Coil_Experiment

Aim: To determine the effect of relative motion between the coil and the magnet is on the induced current (Prac 1) Hypothesis: The faster the movement between the coil and the magnet, the more current will be produced. Equipment: * coil * centre-reading Galvanometer * Bar Magnets * Connecting Wires x2 * Alligator clips x2 Method: 1. Collect equipment and set it up like shown in fig. 1 making sure that the galvanometer is connected to the coil with 2 wires. 2. Hold a magnet stationary inside of the coil and observe the movement of the Galvanometer and record in a table. 3. Push the North Pole of the magnet back and forth into the coil at a slow speed and record the amount of current produced in the galvanometer. 4. Repeat steps 3 again but alter the speed of the magnet entering the coil to medium constant speed t and then again with a fast constant speed by altering the movement of the hand 5. Repeat the experiment three times to achieve consistent results, avoiding outliers and take the averages of results. Fig.1 – setting of the equipment | Results: Current produced by pushing one magnet bar 7.5cm inside the coil Speed of the relative motion (movement of magnet) | Current produced (µA) | | Trial 1 | Trial 2 | Trial 3 | Average | stationary | 0 | 0 | 0 | 0 | slow | 2 | 2 | 2 | 2+2+2/3 = 2 | medium | 14 | 16 | 15 | 14+16+15/3 = 15 | fast | 32 | 28 | 30 | 32+28+30/3 = 30 | The results show that the relative motion of the magnet to the coil has an effect on the generated electric current. The faster the motion of the magnet bar, the higher the electromotive force resulting in a higher induced current. Looking at the results, the highest current produced is from the relative speed that is fast which produced 30 µA. The lowest current produced was when the relative speed was slow which produced 2 µA. The medium relative motion of the magnet produced an average 15 µA. Therefore the results support the hypothesis which states that the faster the movement between the coil and the magnet, the more current will be produced. Whether the coil moves or the magnet does not affect the change the experiment or the current produced as long as there is relative movement. When the magnet is stationary, no current is produced no matter where it is located. Also, when pulling the magnet out of the coil, the amount of current produced does not change but only the direction of the current changes. The results also show that no current is induced when the magnet is stationary. For current to produce either the coil or the magnet must move. Of both are stationary, no current is produced. This is given by the results in which the stationary magnet did not produce any current for the trials. Discussion: There is no current induced when the magnet is stationary. When the magnet is moved at a slow speed, low current is produced but when the magnet is moved master, more current is produced which showed that the higher the speed of the motion between the magnet and the coil, the more current is induced. The faster magnet induces more current because a faster movement cuts more flux lines per second resulting in a higher current which also means that the faster magnet bar travels a small duration of time which means that more flux lines are cutting at a shorter time which results in more current being produced as it takes a shorter time to cut the same number of flux lines. The flux density is therefore higher when the relative motion is faster so more flux lines are cut. Relative motion between magnet and coil produces current as there is a change in flux. Greater the change in flux, greater EMF / current produced. The results show that the induced current depends on the speed at which the magnet is moving towards or away from the coil. Other thing that had been learnt is that it is not important whether the magnet is moved or the coil as long as one of them is moved relative to the other. The current induced flows back and forth when the magnet is pulled in and out of the coil, therefore it is produces AC current. Other variables which were not testable with this experiment include effect of the number of turns in the coil because the same coil was used each time for all the trials. To test this, the number of turns in the coil should be varied; however, this is not necessary because the experiment was aimed to determine the effect of the direction of distance between the coil and the magnet, the strength of the magnet and the relative motion. Suggested improvements: Accurate equipment was used such as the galvanometer which gave accurate reading of current measured in small units of µA. However, there were also errors which contributed to receiving inaccurate results such as human error. The magnet was moved using the movement of the hand. This prevented from having a constant speed throughout the experiment because the human reflexes slowed the magnet as it reached closer to the coil; therefore constant speed was not maintained. The same person was used all the time to move the magnet so that the speed was relatively the same but this did not make a big difference to the end results. Hence the maximum deflection on the galvanometer was read. The independent variable was the relative motion between the coil and the magnet because the effect of the motion of the magnet was being tested. The dependent is the amount of current that was induced. The other factors that were controlled to make the experiment more valid included: * The distance between the coil and magnet: this is a factor which contributes to producing more current therefore if the distance is not controlled and the same throughout the experiment, the results could alter which gives inaccurate results. * Same magnet was used: different types of magnet had different magnetic strength which is another variable which alters the amount do current produced. As a result it is essential that the same magnet is used so that the magnetic strength is the same and only one magnet was used. The same galvanometer and coil as well as magnet were used to eliminate any invalidity which could alter the results. The same coil was used because the number of turns in the coil affects the current produced. More coils means more current so this obtains validity. The same wires were used as well because the diameter of the wire is a factor that affects the current induced. * The type of coil and the number of turns of coil has an effect on the magnitude of EMF produced. By using the same coil with the same number of turns, the experiment is valid. The cross diameter of the coil also effects the induced current so by using the same coil the experiment is kept more valid. * The magnetic flux differ at different temperature so the magnet and room temperature should be kept constant. * The same end of the magnet was used for all the trials which was the North Pole side. * ruler to maintain the same distance between the magnet and the coil To improve the experiment, better and new equipments should be used. To eliminate the human error which is major in this experiment, mechanical equipment should be used to perform the same job. A digital ammeter accurate to 3 significant figures should be used which allows a more accurate instantaneous result. A remote controlled wheeled apparatus that travels in a straight path which can carry the magnet should be used as this would give a constant speed and travel in a straight line. A speedometer could be used to maintain the speed of magnet as it travels towards and inside the coil. This will give more accurate reading of the galvanometer and if it is digital, automatic reading of micro amp will be given which eliminates the human error in reading the position of the needle in the galvanometer to determine current. Other method of finding induced currents can be performed to obtain results which could be compared with the method performed above such using a hand wound DC meter connected to a voltmeter. By spinning the DC motor, the coil moves within a magnetic field and cuts the flux lines as it spins, producing current. To get a better reading of the current induced, a galvanometer sensor which can be connected to the laptop can be used. This will give a reading accurate to two decimal places because the computer digitally shows the induced current which eliminates the human error in determining the amount of current induced. Conclusion: The experiment show that the current produced is affected by the relative motion between the magnet and the coil. The results obtained clearly show that more current is produced when the relative motion between the coil and the magnet is faster. The faster the movement between the coil and the magnet, the more the current will be produced. Therefore, the experiment supported the hypothesis. Aim: to determine the effect of the magnetic strength the induced current (Prac 2) Hypothesis: The stronger the magnetic field strength, the more current will be produced. Method: 1. Collect equipment from the equipment tray and place it on the working bench. 2. Connect one end of the 2 wires to the galvanometer and the other end to the coil using 2 alligator clips, making a complete circuit like shown in fig 1. (prac 1) 3. Push the North Pole of the magnet 7.5cm into the coil at a slow constant speed and record the amount of current produced in the galvanometer. 4. Repeat step 3 using 2 magnet bars making sure that both of the magnets enter the coil from the North Pole end. 5. Repeat experiment three times to achieve consistent results, avoiding outliers and take the averages of results.7.5cm Magnet Results: Current produce at medium speed at 7.5cm inside the coil Number of Magnets | Current produced (µA) | | Trial 1 | Trial 2 | Trial 3 | Average | 1 | 15 | 16 | 14 | 15+16+14/3 = 15 | 2 | 32 | 30 | 34 | 32+30+34/3 = 30 | The results obtained from the experiment show that the strength of the magnet affects the amount of current produced. As shown by the results, the higher the magnetic strength is, the more the current will be produced. By looking at the results, when two magnets were used, the average current produced was 30µA which is double the current produced when only one magnet was used which produced 15 µA. The experiment does not suggest however, that by double the magnetic field, double the current was produced because the experiment was not performed to investigate this. The experiment was performed to determine whether the strength of the magnet had an effect on the current produced which was obtained from the experiment. Magnetic flux is the name given to the amount of magnetic field passing through a given area. The strength of a magnetic field is also known as the magnetic flux density. Current is produced when these flux lines are cut by the magnet. When there is more magnetic strength, more reflux lines are cut which results in more current being produced. The hypothesis was supported as the results indicate that more current was produced with a stronger magnetic field strength. Discussion: Since the experiment is determining the effect of strength on the induced current, the independent variable is the magnetic field strength which was varied by using more magnets for more magnetic field strength. The variables that were kept the same throughout the experiment were using the same coil, the same wires, the room temperature and the same galvanometer (for the reason mentioned in prac.1). The controlled variable was keeping the distance between the coil and the magnet the same for all trials and also putting the magnet 7.5cm inside the coil so that accurate results were established and the relative speed of the magnet as it was moved toward the coil which was kept at a constant slow rate. The dependent variable was the amount of current induced. All the others variables are controlled to make experiment valid. (Refer to prac 1). The results show that the faster the motion of the magnet bar the higher the electromotive force resulting in a higher induced current, this is independent on whether the coil moves or the magnet as long as there is relative movement and it is also independent of the direction of the magnet bar as withdrawing it will only give the opposite current flow. The results suggest that if the magnet is stationary there is no current produced as shown by the Galvanometer which read zero when the magnet was stationary inside the coil. There was no current produced either when the coil was moved while the magnet was inside it because the movement was not relative to each other. Pushing the magnet bar into the coil induces current determined by the deflection of the needle in the Galvanometer. When the North Pole of the magnet enters the Galvanometer, the flow of current is anticlockwise. When the magnet is pulled out of the coil, the needle in the Galvanometer deflects backward which indicates that current is still produced but the direction of the current had changed. Current is still produced if the circuit is not complete, however, if the Galvanometer is not connected to the coil, the current produced cannot be detected. When a magnet is being pushed into a coil, the magnet cuts the field lines which induce EMF and if there is a circuit, current will flow. When the circuit is not complete, current still get produced by the moving of magnet inside the coil, however, the magnitude of the induced current cannot be calculated due to the break in the circuit. When the magnet was being pushed into the coil, an opposing force was experience but this was very weak. This was produced by the current induced in the coil, creating a magnetic field which repels the force applied by the hands to push the magnet. Conclusion: By performing this experiment, it was determined that the strength of the magnetic field has an effect on the current induced. The hypothesis was supported because the experiment showed that the faster the relative motion is, the higher the EMF production, therefore more current is produced, resulting in a higher reading in the galvanometer. Aim: To investigate the effect of distance between the magnet and the coil on the induced current. (Prac 3) Hypothesis: The closer the magnet is to the coil, the more current is produced therefore the galvanometer will produce a higher reading. Method: 1. Set the apparatus like shown in fig.1 2. Mark a distance of 25cm from the coil to the position of the magnet. This will be kept constant for all the trials. 3. Push the North pole of the magnet from the 0cm to the 25cm position of the ruler as shown below: 4. Observe needle on the galvanometer to determine how much current is produce and write in a table. 5. Move the ruler 5cm so that the distance between the coil and the magnet is 30cm. 6. Push the magnet from the 0cm to the 25cm with a slow constant speed and record the value for the current produced in the Galvanometer. 7. Move the ruler 5cm more so that the distance between the coil and the magnet is 35cm. 8. Push the magnet from the 0cm to the 25cm with a slow constant speed and record the value for the current produced in the Galvanometer. 9. Place the magnet on top of another ruler and mark 7.5cm and slide the ruler on the bench 7.5cm toward the coil as shown below: 10. Push the ruler with the magnet inside the coil with a slow constant speed until the magnet goes into to the coil 7.5cm and record the value for the current produced in the Galvanometer. 11. Repeat experiment 3 times to achieve consistent results, avoiding outliers and take the averages of results. Results: Current produced using one magnet bar at constant slow speed Distance from edge of coil (cm) | Current produced() | | Trial 1 | Trial 2 | Trial 3 | Average | -7.5 | 29 | 28 | 30 | 29+28+30/3 =29 | 0 | 4 | 6 | 5 | 4+6+5/3 =5 | 5 | 2 | 2 | 2 | 2+2+2/3 =2 | 10 | 0 | 0 | 0 | 0 | The results indicate that the distance of the coil does alter the amount of induced current. The first measurement of distance -7.5cm from the coil indicates that the magnet enters 7.5cm into the coil. This produces an average 29 µA which has produced the most amount of current. The reason for this is because the distance between the coil and the magnet is minimal; in fact, the induced current is high because the magnet is moving inside the coil which eliminates distance between the coil and magnet, distance being one of the factors that decreases the amount of current being produced. When the distance from the edge of the coil to the magnet is zero, average current of 5µA is produced which is a lower current. Similarly, when the magnet is 5cm away from the edge of the coil, smaller amount of only 2µA is produced while at the distance of 10cm away from the edge of the coil, no current was detected. The results show that the higher the distance between the magnet from the coil, the less current that is produced. This clearly show that distance is a factor that affects the amount of current produced because the least distance gap produced the most current and less current was produced when the distance between the magnet and the coil was larger. Discussion: In determining the effect of the distance between the coil and the magnet on the current induced, the independent variable is the distance of the magnet from the coil while the dependent is the amount of current induced as shown by the Galvanometer. The direction of the generated electric current changes when the direction of the relative motion between the coil and the magnet is reversed. Similarly, the direction of the generated electric current changes when the polarity of the magnet is reversed however, reversing the magnet or coil does not change the magnitude of the current produced. The magnitude of the generated electric current increases as the speed of the relative motion between the coil and the magnet is increased. The coil has to be relatively close to the magnet in order for current to be produced. The reason that more current is produced when the magnet is closer to the coil is that an electric current flowing in a wire creates a magnetic field around the wire, the field lines are cut by the magnet which induced EMF which as a result indices current. the closer the magnet to the coil, the more flux lines are cut which results in more current being induced. When the magnet and the coil are stationary, no current is induced no matter where the position of the magnet is. Two rulers were used, one attached to the magnet and the other next to the coil. This was so that a fixed length of magnet entered the coil. This way, errors were eliminated because if the magnet enters further into the coil, the magnitude of the induced rate could have been affected. This was not experimented though by the investigation. It was also observed that the when the magnet was placed outside the coil, no current was produced. This is because the flux density outside the solenoid is zero; therefore no current is produced because there are no flux lines for the magnet to cut through. Magnetic field lines only exist as loops; they cannot diverge or converge to a point like electric field lines. Conclusion: The distance of the magnet from the coil determines how much current is produced. The results show that the closer the magnet is to the coil, the more current is produced which is determined by the needle deflection of the Galvanometer. Therefore, the hypothesis is supported. Aim: to investigate how to predict the direction of the induced current inside a coil. Hypothesis: The direction of the induced current in the coil can be predicted using the Right Hand rule. Method: 1. Position fingers and thumb like shown in fig.1 2. Using the right-hand, curl the fingers into a half-circle around the wire 3. Point the thumb in the direction of the induced magnetic field within the coil. 4. Trace the direction of the curl of the fingers holding the coil 5. Determine the direction of the induced current in the coil which is determined by the direction of the curl of the finger. Fig.1 How to determine direction of induced current   Results: By learning and performing how to use the right-hand rule, the direction of the induced current was determined. Exercises from text books were completed to practice the skill of using the right-hand rule to determine the direction of the induced current in a coil and the answers were checked to see if the predicted directed of the induced current. The hypothesis stated that the direction of the induced current can be calculated using the right-hand rule which was supported by the method used to calculate the induced current inside the coil. This method of predicting the direction of the induced current in the coil is the same regardless of each variable. Direction of induced magnetic field within the coil | Direction of induced current flow using the right hand rule | | By positioning the thumb of the right hand to the direction of the induced magnetic field, the curl if the fingers determine the direction of current flow. | | | | | Discussion: Electromagnetic induction is the creation of an emf in a conductor when it is in relative motion to a magnetic field or it is situated in a changing magnetic field. This is known as induced emf. In a closed circuit, the emf allows current to be produced which is called induced current. Faraday demonstrated that it is possible to produce current in a coil by using a changing magnetic field. For a current to flow through the galvanometer, there must be electromotive force (emf). The magnitude of the current depends on the resistance of the circuit and the magnitude of the emf generated in the circuit. When the magnet or coil is moving it causes a change in the magnetic field around the coil, current is induced. Thus Michael Faraday concluded that a current will be induced in a coil when there is a change in the magnetic field around it, which is achieved when there is relative movement between the magnet and the coil. It is important to note that the factors that was investigated which can increase the size of the induced current by: * Increasing the speed of the relative motion between the coil and the magnet * Increasing the strength of the magnetic field * Increasing the number of turns in the coil Lenz discovered a way to predict the direction of an induced current. This method is given the name ‘Lenz’s Law’. His law states: “An induced current emf always gives rise to a current that creates a magnetic field that opposes the original change in flux through the circuit. When determining the direction of the induced current, it is useful to use the field line method for representing magnetic fields.” As the magnet approaches the coil, the magnetic flux density within the coil increases. The induced current sets up a magnetic field that opposes this change. The approaching magnet towards the coil increases the number of field lines that pass through the coil. The induced current in the coil produces field lines that point to the opposite direction to counter the increase. When the north pole of the magnet moves towards the coil, the induced EMF produced resulting in induced current flows in the anti clockwise direction. This makes the coil a magnetic north pole with line of force coming out of the coil. As the N-pole of the magnet moves towards coil, the magnetic flux linking the coil increases.. Therefore, an emf and hence current is induced in the coil according to faraday's laws of electromagnetic induction. The north pole from the coil opposes the onward approach of the N-pole from the magnet. The magnets repel each other because like poles repel each other. The mechanical energy provided by the force of the hand when the magnet is pushed inside the coil is converted to electrical energy in order to overcome the repulsion force between the magnet and the coil. When magnet is moved away from the coil, more current is produced due to the movement of the magnet which cuts the flux line resulting in the production of current. However, as demonstrated by the Galvanometer, the direction of the current changes. The same magnitude of current is produced whether the magnet is push or pulled from the coil, only direction changes to the clockwise direction. The polarity of the coil changes from the north pole to south pole which had lines of force entering. There is an attraction force between the north pole of the magnet and the south pole of the coil which forms a resistance to the motion of withdrawal. The mechanical energy required to overcome the force of attraction is converted in to electric energy. When the magnet bar is stationary, the induction of current is stopped. If the south pole of the magnet is inserted into the coil, the direction of the current is reversed. This will result in the direction of the induced current flow to be clockwise because the coil would have a magnetic south pole. Like before, south poles repel each other. The mechanical energy provided by the hands is converted to electrical energy to overcome the repulsion forces. Similarly, moving the magnet away from the coil causes the coil to be a magnetic north pole which attracts the moving away magnet. The induced current will flow in an anti’clock wise direction. Therefore, as stated in Lenz’s law, the induced current will flow in such a direction as to oppose the cause that produces it. Law of conservation of Energy: Lenz’s Law is possible due to the law of conservation of energy. Energy cannot be created or destroyed but only transformed into other forms. Faraday's ideas about conservation of energy led him to believe that since an electric current could cause a magnetic field, a moving magnetic field should be able to produce an electric current. The magnet inside the coil producing current does not mean that current is being produced from nowhere. Because energy is conserved, it must mean that a different form of energy must have been converted to induce current. To overcome the magnetic repulsion between the like poles, work must be done work must be done to push the magnet against the repulsive force. This work is provided by the arms which has mechanical energy that is converted to electrical energy which can further be converted to heat energy if the current flows in a closed circuit. The same process occurs when the magnet is moved away from the coil except the direction of the current changes. If there was no force opposing the magnets movement, then the magnet could enter the coil at high constant velocity with no pushing forces acting which would require no work. This would mean that the heat energy produced would appear from nowhere which would have contradicted the law of conservation of energy. However, this is not what happens. Conclusion: Using the right-hand Rule, the direction of the induced current is determined when the direction of the induced magnetic field within the coil is given or determined using lenz’s law. Therefore the hypothesis was supported.