Magnetism – Lab 19 Go to http://phet. colorado. edu/simulations/sims. php? sim=Magnets_and_Electromagnets and click on Run Now. Part I: 1. Move the compass slowly along a semicircular path above the bar magnet until you’ve put it on the opposite side of the bar magnet. Describe what happens to the compass needle. The white lead of the needle faces the South part of the magnet in a perpendicular way. When the needle is facing the center of the magnet, the lead turns to a 90 degree angle, being parallel to the magnet.
When the compass faces the North part of the magnet, the needle turns 90 degrees in the same direction until the red lead if facing towards the North of the magnet. 2. What do you suppose the compass needles drawn all over the screen tell you? They represent the magnetic field. 3. How is the strength of the force/torque on the compass needle indicated? By the speed when the direction is changed the faster the needle moves, the greater attraction force. 4. What are the similarities between the compass needle (magnetism) and a test charge (electricity)?
As like electric charges repel and opposite charges attract each other in electricity, like magnetic poles repel and opposite magnetic poles attract. 5. Move the compass along a semicircular path below the bar magnet until you’ve put it on the opposite side of the bar magnet. Describe what happens to the compass needle. The Red lead of the needle faces the South part of the magnet in a perpendicular way. When the needle is facing the center of the magnet, the lead turns to a 90 degree angle, being parallel to the magnet.
When the compass faces the North part of the magnet, the needle turns 90 degrees in the same direction until the White lead if facing towards the North of the magnet. 6. How many complete rotations does the compass needle make when the compass is moved once around the bar magnet? One complete rotation. 7. Click “flip polarity” and repeat the steps above after you’ve let the compass stabilize. The results are the same. 8. Click on the electromagnet tab. Place the compass on the left side of the coil so that the compass center lies along the axis of the coil. (The y-component of the magnetic field is zero along the axis of the coil. 9. Move the compass along a semicircular path above the coil until you’ve put it on the opposite side of the coil. Describe what happens to the compass needle. The Red lead faces the left side of the coil and as the compass is moved towards the upper center part of the coil, the compass is parallel to the coil. As the compass is moved towards the right side, the white lead ends up facing the coil. 10. Move the compass along a semicircular path below the coil until you’ve put it on the opposite side of the coil. Describe what happens to the compass needle. The White lead faces the left side of the coil and as the compass is moved owards the upper center part of the coil, the compass is parallel to the coil. As the compass is moved towards the right side, the Red lead ends up facing the coil. 11. How many complete rotations does the compass needle make when the compass is moved once around the coil? One complete rotation. 12. Use the voltage slider to change the direction of the current and repeat the steps above for the coil after you’ve let the compass stabilize. Same results. 13. Based on your observations, summarize the similarities between the bar magnet and the coil. The Bar magnet and the Coil experiments have the same results.
In both, the compass lead is attracted in one side of the coil or magnet and it rotates 180 degrees by the time it gets to the other side. 14. What happens to the current in the coil when you set the voltage of the battery to zero? The current stops flowing in the coil. 15. What happens to the magnetic field around the coil when you set the voltage of the battery to zero? The magnetic field disappears. The compass lead stops in the direction it was pointing and it does not move even if it is move around the coil. 16. Play with the voltage slider and describe what happens to the current in the coil and the magnetic field around the coil.
As the voltage slider moves to the right, the current flows counter-clockwise going towards the right. The speed of the current increases as the voltage increases. As the voltage slider moves to the left, the current flows clockwise going towards the left. The speed of the current increases as the voltage increases. The magnetic field rotates 180 degrees when the battery slider moves from one side of the battery to the other. 17. What is your guess as to the relationship between the current in the coil and the magnetic field?
The current has a positive charge in one side of the coil and it transforms to negative when it gets to the other side of the coil. This charge controls the magnetic field, making the like charges repeal and the opposite charges attract. Part II – Graphing relationships. Field Strength vs. Position 1. Using the Electromagnet simulation, click on “Show Field Meter. ” 2. Set the battery voltage to 10V where the positive is on the right of the battery. 3. Along the axis of the coil and at the center of each compass needle starting 5 to the left of the coil, record the value of B.
Move one compass needle to the right and record the value of B. Repeat until you’ve completed the table below. NOTE: Be sure to take all of your values along the axis of the coil. You’ll know you’re on the axis because the y component of the magnetic field is zero along the axis. |Compass position (arbitrary |Magnetic Field Strength (fill in | |units) |units) | |-5 |4. 26 G | |-4 |7. 42 G | |-3 |16. 0 G | |-2 |39. 66 G | |-1 |180. 20 G | |0 |300 G | |1 |283. 93 G | |2 |53. 39 G | |3 |18. 37 G | |4 |8. 81 G | |5 |4. 69 G | 4.
What happens to the value of magnetic field strength inside the coil? Stays at 300. 00 G. 5. Graph the compass position on the horizontal axis and magnetic field magnitude on the y axis. Print your graph. Make sure to label the axes and title the graph. [pic] a. Is your graph symmetric? Yes. 6. Using your graph, what is the relationship between magnetic field strength and position? (Use the fit feature of graphical analysis to help you. ) As the compass needle moves closer to the coil, the strength of the field increases. As the compass needle moves away from the coil, the strength of the field decreases.
Part III – Using the simulation to design an experiment. Field Strength vs. Number of Coils 1. Design an experiment to test how field strength varies with the number of coils. |Number of Coils |Magnetic Field Strength | |1 |10. 20 G | |2 |20. 40 G | |3 |30. 60 G | |4 |40. 80 G | 2. Collect data in a table and graph your results. [pic] Field Strength vs. Current 3. Design an experiment to test how field strength varies with the Current. Recall that voltage is directly proportional to current…. Ohm’s Law. ) 4. Collect data in a table and graph your results. |Voltage |Field Strength | |Current | | |0 |0. 0 G | |1 |4. 8 G | |2 |8. 16 G | |3 |12. 24 G | |4 |16. 32 G | |5 |20. 40 G | |6 |24. 48 G | |7 |28. 56 G | |8 |32. 64 G | |9 |36. 72 G | |10 |40. 80 G | [pic]
