DAY 3 3/1 Series and paralle

Cook hotdog

At the beginnging of the class,professor showed us a hotdog and apply 120V potential arcoss it. Then we do the prediction.

In this photo, we draw  a graph of current vs. Time through the hotdog. And we guess that the hotdog will slowly cook because the resistance of the hotdog is very small.The potential energy transferred to the hot dog and slowly cook it.

In this video, it shows that my prediction is correct. The hotdog is slowly cooking. then the smog come out. 

In this photo,professor insert LEDs into the hotdog both parallel and perpendicular to the hotdog axis. We need to predict that which Led will light.

In this photo,we predict that The LEDS which parallel to the hotdog will light due to the V difference.

Explanation:When we add voltage  to the hot dog, there is potential difference at the hot dog .When we put the LED light horizontally,there is not potential difference across the LED light. Therefore, LED light lights when paralle to the hotdog.

Dependent source example

In this two photos, they are examples of dependent source. we use Kcl circle to find the v and i.

SERIES RESISTORS AND VOLTAGE DIVISION 

In this photo, the resistors are series, and the source of V is Vin and the Vout between R1 and R2. we find the equation of I=Vin/(R1+R2) and Vout= Vin*R2/(R1+R2)

In this photo, the Vin=12V, Vout=3.3V, we find that R1=870ohms, R2=330ohms.

These two photos are also example about series of resitants.

PARALLEL RESISTORS AND CURRENT DIVISION 

The equivalent resistance of two parallel resistors is equal to the product
of their resistances divided by their sum.
The equivalent conductance of resistors connected in parallel is the sum
of their individual conductances.

In this photo, it is an example about series and parallerl resistant, and we find that he Rtotal=R.

Experiment:Dusk-to-Dawn Light
Purpose: to build a circuit that is light sensitive by using bipolar junction transistor as a current controlled current source and photocell which is responded to the light intensity applied to the sensor
Pre-lab question.

In this photo, we find when R is 5 kohms the Vb=1.67V, when R=20kohms, the Vb=3.33V

Experiment set up:

In this photo, we connect all the equipment.

In this photo, we measure the voltage of the BJT(Vb) and the voltage difference across the diode(Vd).

In this photo, we meause that when the light is off, the Vb=0.61V, Bd=0.21V, when the light is on, Vb=2.52v, Vd=1.23V. 

Video of this experiment.

Summary:
Today, in the class, we learn about dependent source example,series resistors,parallel resistors and voltage division. Then we did the experiment: Dusk-to-Dawn light and knew what is BJT and how it works. Then we learn about potentionmeters and DC meters.