Hands-on Science!
         The demonstration I prepared for this lesson was very easy to make, but brilliant in showing the electromagnetic effects and how a hard drive works. I will explain how the model was made after, but I will first show how each part works and what they represent in a hard drive.

Picture of the main part of the demonstration. The 4 magnets represent 4 bits.

         Let us first start off with the core component of the demonstration pictured above. Four magnets are connected to the plexiglass stand which represent the 4 bits of data. They are attached by screws in such a way that the magnets are allowed to rotate freely, with a little bit of added friction from a foam padding. Attached on the magnets is red or black tape: red tape to signify the north pole of the magnet, and black tape to signify the south pole. This is slightly different from how real hard drives use ferromagnetic specks as noted before, but it works the same way. When acted on by an outside magnetic source from the top, the magnets will align properly and store the bit of information to be read after or written over when needed.

A close up picture of the magnet. The red and black tape shows the magnets alignment.

        One other part of the demonstration is the write head of the hard drive. A solenoid is attached to an h-bridge switch which is controlled by the demonstrator. What a solenoid really is will be discussed later, but for now, all that is needed to be known is that the direction of the current running through the solenoid dictates whether it produces a north magnetic field or south magnetic field at the top and the opposite field on the other. This is nearly identical to the write head inside hard drives that align the ferromagnetic specks in the desired polarity. The h-bridge is something that allows for easy switching of the direction of the current, and the 4 9V batteries are needed to produce a strong enough magnetic field so that it can flip the magnets from a good distance away.

A model of the write head, the "h-bridge" switch is shown on the right. The 4 9V batteries are connected in series.

         The last component of the demonstration is the read head. As a hard drive does not have eyes, it needs a way to determine what the magnetic field orientation is. Although a real hard drive does this though the GMR effect, the model uses Faraday's Law of Induction (which will be explained later) to produce a positive or negative voltage through a solenoid depending on the orientation of the magnetic field. The solenoid is connected to an anmeter so that we can physically see the direction of the current, while if it was linked to a computer, it would receive it as is and process it as 1's or 0's.

The anmeter and solenoid. The solenoid is connected in such a way that if it is brought towards the magnet from the top, a positive current will be induced by a north polarity and negative by a south polarity.

         As for the recreation of the demonstration, the materials are:

-four magnets
-screws and nuts
-a decently large sheet of plexiglass and a heat gun to bend it as needed
-foam (optional)
-either colored tape or glue and arrows
-two solenoids
-an anmeter
-a h-bridge of sorts (optional)
-wire and soldering materials

         The magnets should be chosen based on if they have a hole in them, its ability to balance (bar magnets for example, are too hard to balance if used in this way), and its strength. The screws should be able to fit through the hole in the magnet. The plexiglass size is variable, but its minimal size has to be so that it can place the four magnets far enough apart so that they do not affect each other. The stronger the magnet, the further they must be placed away from each other. The h-bridge is also optional as it is only for convenience and not function, as alligator clips can be used to also easily switch the direction of the current manually.

         First, cut a piece of plexiglass to the desired dimensions, and then drill holes just big enough for the screws to fit through. After that, use the heat gun to bend the bottom to form a stand by cutting a slit down the middle and bending the two sides in opposite directions. Slot the magnets in to the screws with a little square piece of foam behind the magnet, and firmly secure the screw with nuts on both sides of the plexiglass. This set up should allow the magnets to freely rotate, and will not losen the nuts securing the screw in place. After that, add arrows as necessary, but leave one blank if you want to show that the arrows are not necessary to determine the magnet's orientation.

         For the read and the write head, you can choose to use alligator clips to clip everything together, but this will produce a rather flimsy demonstration that could fall apart at times. Think about which way each thing should be connected and test it first before soldering anything together. Search up here how to make a h-bridge for the write head. To ensure a strong magnetic field is produced, acquire solenoids that have an iron core within them, or a solenoid with many many coils so that you do not need many batteries, which could be potentially hazardous.