Solenoids and Magnetic Fields

Magnetic Fields Inside Current-Carrying Loops

We made some predictions about how the earth's magnetic field changes with respect to angle along three axes. Prof. Mason connected a cylindrical magnetic field sensor to LoggerPro software and projected the results on a screen. Our predictions are in black ink and the actual results.

Magnetic Field Inside a Coil with Varying Loops

We started with a magnetic sensor that was connected to a computer so that we could collect data on LoggerPro.

We then connected a wire to a power source and monitored the current using a multimeter.

Next we coiled the wire around a hollow plastic cylinder. The picture above shows us preparing for our first run, with one loop around the hollow cylinder.

We switched the power source on and measured a current of 1.93 A (the picture shows a different value, in actuality the reading fluctuated a bit).

We carefully held the loop in place with the aid of the hollow cylinder and positioned it to where the sensor on the sensor probe was in line with the wire loop. We collected the data on LoggerPro. After a few seconds of collection, we turned the power off so that we could obtain a "zero" point of reference.

To calculate the magnetic field from our graphs, we used averages. We took the mean of the magnetic field from the time when the power was passing through the wire using the "Statistics" option in LoggerPro. Next we took the mean at a time period when the power was already turned off. We subtracted calculated the difference between the "on" and "off" averages and that became our experimental magnetic field recorded. The graph above shows that we recorded an mean of 0.021 mT when the current was on and 0.007 mT when it was off. So we took the magnetic field to be B_loop = 0.021 mT - 0.007 mT = 0.014 mT. This was our experimental value for 1.93 A and 1 loop.

We repeated the same process as above to calculate the magnetic field. In this trial we have 2 loops, 1.93 A, and 0.023 mT.

This trial shows 3 loops, 1.93 A, 0.027 mT.

Our final trial shows 4 loops, 1.93 A, 0.044 mT.

This table shows the data we collected for all trials. We kept the current constant at 1.93 A for all four trials. In doing so, we can see a direct relationship between the number of loops in the coil to the magnetic field it produces. We can see that as the number in loops increases, so does the magnetic field.

Magnetic Field in Motion

We connected a solenoid which contained many loops to a device that could measure current.

We passed a magnet through the center of the solenoid and observed the meter.

We observed that the reading was affected by the velocity of the magnet. The slower the magnet went, the smaller the reading on the meter.

On the contrary, the faster the magnet was passed through the center the higher the reading. This told us that current was created when passing a magnetic field through the center of looped wires at a velocity. Passing the magnet in the loop quickly caused the meter to go one way and then pulling the magnet back out would cause it to go the other way. When we tried it again with poles reversed, the same thing happened except that the directions were switched from the first orientation.

In this horrible photograph, we can see (or pretend to see) three things that will maximize current output. Firstly, the velocity of the magnet going though will maximize the current flow as observed from our experiments. Second, the strength of the magnet will also increase the current. This can be seen by doubling-up the magnets we were using and passing them through the coils. Lastly, the number of loops in the coil will also increase the current. From our experiment with the magnetic sensor we proved this result.