Force Due to a Magnetic Field, Magnetic Field in a Solenoid, Lenzs’ Law, Faraday’s Law, Magnetic Induction

Force Due to a Magnetic Field

Set Up

In this demo, two wires are placed next to each other and connected to a voltage source. The force due to the magnetic field from wire 2 on wire 1 is solved by the definition of magnetic force current and magnetic field

The current is sent the same direction through the two wires and it was predicted that the wires would move away from each other, however, the wires move towards each other. This can be determined by the right hand rule with the thumb and curl of the fingers. The magnetic field travels in a circle around the wire, but we only care about the part of the magnetic field that hits the other wire tangentially. Using the right hand rule, it can be see that the forces are both pointing towards each other.

Predictions and Answers

When a current is run through each wire in opposite directions, it was predicted to repel each other and it did which was also determined by the right hand rule. 

Magnetic Field in a Solenoid

A magnetic field sensor was used to determine the magnetic field inside of a solenoid.  Wire was wrapped around a test tube and the magnetic field produced by that circle of wire was measured with the field sensor on logger pro.  It can be seen that the magnetic field in a loop is proportional to the number of loops and the current running through the loops. It can be seen that the more loops added, the higher the magnetic field.  Also, the closer together the loops were the bigger the magnetic field was as well. The maximum magnetic field was seen at the end of the solenoid (test tube with wires wrapped around) when the magnetic field was parallel to the area vector.  

Lenzs’ Law

Lenzs law states that a magnetic field always opposes an induced magnetic field and this experiment was to prove that. Two cylindrical objects, one magnetic and one nonmagnetic, are to go through two tubes at the same time.  One of the tubes is made of aluminum and the other is plastic. It was predicted that when the magnetic object is dropped in the aluminum tube it would fall faster because in a conductor, the electric field is equal to zero. However, the magnetic object fell faster in the plastic tube and much slower in the aluminum tube. The magnet induces a current when it moves through the aluminum tube and therefore induces a magnetic field. According to Lenzs' Law, the induced magnetic field points upwards in the opposite direction as the magnetic field and slows the fall of the magnetic object. When the magnetic object is placed in the plastic tube they fall at the same time because the plastic tube isn’t a conductor and therefore no current or magnetic field is induced.

Faraday’s Law

Faradays law states that in order for there to be a flux there must be some change in either the magnetic field, area, or the angle between the magnetic field and area vector is changing.  

Effect of magnetic field changing

smaller area bigger current

This demo was to see if magnetism could create an electric field capable of causing current to flow in a wire.  We tested this by connecting a coil of wire to a galvanometer.  When the magnet was inside the coil of wire, no current was produced.  We determined that the magnetic field must be changing in order to create a current.  We then determined five different ways to maximize the current (see whiteboard for details).

larger area smaller current

Effect of area changing

A large amount of current was applied to the rails of the system shown in the picture of the set up.  When you apply the current to the rod, the rod slides backwards.  What is happening can be explained by one of the right hand rules with the pointer finger, middle finger, and thumb.  When you point your fingers in the direction of the current and magnetic field it can be seen that the magnetic force produced is pushing the rod backwards.  This applies to Faraday's Law because the area of this closed loop is changing while the Magnetic Field being produced by the large magnet at the end of the system and the current flowing through the rod is constant.   

Magnetic Induction

In this demo a current was ran through a coil of wire and when an aluminum ring was placed on the energized coil, the ring began to levitate which means there must be some force acting on the ring.  After taking the ring off the coil it was observed that the ring was warmer than before which is because when the ring was placed on the coil an induced current was flowing through it.  The coil has and original current in it and creates magnetic field going up.  This magnetic field is making an induced current in the ring which is going in opposite direction of the current of the coil.  This current flowing through the ring creates a magnetic field in the ring opposing the magnetic field produced by the coil.  We now have two magnetic fields repelling which is why ring levitates because of interaction between mag field in coil and in ring.

Now we replace the initial ring with another aluminum ring that has a slit in it.  No current can flow through this ring because of the slit which results in a ring that doesn’t get hot which is because there is no current going through it.

A light bulb is attached to a solenoid and put over initial coil that has a current flowing through it and a magnetic field which induces a current and magnetic field in the solenoid above the initial coil and lights bulb.

In an oscilloscope

A function generator was connected to a large coil which was connected to channel 1 of the oscilloscope.  A smaller coil of wire was placed in the large coil and then connected to channel 2 of the oscilloscope.  The image displayed from the large coil is a large sine wave and the image displayed from the smaller coil is the exact same sine wave except for it has a smaller amplitude.  The reason they have the same current flowing through them is because the large coil is educing a current and magnetic field in the smaller coil.  It can be seen when you turn the coil on its side so the holes are now laying horizontally, then the current in the smaller coil is now zero because the magnetic field and the plane of the loop are perpendicular (they must be parallel).  It can also be seen that when you move the smaller coil in the larger coil and move it towards the edge of the larger coil, it can be seen that the current is larger.