Magnetic Fields and Distance
Clinical engineers design and work with hospital medical equipment.Copyright 2003 Shane T. McCoy, U.S. Navy, Wikimedia Commons https://commons.wikimedia.org/wiki/File%3AUS_Navy_030423-N-6967M-235_Hospital_Corpsman_Wade_Henry_gives_a_passdown_to_the_night_shift_in_the_Intensive_Care_Unit_%28ICU%29_aboard_USNS_Comfort_%28T-AH_20%29.jpg
Students measure the relative intensity of a magnetic field as a function of distance. They place a permanent magnet selected distances from a compass, measure the deflection, and use the gathered data to compute the relative magnetic field strength. Based on their findings, students create mathematical models and use the models to calculate the field strength at the edge of the magnet. They use the periodic table to predict magnetism. Finally, students create posters to communicate the details their findings. This activity guides students to think more deeply about magnetism and the modeling of fields while practicing data collection and analysis. An equations handout and two grading rubrics are provided.
In this activity, students characterize the field strength of a magnet as a function of distance. These types of experiments are done widely by national standards labs, third-party rating agencies, and component manufacturers (such as for magnets). These data are published in graphic and table forms in compilations such as the CRC Handbook of Physics and Chemistry. Then scientists and engineers refer to these publications as they design and determine specifications for parts and equipment.
Clinical engineers, for example, use these data to ensure no medical devices interact with others in such a way that makes erroneous readings or injures patients. Medical devices generate electromagnetic interference (EMI) that can affect the operation of other devices and implants such as cardiac pacemakers. EMI from hospital equipment and other sources such as cell phones, stereo headphones and even toys and jewelry that contain magnets can cause disturbances to pacemakers that currently have low resistance to EMI. Engineers examine magnetic field strength data to reduce patient risk by redesigning devices so they resist higher EMI levels or by designating separate high-EMI areas so people can avoid them—for example, creating “cell-phone zones” for phone use, instead of permitting phone use in patient rooms.
Clinical engineers also use these data to upgrade medical devices such as magnetic resonance imaging (MRI) machines to have lower magnetic field strength so they are safer for people with pacemakers.
After this activity, students should be able to
- Explain how permanent magnets work.
- Explain how a compass works.
- Explain that the magnetic field increases non-linearly as a permanent magnet is brought in from infinity.
- Identify the SI units of a magnetic field, often represented by the variable B and the unit tesla (T).
- Label the axis of a scatter plot with both physical meaning and units.
- Create an accurate scatter plot by hand or using a computing device.
- Manipulate a scatter plot to create a line of best fit, optionally using a computing device.
- Create a model and use it to make a prediction.