5/12 (Magnetism,motors,charges)

Lab Day 5/12/15: Magnetism/Motors

Purpose: We will look at how a magnetic field can generate a torque and how this can be used in electric motors.

We began class by looking at an ordinary pin and a magnetized pin. We found that the pin is made up of many bar magnets distributed randomly with one end of the pin south and the other pole north. However, when the pin is magnetized the magnets would align itself so that the north would all be pointing in one direction and south would all be pointing in the other direction.

We found that we can also demagnetize the magnetized pin by heating it and like thor hit it with a hammer and this is shown in the picture.

Rectangular Current Loop

An example was given where we calculated the torque on a rectangular current loop. The equations of force from the previous lesson was derived where we could it apply it to the torque equation which is substituted below to find the net torque symbolically.

Next, the current loop in the magnetic field can generate a torque caused by the forces on its sides. The magnetic dipole moment is derived in the whiteboard below which allowed us to calculate the torque on the loop.

We worked on another problem that involved the torque on a 50 loop coil with a radius 1.00m. The calculations are performed below using the torque equation we found previously.

We can use the right hand rule for torque.

Inside an Electric Motor

We start by looking at a two-pole DC electric motor where it has 6 basic parts. The motor has two magnets. The armature is the electromagnet, and the field magnet is the permanent magnet.

We examined the things that would most likely break in a motor.

The video demonstrates a motor that uses the torque exerted on a current in a magnetic field which allows it to convert into mechanical energy to allow it to spin. In an electric motor, as the half-turn motion is done, the electromagnet flips, which causes the electric motor to spin freely. We developed a motor by using a coil, wire, magnetic metal plates, and batteries.

Saint-Louis style motor that has a wire-wrapped iron core on an axis spindle. The ends are connected to a split-ring commutator.

The Magnetic field near a current-carrying wire

We look at the magnetic field along a straight conductor that carries a current. We apply Oersted's observations to analyze the magnetic field lines that are perpendicular to the wire.

We derived the magnetic field formula using the magnetic dipole moment, the charge q, v, r knowing that Idl is equal to qV.

Superposition of Magnetic Fields

This board shows the superposition of the magnetic field when they are all in the same direction. They would cancel out if they were going in different directions.

Conclusion:
We learned that torque is generated in a current loop in a magnetic field due to forces on the sides. We came up with multiple equations of torque and magnetic dipole moment which allow us to calculate the net torque and rotation using the right hand rule. We were also introduced to motors where we can see that certain electric motors use magnetic fields to rotate the rotor which allows current to run through a wire. Magnetic fields do superimpose (add up) which we also see in electric fields.