Day 1. 2/23 Current, voltage , power and energy

At the beginning of the class, we first review some questions in physics 4B

In this photo, the circuit photographed below includes three identical light bulbs and two identical batteries, wired as seen in the photograph. In this photograph the switch is OFF, that is, the circuit is open at that point. The intensity level of the two light bulbs is identical (well, almost in the photograph).  And we need to find the change of three light bulbs.

In this photo, we draw the grap and ananly the change of three bulbs. At first, we think that the middle one will turn on, the upper one will dimmer and the lower one will keep same. But when the professor told us the answer, we are totally wrong. The right answer should be the middle one is still off because the voltage between it is 0, and the upper and lower one keep same because the voltage difference is still V, so there is no change on them.After doing this, i know that i almost forgot all things I learn in physics 4B class. But for engineering 44 class, we still use it, so i deceide to review what i learnt in physics 4B class one year ago. 

In this photo, we did an example,the charge transferred in time is given as shown where the peak value is 10 C and the time at the maxima is 0.785s.  Determine the current, I(t), flowing through the wire. According to this graph, we know that the Q=10sin(wt),so I=10wcos(wt). And we also know the 1/4T is 0.785, so the T=3.14s. Then the w=2pi/T=2, so we can find that I(T)=20COS(2t).

Then we need to determine the total charge flowing through an element for 0 < t < 2  seconds when the current entering its positive terminal is I=e^(-2t). and we find that Q=1/2(1-e^(-4)).

In this photo, we did another exercise about current,power and energy.Given v = 10V and i(t) as shown below, sketch the power and energy as a function of time.

We draw the graph of power and energy in the photo. 

After break, we did the first experiment of this class. The name is Solderless Breadboards, Open-circuits and Short-circuits. 
Solderless breadboards, Open- circuits and Short-circuits
Purpose: the purpose of the lab is to provide users with an introduction to some of the equipment such as breadboards and digital multimeters  (DMMs), and determine connections correspond to open circuits and short circuits. we use jumper wires, breadboards and multimeter as an ohmmeter to set up the experiment.

 We use different holes in breadboard to measure the resistant. we should use breadboards, DMMS.The purpose of this lab assignment is to provide users with an introduction to some of the equipment which will be used in subsequent lab assignments. 

In this photo, it is  the situation No.1
we use  DMM as an ohmmeter, connect the leads of the DMM to two holes in the same row on = breadboard, as shown in this photo.

In this photo, it is situation No.2
we check the resistance between two rows of
holes on opposite sides of the central channel of the breadboard, as shown.

In this photo, it is situation No.3
We check the resistance between two arbitrary holes (not in the same row) of breadboard

Situation No.4,we use a jumper wire to connect two different rows on the breadboard. Add a jumper wire between nodes a and c as shown.

In this photo, we record all the data we meausre for the 4 situations. 
1.we record the 2.3 ohms, The DMM indicate a very low resistance between the holes,it's a short circuit.
2.we record the 1 ohms,The DMM indicate an infinite resistance between the holes.it's a open circuit.
3.we record the 1 ohms,THe DMM indicate an infinite resistance.it's a open circuit.
4.we record the 2.3 ohms,The DMM indicate the resistance between these nodes is now very low.
for situation 1 and 4 are closed circuit. situation 2 and 3 are short circuits.it's a short circuit.

Then professor let us draw the breadboard and connect all the holes. 

When the DMM indicates a very low resistance between the holes, it represents a short circuit because a short circuit is caused by a very low resistance in the circuit such as connecting two wires and situation in No.2 and No. 3.  When the DMM indicates to infinity between holes, it represents an open circuit because an open circuit is cause by disconnected of the wire. The resistance of the air is infinity.

Next, we did an exercise.
in this photo,the figure shows the current through and voltage across a device.  Find the total energy absorbed by the device for the period 0 < t < 4 seconds.  
Accoring to the graph of current and voltage, we draw the graph of power at the left and the graph of energy at the right.

In this photo, we calculate the total energy in 4 seconds that the total energy is 0.916J.

At the end of the class, we had an example for power. Given the circuit , find V0. 

we know that conservation of energy and the sum of the power in all the elements is 0.  So we can know the V0=20V.

Summy:
At today's class, we first review what we learn in physics 4B class, including current, voltage, power, energy. we did different exercises about them.And we did the experiment by using breadboard and DMMS to measure the resistant. We also learn that the dependent and independent sources