of two objects positioned at different distances from the imaging lens, the perspective and its changes will be shown.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:45 IWF (Göttingen) German 2004

Chromatische Aberration

Chromatic aberration occurs in imaging as result of the wavelength dependence of the index of refraction. It will be demonstrated on a special example.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
02:31 IWF (Göttingen) German 2004

Auflösungsvermögen

It is shown that in an optical image the individual light spots are diffraction patterns caused by the opening of the imaging lens. The resulting limit of the angular resolution is demonstrated with the aid of two pairs of holes with different separations.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
02:46 IWF (Göttingen) German 2004

Polarisiertes Licht

The plane of polarization of a light beam which has been polarized by passing it through a Nicol prism is made visible through scattering in a slightly milky liquid.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:16 IWF (Göttingen) German 2004

Krummer Lichtstrahl

A trough contains a sugar solution with a vertical concentration gradient, so that its index of refraction decreases with increasing height. A laser light beam enters the trough, tilted slightly against the horizontal direction. As it moves through the liquid, it is bent, as can be observed through scattering.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:58 IWF (Göttingen) German 2004

Astigmatismus

The imaging error called astigmatism occurs when light travels not parallel to the axis of the lens, but under an angle. Instead of image points, extended lines or streaks are formed.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
06:26 IWF (Göttingen) German 2004

Wasserwellenexperimente

Some of the fundamental properties of waves are demonstrated using surface waves in a water trough.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
00:40 IWF (Göttingen) German 2003

Langsam ablaufender elastischer Stoß

Elastic collision between two bodies in slow motion through the proper choice of the experimental conditions. It will be shown that during the collision the kinetic energy is briefly converted into potential energy and then back into kinetic energy. The slow collision, achieved through the proper choice of masses and spring constants, demonstrates clearly the transformation from kinetic to potential energy, and back again, as is characteristic for elastic collisions. This experiment also demonstrates the conservation of linear momentum.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
02:03 IWF (Göttingen) German 2003

Zur Vektornatur des Drehimpulses

A ventilator which can rotate freely around a vertical axis can be used to demonstrate that the angular momentum is a vector. A ventilator is mounted so that it can rotate freely around a vertical axis. It can also be tilted so that the air is blown either horizontally or upward. Upon turning on the ventilator, both the propeller and the driven air jet receive an angular momentum. Its vector points in the direction of the jet, parallel to the axis of the propeller. The ventilator receives an equal angular momentum in the opposite direction (opposite sense of rotation). The experiment is carried out for two different orientations of the ventilator.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
00:56 IWF (Göttingen) German 2003

Präzession eines rotierenden Rades

A spinning top (gyroscope) does not follow a torque in the same way as, for example, a top at rest. Rather, it moves sideways, it "precesses". This startling behavior will be shown here. The top is a bicycle wheel with its rim filled with lead wire. It can be suspended on a rope dangling from the ceiling. The wheel is spun while holding its axle horizontal. Then, one end of the axle is attached to the rope. The weight of the wheel and the tension in the rope together cause a torque which, however, does not turn the axle into the vertical position, as would happen if the wheel were not spinning. Instead, the axle, which indicates the direction of the wheels angular momentum, circles on a horizontal plane around the point on which it is suspended. This sideways motion of a top under the influence of a torque is called "precession".
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
02:42 IWF (Göttingen) German 2003

Drehstuhlexperimente zur Erhaltung des Drehimpulses

Conservation of angular momentum around the vertical axis of a rotating chair. A man sitting on a rotating chair with very little friction uses weights, a spinning wheel, and a wooden hammer with a long handle to demonstrate the vector nature of the angular momentum as well as its conservation in the absence of external torques. This setup allows to limit the observation to a single (the vertical) component of the angular momentum.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
02:25 IWF (Göttingen) German 2004

Rotation um freie Achsen

It will be shown that the axis of maximum moment of inertia is also the most stable axis of free rotation. For this, objects of different shapes are suspended on thin wires from the vertical axis of an electric motor, and are rotated at increasing frequencies. They are a cylindrical metal rod, a piece of wood in the form of an egg, and a loose loop of a metal chain.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:21 IWF (Göttingen) German 2003

Dynamische Stabilität einer Fahrradkette

Belts made of soft material which are flexible while at rest, in this case a chain made of metal links, can become quite rigid, independent of their shape, when their tangential velocity is sufficiently large. This phenomenon is called "dynamic stability". Through the radial forces the chain stiffens, and after it gets thrown off the toothed wheel, it roles along the floor, jumps over a wooden beam, and collapses into its shapeless form only after coming to rest on the rug after colliding with the wall. It is clearly seen how the stiff chain deforms somewhat as it hits the beam. Note also how long the chain continues to rotate on the rug near the end of the experiment, before it finally comes to rest and collapses.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
01:10 IWF (Göttingen) German 2004

Freie Rotation eines quaderförmigen Körpers

Only the axes of maximum and minimum moment of inertia are free axes of rotation around which a body can rotate stably without mechanical support. Attempts at rotation around other axes lead to wobbling, i.e. unstable rotation. A piece of styrofoam in the form of a parallelepiped (like a cigar box) is thrown into the air while giving it a spin. In order to watch the motion, opposing surfaces have been marked with different colors.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:28 IWF (Göttingen) German 2004

Modell einer fortschreitenden Welle

The connection between circular motion, phase difference and wave propagation is shown with the help of a series of beads arranged to form a right-handed helix.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
00:44 IWF (Göttingen) German 2003

Impulserhaltungssatz

According to the law of the conservation of momentum, which states that in every closed system the sum of the individual momenta stays constant. They can be exchanged inside the system. Three examples will be shown. In all three cases, the total momentum of the closed system remains constant.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
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