Understanding Magnetic Fields and Electromagnetic Induction Lab

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Physics

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Feb 20, 2024

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Lab 2: General Magnetism and Electromagnetic Induction Name: Group 5: Esteffy Velasco, Joshua VIllarreal, Marissa Zuniga, Evelyn Yanez Background of the Lab : Magnetic Fields and Magnetic Field Lines : Einstein is said to have been fascinated by a compass as a child, perhaps musing on how the needle felt a force without direct physical contact. His ability to think deeply and clearly about action at a distance, particularly for gravitational, electric, and magnetic forces, later enabled him to create his revolutionary theory of relativity. Since magnetic forces act at a distance, we define a magnetic field to represent magnetic forces. The pictorial representation of magnetic field lines is very useful in visualizing the strength and direction of the magnetic field. As shown in Figure 1, the direction of magnetic field lines is defined to be the direction in which the north end of a compass needle points. The magnetic field is traditionally called the B-field . Figure 1. Magnetic field lines are defined to have the direction that a small compass point when placed at a location. (a) If small compasses are used to map the magnetic field around a bar magnet, they will point in the directions shown: away from the north pole of the magnet, toward the south pole of the magnet. (Recall that the Earth’s north magnetic pole is really a south pole in terms of definitions of poles on a bar magnet.) (b) Connecting the arrows gives continuous magnetic field lines. The strength of the field is proportional to the closeness (or density) of the lines. (c) If the interior of the magnet could be probed, the field lines would be found to form continuous closed loops. Small compasses used to test a magnetic field will not disturb it. (This is analogous to the way we tested electric fields with a small test charge. In both cases, the fields represent only the object creating them and not the probe testing them.) Figure 2 shows how the magnetic field appears for a current loop and a long straight wire, as could be explored with small compasses. A small compass placed in these fields will align itself parallel to the field line at its location, with its north pole pointing in the direction of B . Note the symbols used for field into and out of the paper.

Figure 2. Small compasses could be used to map the fields shown here. (a) The magnetic field of a circular current loop is similar to that of a bar magnet. (b) A long and straight wire creates a field with magnetic field lines forming circular loops. (c) When the wire is in the plane of the paper, the field is perpendicular to the paper. Note that the symbols used for the field pointing inward (like the tail of an arrow) and the field pointing outward (like the tip of an arrow). Magnetic field is a way of mapping forces surrounding any object that can act on another object at a distance without apparent physical connection. The field represents the object generating it. Gravitational fields map gravitational forces, electric fields map electrical forces, and magnetic fields map magnetic forces. Extensive exploration of magnetic fields has revealed a number of hard-and-fast rules. We use magnetic field lines to represent the field (the lines are a pictorial tool, not a physical entity in and of themselves). The properties of magnetic field lines can be summarized by these rules: 1. The direction of the magnetic field is tangent to the field line at any point in space. A small compass will point in the direction of the field line. 2. The strength of the field is proportional to the closeness of the lines. It is exactly proportional to the number of lines per unit area perpendicular to the lines (called the areal density). 3. Magnetic field lines can never cross, meaning that the field is unique at any point in space. 4. Magnetic field lines are continuous, forming closed loops without beginning or end. They go from the north pole to the south pole. The last property is related to the fact that the north and south poles cannot be separated. It is a distinct difference from electric field lines, which begin and end on the positive and negative charges. If magnetic monopoles existed, then magnetic field lines would begin and end on them. Learning Goals : After completing this lab, students will be able to: a) Predict the direction of the magnet field at different locations around a bar magnet and an electromagnet. b) Compare and contrast bar magnets and electromagnets. c) Identify the characteristics of electromagnets that are variable and what effects each variable has on the magnetic field’s strength and direction. d) Relate magnetic field strength to distance quantitatively and qualitatively e) Explain practical applications of Faraday’s Law f) Explain what the cause of the induction is , Directions: Use the simulation the link https://phet.colorado.edu/en/simulation/legacy/faraday to complete this lab.

Activity 1: Bar Magnet Tab – General Magnetism 1. Click on the Bar Magnet Tab and you should see a bar magnet and compass on the screen. Please note that the color red refers to North and white refers to South. Place the compass at the North end of the bar magnet and observe which way the “red tip” of the compass points. Move the compass to the South end and observe where the “red tip” of the compass points. What can you say about where the north (red) tip of a compass points? When the compass is placed at the north end of the bar magnet, its red tip points north; when it is placed at the south end of the bar magnet, it points south, and its light tip points north. 2. Use your response to #1 to explain why the geographic north pole is the magnetic south pole. The geographic north pole is the magnetic south pole because the magnetic south is drawn to the north pole and the magnetic north is drawn to the south. Activity 2: Pickup Coil Tab – General Electromagnetic Induction 3. Set the number of loops to “1” and loop are to 50% and note what happens to the light bulb when The magnet is not moving and is not in the loop – The light bulb is off. The magnet is moving and is not in the loop – The light bulb turns on slightly. The magnet is not moving and is in the loop – The light bulb is off. The magnet is moving and is in the loop - The light bulb is on. 4. Does the speed of the magnet affect your results to #3? If so, describe how. Yes, I noticed when you move the magnet faster the light bulb gives off more light and if you move it slower the light bulb still gives off light but not as much. 5. Increase the number of loops to “3” and see if it affects your results from #3. If so, describe how. Yes, The lightbulb is still off if you don't move the magnet. There was a change in the brightness of the light bulb when you moved the magnet. When there was only one loop, moving the magnet slowly barely showed any light but with three loops it showed the amount of light if you moved it fast with 1 loop. 6. Increase the loop area to “100” and see if it affects your results from #3. If so, describe how. Yes, When moving the magnet through the loops, the brightness does seem to be brighter and bigger. Activity 3: Electromagnet Tab – Is Electromagnetism Reversible ? 7. You should see a battery attached to a loop of coil (an electromagnet) and a compass on the screen. Move the electromagnet around the screen and describe what the compass does.

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The north end of the compass contacts the left side of the electromagnet, which is on the south side, and the north end goes in the same direction as the electromagnet. 8. Move the compass around the electromagnet in order to determine the North and South poles. Draw a picture and label the North and South Poles. 9. Change your current source from DC to AC and describe what the compass does. When the current is switched to AC, we see that the compass begins to move from side to side. In DC, the compass is orientated in a straight line, which results in a high frequency and the compass being at the North Pole. 10. Observe the electrons in the AC current source and compare their movement to those in the DC current source. Explain the difference between DC and AC in terms of electron movement. When the electrons in an AC system are moving side to side, we can observe that the compass flips poles, but when the electrons in a DC system are in a solid state, the compass stays stable. Activity 4: Transformer Tab – Can We Use Electromagnetism? (You can take the electromagnet all the way to inside the coil) 11. The last tab showed us that current can create a magnetic field. Can this magnetic field generate electricity? That is, can we use electricity to generate more electricity? Move the electromagnetic back and forth and note what happens and Attach the PrtScn here = When we move the electromagnet back and forth the light bulb turns on, if the electromagnet is still the lightbulb is turned off.

12. Can electricity be used to create more electricity? Explain how. = Yes, for example, electricity may be created when the current changes in a magnetic field using AC voltage coil, when the current changes so does the magnetic flux thus creating an electromagnetic field and creating a current. 13. Change to an AC source. Note what happens while the electromagnet is not moving. Why does the light bulb light up? Do the electrons in the light bulb move as fast as the AC source? = When using an AC current source the light bulb will turn on even if the the electromagnet is not moving. The lightbulb’s electrons move slowly in comparison to the electromagnet electrons. Activity 5: Generator Tab – Putting it All Together 14. Turn on the water faucet and describe what happens and Attach the PrtScn here below. The light bulb's brightness rises and falls in proportion to the water flow's tempo.

Conclusion Magnetism : As you answer the questions on Magnetism and Electromagnetic Induction, explain in your own words why your answer makes sense and provide evidence from your Magnetism and Electromagnetic Induction experiment. Add more experiments to Magnetism and Electromagnetic Induction if you need to get better evidence. After testing and making certain observations of our work, we have, agreed confidently that our answers are correct. Providing screenshots and our own observation strengthens our answers and conclusions. Reference: https://courses.lumenlearning.com/physics/chapter/22-3-magnetic-fields-and-magnetic-field-lines/

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