electricity and magnetism

Quantitative investigation of magnetic braking

Mbraking1This project entailed an investigation of the magnetic damping of a metallic disk oscillating inside a nominally uniform magnetic field. It is well known that eddy currents form in loops and dissipate energy and slow the disk down. The aim of the current experiment was to deduce a quantitative relationship between the different parameters of the mechanical system and the magnitude of the damping force. Among the various parameters that influences the damping of the system, the most predominant was expected to be the size of the disk and the strength of the applied magnetic field. Using disks of varying sizes and using the same disks under varying magnetic fields, a relationship was deduced between the damping force and the magnetic field strength that agreed to a great extent with a proposed theoretical model.

By Azeem Iqbal | Physics Studio
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Measuring velocity by electromagnetic induction

Induction_velocity1This Studio project combined mechanics with electromagnetism. The e.m.f. induced in a set of vertically displaced coils as a magnet was thrown inside a cylindrical column was measured. The data was imported into a computer and speeds of the falling magnets were determined using two approaches. One was a naive approach determining speed from distance divide by transit time. The distance was the length of the coil. In a more accurate approach, however, we theoretically investigated the magnetic field due to a moving dipole inside a pickup coil. From this a mathematical model was derived which was fit onto experimentally determined curves, yielding accurate estimates of the velocities.Induction_velocity2

 

By Azeem Iqbal | Physics Studio
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Verifying Faraday’s law and electromagnetic damping

Faraday1In this experiment, an oscillatory system was employed for the verification of Faraday’s law. Disk magnets were attached with D-shaped metal disk which could oscillate through a fixed coil. Data was acquired using Lab Quest Mini that was attached with a voltage measuring sensor. The flux was obtained from numerical integration. Faraday’s law of electromagnetic induction was quantitatively verified. Fr magnetic damping, a resister which was placed across the coil allowing the flow of eddy currents. This experiment helped distinguish magnetic damping from usual damping oscillatory system due to air resistance. The maximum induced emf was plotted in both conditions (open and short) allowing a vivid comparison.

Steps in manufacturing the oscillating dee:

 

 

By Azeem Iqbal | Physics Studio
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Mutual induction and path dependent electric fields

This is a vivid demonstration of the concept of mutual inductance. A function generator and audio amplifier drive current through a homemade solenoid. The frequency range of interest is up to 20 KHz. Another piece of wire is wound around the solenoid, which picks up an induced emf. This emf is filtered and amplified. Both the primary and induced voltages are compared on an oscilloscope.
The real fun is when you see the induced emf grow as you keep on winding multiple turns of wire around the solenoid. You start unwinding or winding a few turns in the opposite sense, the induced emf starts to drop. When the same loop’s position is changed so that it does not enclose the primary solenoid, the induced emf drops again to zero. If the bunch of wires are placed vertically inside the primary, no emf is developed. Furthermore, change the frequency and notice the dependence of the induced emf. Last, the phase difference between the source and induced voltages is a clear demonstration of the time derivative of a sinusoid.


By Azeem Iqbal | Electricity and Magnetism
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Magnetic Braking

In this demonstration we exhibit the phenomena of magnetic braking. In the apparatus we have two metallic plates (one with slots), an electromagnet and a power supply. The metallic plate is a conductive surface which is oscillated in between an electromagnet. During this motion it will have circular electric currents called eddy currents induced in it by the magnetic field, due to Faraday’s law of induction. By Lenz’s law, the circulating currents will create their own magnetic field which opposes the field of the magnet. Thus the moving conductor will experience a drag force from the magnet that opposes its motion, proportional to its velocity and the plate gradually stops oscillating.

However, the metallic plate with slots experiences very less effects of the magnetic field and takes longer to come to a stop. This is because due to inconsistent surface it will not have circular electric currents and thus will not have the right magnetic field to oppose its movement against the field of electromagnet.

By Azeem Iqbal | Electricity and Magnetism
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Electromagnetic Induction

This demonstration exhibits the relationship between induced EMF and magnetic flux. In the apparatus, we have a rotating disk which has magnets placed on it, a Hall probe, and two solenoids with different number of turns. As the magnets are swept from beneath the sensors, the solenoids register the rate of change of flux while the Hall probe directly measures the flux. These variables are displayed on simultaneous graphs, all in real time.

Click here for the LabView code

By Azeem Iqbal | Electricity and Magnetism
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RC Circuit

In this demonstration we measure the voltages across the resistor and the capacitor to investigate the time needed to discharge a capacitor and determine the RC time constant of an RC series circuit. In the apparatus, we have an RC circuit, a data acquisition hardware and data displayed through a Labview program. We can see that when an alternating input voltage (on and off) is applied to the circuit, the capacitor gets charged and displays a gradual increase and decrease in the voltage.

Click here for the LabView code

By Azeem Iqbal | Electricity and Magnetism
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Barkhausen Effect

Discovered by German physicist Heinrich Barkhausen in 1919, the Barkhausen effect is a name given to the noise which a ferromagnetic material makes when the magnetic force applied to it is changed. To demonstrate this a coil of wire wound on the ferromagnetic material is affected by sudden, discontinuous jumps in magnetization using a hand held magnet. The sudden alterations in the magnetization of the material produces current pulse in the coil. This is amplified to produce a series of clicks in a loudspeaker; this is also called as Barkhausen noise. Similar effects can be observed by applying only mechanical stresses (e.g. bending) to the material placed in the detecting coil.

Barkhausen effect has many important applications today. For example, the amount of Barkhausen noise for a given material is linked with the amount of impurities, crystal dislocations, etc. and can be a good indication of mechanical properties of such a material. Therefore, it is used as a method of non-destructive testing for the degradation of mechanical properties in magnetic materials. It can also indicate physical damage in a thin film structure due to various nano-fabrication processes such as reactive ion etching.

By Azeem Iqbal | Electricity and Magnetism
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