Hard Drives
Phenomenon: Hard drives store enormous amounts of information
Student Task:
Construct an explanation based on evidence how magnetic fields and force allow hard drives to store information
Model
Students develop models to visualize and understand invisible magnetic force fields
Investigate
Students plan and carry out investigations to determine the variables that effect the strength of electromagnets.
Obtain Information
Students read to obtain information about properties of magnets and the science behind computer hard drives
Analyze Data
Students analyze and interpret data to determine how to optimize the electromagnetic write head of a computer hard drive
Explanation:
Computer hard drives use the principles of magnetism to store and retrieve information. The hard drive disk is made of an underlying structural material that is not affected by magnetic fields. The top layer of a disk contains iron or cobalt that experiences a force when exposed to a magnetic field. The write head on the actuator arm is an electromagnet composed of wire coiled around an iron core. It produces an alternating north and south magnetic pole pointing toward the disk by continually changing the direction of the electrical current. The magnet on the write head needs to be quite strong so it has many many turns of wire. By using large numbers of wire coils, the current in the wire is kept quite low. Increased current would also produce a strong magnetic field but that would overheat the head. The write head never needs to touch the disk because magnetic field forces act through space with no need for actual contact but the head needs to be extremely close to the disk because magnetic force gets weaker as the distance between the write head and the magnetizable coating on the disk increases. Magnetic force getting weaker with distance also explains why the magnetic spots directly under the read head will be sensed but not the other magnetic spots. Those spots are far enough away that their fields are too weak to be registered by the reader.
The code on the disk is binary meaning there are are 2 numbers 1 and 0. Binary is used because either a north magnetic pole on the spot on the disk is pointing upward or a south is upward. Each spot is called a bit. A collection of these bits together represents a letter in the alphabet, a number, a color and all the other information that is stored on computer hard drives. There are billions of these magnetic spots called bits on today’s personal computers.
Application (Optional STEM Project):
Students apply their knowledge acquired through modeling and investigation to design a model sample section of a computer hard drive. They write a number in binary onto their model that is then read and decoded by another team.
Recommended Teaching Sequence:
Day 1: Introduction to phenomenon and Mapping Magnetic Field Lines models
Day 2: Factors that affect the strength of electromagnets investigations
Day 3: Readings about magnetism and reasoning
Day 4: Designing a model hard drive, reading about hard drives and compose final explanation based on evidence
Formative Assessment:
Use what students have written in their science notebooks as a formative assessment, including
Do students understand that
Lesson Contributor(s):
Charlie Matthews - STEM Endorsement Coordinator Park City School District