Kirchoff's Laws

We started off class by reviewing Kirchoff's Current Law and Voltage Law in series and parallel circuits.

Kirchoff's Current Law

• The current is conserved in a series circuit. It is the same throughout the circuit. I1=I2=I3=IT.


• The total current in a parallel circuit is the sum of the current through each resistor connected in parallel. I1+I2+I3=IT

Kirchoffs Voltage Law

• In a series circuit, th total (Vt) is the sum of the potential difference across each individual resistor connected in series. V1+V2+V3=VT


• In a parallel circuit, the voltage is conserved. The potential drop across each resistor in a parallel is equal to the total voltage. V1=V2=V3=VT

Then we did book questions Page 646#1-4

After that we looked at Electrical Rsistance. Electrical resistance is the amount of current drawn from an electrical energy source depends on the internal resistance of the appliance that is "plugged in" and where R=P(L/A)

R=resistance

P=resistivity

L=length

A=cross-sectional Area

We also looked over Ohm's Law V=IR

• If the voltage is constant , an increase in curent(I) must be the result of a decrease of resistance


• If the resistance is constant, an increase in voltage results in a directly proportional increase in current.

Resistors in Series

The total restistance is equal to the sum of individual resistor on series

Rs=R1+R2+R3+..+Rn

Resistors in Parallel

The total resistance is a reciprocal relatonship.

1/Rp=1/R1+1/R2+...+1/Rn

As more resistors are added, the total resistance becomes less. Therefore, the total current will increase

Current and Electric Potential Energy

We started off the class with current. Current is the flow of charges through a wire similar to water flowing through a hose.



There are two different conventions for current:



1) Coventional Current- electric current originates from the positive terminal and goes to the negative terminal. This is a flow of positive charges.



2) Electron Flow Current- current goes from the negative to the positive terminal and represents a flow of electrons.



The Formula for Current is I=Q/t I=current(amps) Q=charge(coulombs) t=time(seconds)



There are two types of current that exist. The AC or alternating current is when the charges in the current change direction. The DC or direct current is when all the charges in the current travel in one direction.



Ex:Calculate the amount of current flowing through an electri toaster if 900C of charge is used to toast 2 slices of break in 1.5 minutes.



Q=900C, t=1.5min.-90.s I=? I=Q/t---> 900C/90.s=10A



Next we talked about Electric Potential Energy. This concept states that if a negative charge were to be placed between a negatively charged plate and a positively charged plate, the negative charge would be attracted to the positively charged plate. Therefore there would be the maximum electric potential energy between the negative charge and the positively charged plate, and no electric potention energy between the negative charge and the negatively charged plate.

The work done per unit of charge is called the electric potential different and it is equivalent to voltage.The formula is: V=W/Q

V=potential difference(volts)W=work(J)Q=charg(C)

Lastly we learned that an electric potential difference must exist in order for current to flow in an electric circuit.