May 12 2015

We list some method to destroy a magnet. 

We draw the force diagram for a loop in a magnetic field, and we also find its net torque. We derive a formula for the net torque of a loop, and it is related to current, area vector and magnetic field. Also, it is a cross product.

We list some method to increase the magnetic force for a loop. Instead of increase current and magnetic field, we can increase the number of loops.

We are given a small electromotor. By changing current and position of pole(changing direction of magnetic field), we observe the change of motion, such as spin direction and the speed it spins.

We also make our own electromotor. If we increase the voltage, it will spin faster. later we use another loop which has more number of loops, and it also spins faster.

This lab shows us that current can produce magnetic field. It is intially turned off, after we turned it on, the campass will spin.

This is our prediction that we make for the direction those campass pointing to after we turned it on.

After we turned it on, the direction for the campass pointing to forms a circle, which doesnt match our prediction.

At this time, we use small campass to detect the magnetic field at some positions around a circuit. We have a conclusion that for a wire, we can add magnetic up to get total magnetic. Different direction of current will cause opposite magnetic, that is the reason we have 0 magnetic field at some point.

For a wire, we are introduced a new formula for calculate the change of magnetic field based on length vector, current and position vector. Again, it is a cross product, thus we have to do it in 3D

Summarize: Wire that has current through in it will be applied magnetic force if it is in a magnetic field. Based on this truth, we develop electromotor. Also, electric can cause magnetic field which has been proved by the spining of campass when we make the wire has current.