Part 1. Finding Magnetic North 1. Turn off all the electrical devices at your station because currents in these devices cause magnetic fields! 2. Distribute your compasses on your lab table. You can keep adjusting their locations. They should all point in the same direction, towards Magnetic North. If there are any outliers, disagreeing with the others, set those compasses aside. Describe, relative to the long side of the lab table, in what direction the compasses point. 3. As precisely as you can, measure and record the angle between the edge of your lab bench and Magnetic North. 4. Look at a map of our Campus showing the direction of true north relative to our lab room. Using this information, estimate the difference in degrees between Magnetic North and true North. State the deviation of Magnetic North in degrees East, or West from true North. Record what you have determined and state what you did to make this estimate. 5. NOAA has a magnetic declination calculator: htt s:/ donoaa. ov/ eoma lcalculatorsfma calc.shtml#declination Use this calculator to find the magnetic declination, the number of degrees Earth's magnetic field points East of true north, here in San Jose. Use 95192, our zip code, as the location. Record the magnetic declination from this calculator. How does the value given by NOAA's calculation for the magnetic declination compare to your estimate? (0 Part 2. Magnetic Fields caused by a Long Straight Current 1. Distribute your compasses around the vertical wire running through the center of your platform in an orderly array as depicted in the sketch below. 2. Disconnect all wires from your DC power supply. Turn it on. Turn the current control knob all the way down (full counterclockwise). and the voltage control knob all the way up (full clockWise). In this lab you will be adjusting the current control knob only. 3. Connect the positive and negative outputs of your DC power supply to the OUTSIDE connectors, as shown in the diagram. When you turn up the current. this will send current around the large 50-turn coil. Avertical length of this current Will run right through the center of the circular platform. SO-turn coil wire E I('-' ' n Use \"outside" input I output 4. Slowly start turning up the current control knob to about 1.0-1.5 Amps while watching the behavior of the compasses. Describe your observations. Explain what must be happening to the magnetic field in the region where you placed your compasses. 5. The direction of the magnetic field caused by a long straight wire is determined using the "right hand rule\". Your right fingers curve in a partial-circle around your straight thumb. Line up your curved right fingers with the magnetic field produced by the wires. The red end of the needles on the compasses point in the direction of the magnetic field. Your thumb will point along the bundle of wires in the direction of the current. Is the current flowing upwards. or downwards? 6. Turn down the current control knob to zero. State your prediction for what will happen when you reverse the current direction. 7. Now do the experiment described in (B) by reyersmg the input/output connections. Make sure that you are still using the outside connectors. Slowly turn up the current and watch the compasses. Compare your observations to your prediction. and explain your observations. Part 3. Estimating Earth's Magnetic Field Earthls magnetic field is only parallel to Earth's surface at locations somewhat near the equator. The diagram below shows you the shape and direction of Earth's magnetic field. no, there is no bar magnet stuffed inside the Earth! In the diagram, notice that Earth's magnetic field dips downward into the Earth in the northern hemisphere This downward dip angle of Earth's magnetic eld. measured here in San Jose California is e, : 61 degrees. W. Today we will experimentally determine the component of Earth's magnetic field that is parallel to Earth's surface. called H, . We then find the 'li'J Hr \"IN i/iutrrr.' magnitude of Earth's magnetic field. Him. by using the trigonometric relationship for vectors: : H (305(9) _ ) (Equation 1) [with it.\" mm\": is\To determine the horizontal component of Earth's magnetic field you need to recall a fact about vectors; if two magnetic field vectors are of equal magnitude and perpendicular to each other, the resulting total magnetic field vector will point at an angle of 45 degrees. You will create the situation where ' vector is equal in magnitude to the magnetic field due to the 50 Earth Horizontal long straight wires. And since you know the magnitude to the magnetic field due to the 50 long straight wires = SOB, where B is found using (equation 2), you will have then determined B Earth Horizontal. B"; Ho' zontal component 8,: tom1 l'cid (compass di'oct'on) of Earth fiv d 3. Before turning on the current, position the compass such that the magnetic field of the Earth ( Part '1) is perpendicular to the magnetic field produced by the current in the wire ( Part 2). Make sure that you maintain your measured distance r. Rotate the compass so that the needle aligns itself with 0 degrees. thereby setting Magnetic North to 0 degrees. 4. Slowly turn up the current and watch the compass needle begin to deflect from Magnetic North. Once the needle deflects by 45 degrees, record this current. The magnetic field due to the 50 current carrying wires is now equal to the horizontal component of Earth's magnetic field. Measured Current when the compass needle deflects by 45 degrees. 5. Turn off the current after you have made your final current measurements. \"ti! 6. Calculate and record B ' = 50(B = ,.) below. Show your Mirth Hm Manta! 2TH work. 7. Use (Equation 'i)to calculate B the magnitude of the Earth's magnetic Earth' field here in San Jose. Show your work.