# Electricity Theory by LisaB1982

VIEWS: 77 PAGES: 32

• pg 1
```									Electricity Theory
VIR PIV and Capacitors!!!

PEg

Energy


When an object is at some height in a gravitational field it is said to have gravitational potential energy, PEg

Energy


 

Like gravitational fields causing masses to have potential energy, Electric Fields cause charges to have electric potential energy, PEE PEE is a type of mechanical energy MEtotal = KE + PEg + PEs + PEE

Energy




To give something PE you must do work (apply force over a distance) on the something (raising up in g-field) For PEE to occur a FE must be applied by either a. An E-Field (uniform) b. A pair of charges

Energy
Uniform E-field

W  PE  Fd F  Eq PEE  qEd

B
Line Color
Red: E-Field

A

Black: Equipotential lines Blue: charge displacement

Energy


Pair of Charges

W  PE  Fd q1q2 F  kc 2 r q1q2 PEE  kc r

Electric Potential


Any point in an electric field is said to have Electric Potential, V. However, only a Difference V  PE in PE is measurable q (remember zero point) so we talk of electric potential unit  Volt, V difference AKA potential J difference, ΔV. 1V=1

PEE V q

C

Potential Difference

Potential Difference

Potential Difference


Back to the zero point A convenient zero point to chose in a circuit or any electric system is the “ground”

Battery (cells)


A battery produces electricity by transforming chemical energy into electrical energy

Battery
Carbon Electrode

+

Zinc Electrode

Sulfuric Acid

Capacitor




A capacitor is a storehouse of charge and energy that can be reclaimed when needed for a specific application A capacitor will only charge to the potential difference between the terminals of the battery

Capacitance




Capacitance, C: The ability of a conductor to store energy in the form of electrically separated charges Capacitance is the ratio of charge to potential difference

Q C V

unit  Farad, F C 1F=1 V

Capacitance


Capacitance depends on size and shape

A C  0 d
 0  permittivity of free space, 8.85x10
A  Area of one plate d  distance between plates
-12

C 2 Nm

2

Capacitor


Energy stored in a capacitor

1 1 2 U  energy  QV  CV 2 2

Electric Current
 

Movement of electric charge Rate of charge movement

Q I t

unit  Ampere, A C 1A=1 s

Charge Movement

Charge Movement

Circuit Analogy

Types of Current


AC  Alternating current  charges continuously change direction forward and back at 60 Hz


Example: outlets (approx 120 V)



DC  Direct current  charges move in one direction


Example: batteries

AC-DC Debate births the Electric Chair

Resistance




Resistance is the impedance of the motion of charge through a conductor The ratio of potential difference across a conductor to the current it carries

V R I

unit  ohm,  V Js 1  1  1 2 A C

Ohm’s Law

V  IR

Resistance


Depends on: Length, cross sectional area, material, and temperature

L R A

  resistivity, m
L  length, m A  cross sectional area, m2

Resistance and Temp

Resistance and Thickness

Resistor




An electronic element that provides a specified resistance. A current or voltage REGULATOR

Power (it’s Electric!)




Power: Rate at which work is done. OR Rate at which energy is transformed Electric Power: The rate at which charge carriers convert PEE into non-mechanical energy

P  IV

unit  watt, W J 1W=1 s







HW due on test day:
p 599 1-3; p 601 2, 3, 5-9; p 607 1 – 4 (B); p609 1 – 5 p 615 1 – 6; p 616 2-4, 7,9 p 621 1 – 5

pp 593 - 625



Extra Practice
p 626 – 628 11, 20 – 54

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