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Unformatted text preview: Fig. 2: Voltage from drop magnet through coil Magnetic Induction Name: Teammates: Introduction We know that a current creates a magnetic field. This means that a moving charge acts on magnets (for example, current in a wire making a compass deflect). By applying Newton’s Third Law we can deduce that a magnet can apply a force on a moving charge. Therefore, if you position a magnet near a current-carrying wire that is free to move, the wire would move. This is, in fact, the basis for an electrical motor, where current-carrying wire coils are deflected around an axle when in presence of a magnetic field. In the previous paragraph, the movement of the charges is due to a potential difference. The question arises, what if the charges were being moved mechanically? Or what if the charges themselves were static, but the magnet was moved? As you will find out in this lab, the change in the magnetic field can cause the charges to move along the wire, thereby creating a current. This is the basis of an electrical generator. Induction In 1831, Michael Faraday was able to show that the induced electromotive potential is related to the rate at which the magnetic flux changed within a closed loop, is given by t N- emf ∆ ∆Φ = where Φ is the magnetic flux through one coil, and N is the number of loops. The flux is given by (refer to Figure 1) BAcos Φ = Faraday’s equation shows that the voltage induced in a the loop depends upon how quickly the magnetic flux through the loop changes. There are many ways to get the magnetic flux through a closed loop to change. In this experiment, we will do this by having a bar magnet, released from rest, fall freely along the central axis of a solenoid. The rate of change of the magnetic flux through the solenoid will be larger if the magnet is moving faster. Thus, we would expect the induced emf to be directly proportional to the speed of the magnet. If the magnet were to be dropped through a long solenoid, another effect will come into play. The current induced in the coils will in turn produce a magnetic field. This magnetic field tends to oppose the change in magnetic flux (this is again a manifestation of the law of conservation of energy.) This phenomenon is referred to as Lenz's law. This means that the falling bar magnet will feel forces other than that due to gravity. Fortunately, the effect of this magnetic force for the magnet and solenoid used in this experiment is small. Thus, the speed of the center of the bar magnet released from rest as it passes through the center of the solenoid is given by 2gh v = where h is the original height of the magnet above the solenoid and g is the gravitational field strength at that position....
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