May 08, 2014 · Count Alessandro Volta. 3Current Electricity.notebook 5 May 08, 2014 Dutch & Germans 1744 Before batteries, electricity was hardly worth it

3Current Electricity.notebook

1

May 08, 2014

Current Electricity

Why does water flow downhill?


2

May 08, 2014


3

May 08, 2014


4

May 08, 2014

Khujut Rabu

National Museum of Iraq

1936

Wilhelm Konig

(about $7)

1798

17451827

Where did we get the battery?

Voltaic Pile

Count Alessandro Volta


5

May 08, 2014

Dutch & Germans

1744

Before batteries, electricity was hardly worth it.


6

May 08, 2014

1Acid will attack the zinc, and

dissolve it; zinc ion enters the solution, leaving behind two electrons.

2Electrolyte momentarily becomes positively

charged.

3Electrons are pulled off of the

carbon electrode.

A battery can sustain a voltage across its terminals independently through the use of chemistry.

Chemistry to the rescue!


7

May 08, 2014

Cathode vs Anode Confusion

From your Chemistry class: Anode

+ Cathode

Most physics books (who dare):

dictonary.com

wiktionary.org


8

May 08, 2014

Conventional Currentidea that positive charges flow

(Ben Franklin)

Electron Flowidea that negative charges flow

(modern)

Direct Currentcharges only flow in one direction

charges never turn around

Alternating CurrentCharges vibrate and are not actually displaced

V V

t

t


9

May 08, 2014

http://www.energizer.com/learningcenter/pages/howbatterieswork.aspx

Significance of a battery:it is a self sustaining voltage source

The modern battery is a beautiful thing!

http://www.energizer.com/learning-center/pages/how-batteries-work.aspx


10

May 08, 2014

Closed Circuitunbroken

conducting path from anode to

cathode


11

May 08, 2014

Georg Simon Ohm 1789 – 1854) German

Resistancesignificant restriction on charge flow

Ohm's LawV = I R


12

May 08, 2014

Currentrate of flow of charge

AndréMarie Ampère 1775 – 1836French


13

May 08, 2014


14

May 08, 2014

2. A CD ROM drive in a laptop computer uses a current of 0.27 A in one minute. How many electrons pass through the device?


15

May 08, 2014


16

May 08, 2014

3. A toaster has a resistance of 14 Ω and is plugged into a 120-V outlet. What is the current in the toaster?


17

May 08, 2014

6. A battery charger is connected to a dead battery and delivers a current of 6.0 A for 5.0 hours, keeping the voltage across the battery terminals at 12V in the process. How much energy is delivered to the battery?


18

May 08, 2014

8. The resistance of a bagel toaster is 14Ω. To prepare a bagel, the toaster is operated for one minute from a 120-V outlet. How much energy is delivered to the toaster?


19

May 08, 2014

Electromotive Forcevoltage across the terminals of a battery when it is NOT connected

to a circuit

Terminal Voltagetrue, actual voltage of a batteryespecially when it is connected

in a circuit

Terminal Electromotive Internal VoltageVoltage Force Losses=

V = - i r


20

May 08, 2014


21

May 08, 2014


22

May 08, 2014


23

May 08, 2014


24

May 08, 2014

Resistance and Resistivity

R = ρ LA

(on formula sheet)


25

May 08, 2014


26

May 08, 2014

11. A coil of wire has resistance of 38.0 Ω at 25 and 43.7 Ω at 55 . What is the temperature coefficient of resistivity?


27

May 08, 2014

Electric Power

(on formula sheet)


28

May 08, 2014

Electric PowerSubstituting V = IR into P = IV:


29

May 08, 2014


30

May 08, 2014


31

May 08, 2014

Series Wiring Series wiring means that the devices are connected in such a waythat there is the same electric current through each device.


32

May 08, 2014


33

May 08, 2014


34

May 08, 2014

Parallel wiring means that the devices are connected in such a way that the same voltage is applied across each device.

Parallel Wiring


35

May 08, 2014

The two parallel pipe sections are equivalent to a single pipe of thesame length and same total cross sectional area.


36

May 08, 2014


37

May 08, 2014

Basic Circuit Analysis (Packet Pg 1)


38

May 08, 2014


39

May 08, 2014


40

May 08, 2014

Packet Pg 13


41

May 08, 2014

Gustav Kirchhoff18241887German

What if the circuits are more complicated?

I have ways to make stubborn circuits behave!


42

May 08, 2014

Kirchhoff's Loop Theorem(aka Conservation of Energy)

Ʃ V = 0The sum of all the voltages around a closed loop is zero.


43

May 08, 2014

Kirchhoff's JunctionTheorem(aka Conservation of Charge)

What flows into a junction must flow out of the junction.


44

May 08, 2014

Packet Pg 13


45

May 08, 2014

Signs on Voltages with Kirchhoff's Loop Rule

Battery Resistor


46

May 08, 2014


47

May 08, 2014


48

May 08, 2014

Packet Pg 20


49

May 08, 2014

Capacitors in a Circuit

V = 20.0 VoltsC = 8.00 mF

After the circuit comes to a steady state, how much charge is stored on the capacitor?

Steady StateCapacitor(s) are "full"

ΔV across capacitor(s) balances ΔV across battery

Hint: Q = CV

Q = (8.00x103 C/V) (20.0 V) Q = 0.160 C


50

May 08, 2014

Capacitors in ParallelV = 20.0 VoltsC1 = 8.00 mFC2 = 10.0 mF

After the circuit comes to a steady state, how much charge is stored on each capacitor?

Hint: Q = CV

Q1 = 0.160 CQ2 = 0.200 C


51

May 08, 2014


Q1 = 0.160 CQ2 = 0.200 C

Notice something: Q1 + Q2 = 0.360 C

which is the same as (C1 + C2) V (18.0x103)(20.0) = 0.360C

Equivalent Capacitance of Capacitors in ParallelCp = C1 + C2 + C3 + ...

(on formula sheet)


52

May 08, 2014


After the circuit comes to a steady state, how much charge is stored on each capacitor?

Hint: Q = CV

Q1 = 0.160 CQ2 = 0.200 C


53

May 08, 2014


Q1 = 0.160 CQ2 = 0.200 C

Notice something: Q1 + Q2 = 0.360 C

which is the same as (C1 + C2) V (18.0x103)(20.0) = 0.360C

Equivalent Capacitance of Capacitors in ParallelCp = C1 + C2 + C3 + ...

(on formula sheet)


54

May 08, 2014


55

May 08, 2014

Capacitors in Series

...

All capacitors in series, regardless of their capacitances, contain charges of the same magnitude, +q and q, on their plates.


56

May 08, 2014


57

May 08, 2014


58

May 08, 2014

Resistor Capacitor Circuits

Capacitor Charging:


59

May 08, 2014


60

May 08, 2014


61

May 08, 2014


62

May 08, 2014


63

May 08, 2014

Capacitor Discharging:


64

May 08, 2014


65

May 08, 2014


66

May 08, 2014


67

May 08, 2014


68

May 08, 2014


69

May 08, 2014


70

May 08, 2014


71

May 08, 2014


72

May 08, 2014


73

May 08, 2014


74

May 08, 2014


75

May 08, 2014


76

May 08, 2014

Documents

May 08, 2014 · Count Alessandro Volta. 3Current Electricity.notebook 5 May 08, 2014 Dutch & Germans 1744 Before batteries, electricity was hardly worth it