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Where IS North?

In this experiment, you will measure the magnetic field of the Earth. You will use this data to determine magnetic north. Knowing the direction of true north, you will calculate the magnetic declination at your location.

Created By

Adapted from Experiment 3, Earth Science with Vernier, © Vernier Software & Technology

Programming Language

Any language supported by Hummingbird

Subjects

Science

Grades

6-8, 9-12

Objective & Learning Goals

In this experiment, you will

  • Build a robot to rotate a magnetic field sensor 360°.
  • Write a program to record angles and magnetic field strength.
  • Use a magnetic field sensor to measure the magnetic field of the Earth.

Overview

Where IS north? It depends. Do you mean geographic north or magnetic north? The geographic (true) north pole is the point at 90° N latitude. It is aligned with the rotational axis of the Earth. The Earth is surrounded by a magnetic field with a north and south magnetic pole. The magnetic north pole is the point to which a compass needle points. It is currently in northern Canada, but moves at an average rate of 15 km per year due to complex fluid motion in the outer core of Earth. Depending on your location, the difference between magnetic north and geographic north, called magnetic declination, can range from 0° to 30°.

In this experiment, you will measure the magnetic field of the Earth. You will use this data to determine magnetic north. Knowing the direction of true north, you will calculate the magnetic declination at your location.

Materials

  • computer with Birdbrain Robot Server and Scratch
  • Hummingbird board
  • Vernier BTA sensor adapter for Hummingbird
  • Vernier Magnetic Field Sensor
  • glue gun
  • cardboard
  • rubber bands

Procedure

  1. Bend the magnetic field sensor so that the end is at a right angle to the handle of the sensor.
  2. Connect the Vernier BTA sensor adapter to the Hummingbird. Then connect the magnetic field sensor to the adapter. Set the switch on the magnetic field sensor to 0.3 mT (high amplification).
  3. You need to build a robot that will rotate the magnetic field sensor to a variety of angles between 0° and 360°. To do this, you should use two servo motors. One possible design is shown below. The top servo rotates from 0° to 180° while the bottom servo is at 0°. Then the bottom servo moves to 180°, and the top servo rotates from 0° to 180° again. In this way, the top plate can stop at any angle from 0° to 360°. There are other possible designs! Note: If you mount one servo on top of another, make sure that the axes of rotation of the two servos lie along the same line.
  4. Once you have a robot that can stop at angles from 0° to 360°, mount the magnetic field sensor on it in the orientation shown below. DO NOT use hot glue on the magnetic field sensor! You can use rubber bands to gently attach it to your robot.
  5. To read a measurement from the magnetic field sensor, you will use the HB voltage block. This block will read a voltage between 0 and 5 V.
  6. The Vernier manual for the magnetic sensor provides a linear equation that you can use to convert voltage to magnetic field strength (in millitesla): magnetic field = (0.16 mT/V)*voltage – 0.32 mT
  7. In this experiment, you need to record a number of magnetic field measurements. You should write a program that saves these measurements in a list. Your program should meet the following requirements:
    1. The magnetic field sensor should stop every 15° between 0° and 360°.
    2. At each stop, the program should record the angle in one list and the magnetic field sensor reading in another list.
    3. The program should graph the magnetic field measurements to the screen. The measurements should be scaled so that this graph occupies most of the screen.
  8. Look at your graph. Where is the magnetic field highest? This is the direction of magnetic north! Look through your lists to find the angle with the highest magnetic field. Be sure to record this value.

Processing the Data

  1. Consult a map to estimate the direction of north for your location. How does this compare to the direction you identified in this experiment? If a compass is available, use this to measure the direction of magnetic north and compare it to your results.
  2. The difference between the measured magnetic north and true north is called magnetic declination. What is the magnetic declination for your location? What modifications would be needed on a compass in your location to keep you on course when following a map?

Extensions

  1. Modify your program so that it automatically calculates the angle of magnetic north. Then make the robot point the magnetic field sensor in this direction. Use LEDs to show the user the direction of magnetic north.
  2. Research current theories on why the magnetic north pole moves.
  3. Scientists have found that the magnetic field of the Earth is continually changing. What would be the implications of a big change?