5% extra credit

To remind and help teams who takes part in match

Day 22

Changing thumbtack to get magnetic, and use 2 ways to destroy it.

  In this demo, Professor Mason has two coils of wire that can become magnetic when it is connected to a power supply.  A switch is attached to the two coils to change the direction of magnet. When the switch is on, the magnet oscillate. When the magnet is in parallel with magnetic field, the torque is zero. When the switch is on or off, it oscillates and stop. In order to keep the magnet spinning, we need to keep switching it to on and off. 
  2 pole vs. 3 pole
In a two pole motor, it can stop and get stuck but with a 3 pole motor, there is always some torque and that is why most motors are made with an odd number of poles. 

Motor:
Next we build a motor by getting the tool from professor Mason.

After we build the motor, we start to supply power. When power supply is applied, the motor turns one way. When the power supply is reversed, the motor turns another way. 
Forces on a Line of Charge :In this activities, we interpreted the magnetic field by using the right hand rule. When we are doing at the top, nothing happens to the magnetic field because the two currents are canceling out, current going up and current going down. When we go to the area on the right hand side, there are two currents going in the same direction and it gives double the magnetic field. When you go to the area in the middle, there is a magnetic field going through the center of coil. 

Compass and Magnetic Demo:

When a current goes to top, it will make a  magnetic field to around with a center. When the direction of the current is switched, the arrows change directions as well. This demo proves a rod of current has a circle of magnetic field. 

Day21

No class today. No lab today. ☺

Day20

Magnetic Fields:

By using a compass, we can find the direction of a magnetic from a bar magnet, North is attracted to South, and south is attracted to north, too.  Drawing the direction by compass.

 Gauss's  Law in Magnet is defined as ∫B∙dA. ∫B∙dA=0 because there is no monopole, in every single magnet, there will always be south pole and north pole. Thus, the net flux is always zero. 

  Electric Field Lines:
After using compass, we spray some Fe power near a magnet to see the magnetic field. Magnetic fields go from positive to negative. 

Lorentz Force

Lorentz Force Large Magnet Demo

For this lab, Professor Mason shows out a large magnet and set up a copper wire across and in between the magnet.

When we give the current, we found the copper wire jump down, but when we change the direction, the copper wire jump up.

The velocity of the electrons is going through the wire, the direction of the magnetic field is going across the poles of the magnet, and the force is perpendicular to the velocity and magnetic field (Lorentz Force= F=qVxB or F=qvBsinθ).

 Finding Net Force

we find the total force on a wire by using a spreadsheet. (F= IL x B) It can be observed that there is a maximum first at 90 degrees and a minimum on the sides. 

Day19

 Analog and Digital Electronics:

For this lab, we connect our phone to with the oscilloscope and a speaker, and we download the tone generator app to help to find the highest frequency that a phone can put out through the music.

 When we played two songs, the wave we see:

In the this lab, we built the LED light circuit on the circuit board. When the power supply is on, the LED light is on. But some we find the LED light is off because LED light is a diode, when we put the power supply backward, the LED light will remain off. 

Low Pass filter:
For the low pass filter lab, a circuit is set up by using a 0.1 uF capacitor, a 22K resistor, 2.2Meg, 3.3K resistor, and 0.22uF capacitor. The circuit was connected to the oscilloscope and with the tone generator app. we could find that resistors are not frequency dependents and capacitors are. 

Day18

Oscilloscope and Mystery Box:

In this class time, AC/DC and other components of the oscilloscope were studied, and more and more familiar of  the oscilloscope is learned for future labs. All observations are made on the whiteboard photos below.

Mystery box:

After knowing the property of AC and DC and other components of the oscilloscope, we are going to measure a mystery box. This is how a mystery box looks like.

 Using the oscilloscope, we can find the frequency, time and voltage. 
                                   The value makes sense.  

Day17

Capacitors in Series and Parallel

1. A Capacitance Puzzle:
Predict: When the Capacitor connected in parallel. The capacitance equals to the sum of the each capacitance.
Experiment set up:

2. Quantitative measurements on an RC system.

Predict: When the battery is removed or turn off from the circuit, the voltage across the capacitor will stay same, because the charged battery will lose the potential energy across the resistor, but the circuit is an open circuit, the potential energy does not lose. Since, it is stay st same.
Experiment set up:

In the experiment, our predict is acceptable. But during the measuring, we found it is not perfect march because some of  potential energy from the capacitor is restored by wire.

Activities: Calculation of unknown capacitor:

 With the equation Ae^(-ct) + B，a best fit line is made for each of the graphs. The relationship between potential/voltage and time for a charged capacitor can be conclused VC=Vmax (1-e*(-t/RC)) and for a discharged capacitor it is VD=Vmaxe^(-t/RC). In our lab, the initial voltage is not correct because we do not start from 0. So when LoggerPro tries to do best fit line, it does not start at the right time.