Prime Movers

1
Prime Movers

• Electrical Systems

2
Atomic Theory

• Atoms are made up of
• Protons ( charged)
• Neutrons (neutral no charge)
• Electrons (- charged)
• Principle of conservation of charge
• 3 ways to charge an object
• Friction (rubbing off electrons)
• Conduction (transferring by contact)
• Induction (placing it near a charge, polarizing)

3
Conductors vs. Insulators
Charges can only move through conductors. Some
metals are better conductors than others because
their electrons are more loosely bound (thus more
free to move). Insulators do not allow free
movement of charge.
This side has some conductance, but not as much
as the opposite end.
This end has more conductance
4
Static Electricity

• Charge can be collected or built up on
  insulators
• Charge can be removed by grounding
• Like charges repel and opposites attract

5
Charging an Object
6
Static Electricity

• When we rub two different materials together,
  which becomes positively charged and which
  becomes negative? Scientists have ranked
  materials in order of their ability to hold or
  give up electrons. A list of some common
  materials is shown here. If two materials are
  rubbed together, the one higher on the list
  should give up electrons and become positively
  charged.
• your handglassyour hairnylonwoolfursilkpape
  rcottonhard rubberpolyesterpolyvinylchloride
  (PVC)plastic
• -

7
Charge Distribution

• Charge gathers on the outside of conductors
• Whats the best way to hide from lightning?

8
Newtons Law of Universal Gravitation

• To understand electrical forces, we will first
  compare them to gravitational forces.
• Every object in the universe attracts every other
  object with a force that is directly proportional
  to the mass of each body and inversely
  proportional to the distance between them.
• Fg Gm1m2/d2 (m mass, d distance)
• G 6.67 x 10-11 Nm2/kg2

9
Inverse Square Law
10
Coulombs Law

• The electrical force between two charged bodies
  is directly proportional to the charge on each
  body and inversely proportional to the square of
  the distance between them.
• FE kEq1q2/d2 (q charge, d distance)
• kE 9 x 109 Nm2/C2

11
Coulombs Law

• Difference from universal gravitation Force can
  be attractive OR repulsive!

12
The Coulomb

• Electric charge is measured in Coulombs in the
  metric system.
• We will not be using the English system for
  electricity! (No one does!)
• 1 C 6.24 x 1018 electrons
• Thats 6,240,000,000,000,000,000 electrons!
• We usually deal with micro Coulombs (10-6 C)

13
Gravitational and Electric Fields

• Both forces act over a distance by altering the
  space around them
• Michael Faraday came up with the concept of a
  field around objects
• The influence they objects have on each other can
  be represented with vector arrows or field lines.
• Field doesnt depend on the test mass or test
  charge

14
Gravitational and Electric Fields

• g Fg / m
• Where g is gravitational field strength
• Gravitational field lines always point to the
  center of the Earth (always attractive)

• E FE / q
• Where E is the electric field strength
• Electrical field lines always point away from
  positive and towards negative charges (using a
  positive test charge)

15
Gravitational and Electric Fields
16
Potential

• When you lift a book, you give it the potential
  to fall (change its motion)
• Measured from the reference point of the ground.

• When you put a charge in an electric field, you
  give it the potential to change its motion
• Measured from a reference point in the field

17
Potential Difference

• In a gravitational field, the potential
  difference depends on the Earths field strength
  and the height above the ground
• In an electric field, the potential difference
  depends on the electric field strength and the
  distance between the charges
• ?V Ed
• Where ?V is potential difference

18
Potential Difference

• It is also called Voltage because it is measure
  in Volts.
• Like fluids, when there is a potential
  difference, charges want to flow until they are
  balanced out.
• Potential difference is the prime mover in the
  electrical system.

19
Current

• In a fluid system, a current can be maintained by
  a pump.
• In an electrical system, a current of charges can
  be maintained by a voltage source.
• How do we get a potential difference (voltage)?

20
Galvani vs Volta
Animal Electricity vs. Chemical reactions
21
Voltas Pile
i.e. The Battery
22
Types of Batteries

• Dry Cell (Primary)
• Wet Cell (Secondary)
• To make a battery, you just need two different
  metals and an electrolyte solution (like salt
  water or acid)

23
Batteries Environmental Issues

• Americans use an average of 5 cordless products
  per day (RBRC 2004).
• In 2005, around 200 million cell phones were in
  use in the U.S. with 130 million cell phones
  discarded annually (Eartheasy 2004).
• Disposal of cell phone batteries
• Landfills Leakage from single cell phone battery
  can pollute up to 158,000 gal of water
• Incinerators If burned, batteries release toxic
  gases into atmosphere.
• Recycling programs Verizon, ATT

24
Voltage Sources

• Battery or Generator
• The anode is positive.
• The cathode is negative.
• Batteries
• Primary cells - not easily rechargeable
• Secondary cells - easily recharged
• DC vs AC
• A voltmeter is used to measure voltage or
  potential difference.

25
Voltage Sources

• Why are there different sizes of batteries when
  most have the same voltage?
• Larger ones store more chemicals, so the
  reactions can keep going for a longer time.
  Smaller equipment uses smaller size.

26
Circuits
27
Circuits

• Circuit elements
• Voltage source
• Conductive connectors (complete loop!)
• Load
• Control switch (optional)

28
Series Voltage Sources

• When connected from anode to cathode, the voltage
  from one battery aids the voltage from another
• Add the voltages of each battery in series aiding
  to find total voltage
• Voltage sources in series opposing (cathode to
  cathode or anode to anode) subtract

29
Potential Drop

• High potential at the anode
• Low potential at the cathode
• Drops by a certain amount through each load