Model 2.2 - 2.3 Electrostatics and Electrodynamics

Electrostatics

Study of electric charges in stationary form

Charge is measured in

coulombs

Friction

transfer of e^- by rubbing objects together

Contact (conductions)

transfer of e^- by touching an electrified object to another object

Induction

Charged and uncharged objects DO NOT touch

What charges are imparted when electrification by CONTACT occurs?

imparted with the same charge

What charges are imparted when electrification by INDUCTION occurs?

imparted with the opposite charge

List the Law of Electrostatics

1.      Like charges repel, unlike charges attract

2.      Coulomb’s Law (electrostatics law)

1.      Distribution of charge

1.      Concentration of charge

Coulomb’s Law (electrostatics law) - The forces between two charges is:

1. Directly proportional to the magnitude of the 2 charges

2. Inversely proportional to the square of the distance

Distribution of charge

Over outer surface only of a dense conductor or a hollow object

Concentration of charge

Concentrated at sharpest curves on irregular objects

Strong fields =

more lines of force

Strong field =

closer lines of force

Electrodynamic

study of electric charges in motion

Conductor:

Allows electrons to flow

Insulator:

Inhibits the flow of electrons

Other names for Insulator

Nonconductor and dielectric

Semiconductor:

Acts as both a conductor and an insulator

Superconductor:

Allows electrons to flow without resistance

Components of a Circuit

1.      Current (amperage) (I = Intensity)

2.      Potential Difference (V = Voltage)

3.      Resistance (ohms) (R = Resistance)

Current (amperage) =

I = Intensity

Potential Difference =

V = Voltage

Resistance (ohms) =

R = Resistance

Unit of Current:

rate of electrons flowing per second

ampere =

Charge/time

Potential Difference:

force that causes charges to move

Other names for Potential Difference:

Electromotive Force; EMF; voltage

If potentials are connected by a conducting path e^- will flow from

high - to low – (negative to positive)

How come the battery isn’t connected from the inside?

There’s an insulator inside the battery

Meters are

Devices to determine electrical values

Voltmeter:

Measures PD (Potential difference)

Voltmeter are :

Connected across load (parallel connection)

Ammeter:

Measures current (intensity, ampage)

Ammeter are :

Connected in path so all e^- pass through it (series connection)

Which meter is connected via series connection?

Ammeter

Which meter is connected in a parallel connection?

Voltmeter

Which meter measures potential difference?

Voltmeter

Which meter measures current?

Ammeter

Resistance

Anything that opposes or limits current

The Amount of R dependent on

1. Material

2. Length of Path:

3. Cross sectional area:

4. Temperature:

Length of Path vs Resistance

Direct relationship

Cross sectional area vs Resistance

Inverse relationship

Temperature vs Resistance

Direct relationship

What are the following that increases resistance?

longer length, smaller cross section, and higher temperature

As the length of the conductor increases, what happens to the resistance?

resistance increases

Ohm’s Law

Voltage in a circuit will be equal to the current times the resistance

Ohm’s Law Formula

V = I x R

I = V/R 

R = V/I 

Electric Power Formula

P(power) = V x I

Electric Power Unit

Watts, W = J/s → KW (kilowatts = 1000)

Formula for Finding Power using I & R

P = I² R

Direct Current (DC)

a.     Steady direct current

b.     Pulse Direct Current

Steady direct current:

DR will flow and stay steady at a certain level it tops off and then, once it’s turned off, it goes down (the current)

Pulse Direct Current:

You turn it up, it’ll flow up to the peak, drop down, flow up to peak, and continue this pattern.

Alternating Current (AC)

e^- flow one way then the opposite way

Capacitor

Uses electricity and metal plates to create Potential Difference

Capacitor is

• Another source of potential difference

• A device that temporarily stores in an electric circuit

Capacitance

Ratio of charge stored to potential difference between plates

Resistor

Battery

Capacitor

Ammeter

Voltmeter

Switch

Transformer

Rheostat

Diode

A circuit has 90 volts of EMF and 30 amps. What is the resistance? What is the power loss?

R = V/I → 90/30 = 3 ohms

P = (I)²R → (30) ²(3) = 2700 watts or 2.7 kW

A circuit has a current of 10 amps with 34 ohms of resistance. What is the voltage? What is the power loss?

V = (I)(R) → (10)(34) = 340 V

P = (I)²R → (10) ²(36) = 3400 watts or 3.4 kW

A circuit has 120 volts and 26 ohms of resistance. What is the amperage? What is the power used?

I = V/R → 120/26 = 4.61 amps

P = (I)²R → (4.61) ²(26) = 552 watts

Battery uses

chemicals to create a potential difference!

A 15A fuse is placed in a 110V power line.  What is the maximum amount of power the line can carry before the fuse will activate?

R = 110/15      →     R = 7.33 ohms

P = I²R = (15)² (7.33) = 1649.25 W

Find the power of a 240W  light bulb that draws a 0.46A current.

P = I² R = [0.46A]² 240 W = 50.784 W  →   51 W

A 15A fuse is placed in a 110V power line.  What is the maximum amount of power the line can carry before the fuse will activate?

P = I x V  → 15A x 110V= 1650W =  1.65 kW

Examples of Conductor

metal and water

Examples of Insulator

Rubber