Technological Impacts

1
March 2, 2011
DRILL

1. Pass over last nights homework.
2. Moving electrons have _______.
3. The _______ of an electric circuit uses the
   electrons ability to do work.
4. The three basic units in electricity are
   _________________________________.

Energy
Load
Voltage (V), Current (I), Resistance (R)
2
Yesterday's HOMEWORK

• Identify 5 electrical technologies not mentioned
  in class today
• (Remember, an electrical technology produces,
  stores, controls, transmits or gets work from
  electrical energy)
• Identify the problem that the technology system
  solves
• List the technological subsystems that are used
  in the technology
• Identify the technology that preceded it (i.e.
  what was used before the technology was
  invented?)

3
TERMINOLOGY

• Current (I) the motion of electrons from one
  atom to the next in a material.
• In our circuit, electrons flow from ___________
  terminal to the ___________terminal.
• This motion of electrons through our conductor
  (wire) is considered current (like water through
  a pipe).
• Materials that resist current are
• called ___________.
• Materials that provide
• a path for current are called
• ___________.
• Current is measured in AMPERES (Amps)

NEGATIVE
POSITIVE


INSULATORS

CONDUCTORS

4
TERMINOLOGY

• Voltage (V) the electric potential between two
  points of opposite charge.
• Voltage is the potential energy of the electrical
  power source.
• Voltage is measured in Volts (V).

5
TERMINOLOGY

• Resistance (R) a measure of the degree to which
  an object opposes an electric current through it
  .
• Resisting an electric current often generates
  heat.
• This is the principle behind how light bulbs
  work.
• Resistance is measured in Ohms (W the Greek
  letter Omega)

6
Ohms Law

• George Ohm (1789 1854) a high school and
  university mathematics instructor
• Discovered 1827
• Voltage Current x Resistance
• V I R
• What are the units of this formula?
• Volts Amperes x Ohms

7
Problems Ohms Law

• Copy the steps to solve this problem on your
  worksheet
• A cell phone charger converts the wall outlet
  voltage to 5 Volts to charge the cell phone. The
  amount of current that the charger outputs is .7
  Amperes. Sketch a schematic diagram of this
  circuit. What is the resistance of the cell
  phone battery?
• Write the given information
• V 5 volts
• I .7 amps
• R ?

A schematic is a diagram that represents the
elements of a system without using realistic
pictures
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Problems Ohms Law

• Write the given information
• V 5 volts
• I .7 amps
• R ?
• Sketch a schematic diagram of the circuit
• Start with power source
• Add conductors
• Add resistance
• Add current

R ?
V 5V
-
I .7A
9
Problems Ohms Law

• Write the given
• information
• V 5 volts
• I .7 amps
• R ?
• Rearrange, Substitute, and Solve

1. Sketch a schematic diagram of the circuit

V I x R R 5V / .7A R 7.14 W
R V / I
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Electrical Power

• Electric Power the rate at which electrical
  energy is transferred by an electric circuit.
• Units of power are the Watt (W)
• A human climbing a flight of stairs is doing work
  at a rate of about 200 watts.

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Joules Law

• James Joule (1818 1889) showed that heat and
  electrical energy are interchangeable.
• Joules Law
• Power Voltage x Current
• P V I
• Watts Volts x Amperes

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Problems Joules Law

• Lets look at problem 4, which is very similar
  to problem 1
• A cell phone charger converts the wall outlet
  voltage to 5 Volts to charge the cell phone. The
  amount of current that the charger outputs is .7
  Amperes. Sketch a schematic diagram of this
  circuit. What is the power used by the cell
  phone in recharging its battery?
• Write the given information
• V 5 volts
• I .7 amps
• P ?

A schematic is a diagram that represents the
elements of a system without using realistic
pictures
13
Problems Joules Law

• Write the given information
• V 5 volts
• I .7 amps
• P ?
• Sketch a schematic diagram of the circuit
• Start with power source
• Add conductors
• Add resistance
• Add current

P ?
V 5V
-
I .7A
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Problems Joules Law

• Write the given
• information
• V 5 volts
• I .7 amps
• P ?
• Write Formula, Substitute, and Solve

1. Sketch a schematic diagram of the circuit

P V I P 5V x .7A P 3.5 W
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Problems Joules Law
Complete problem 5 on your worksheet
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Problems Joules Law

• A Honda Insight (hybrid) has a 144 Volt battery
  system in its trunk. The electric motor that the
  batteries power can generate 20,000 Watts of
  power. Sketch a schematic diagram of this
  circuit. What is the current traveling through
  this high voltage circuit?
• Write the given information
• V 144 volts
• P 20,000 watts
• I ?

A schematic is a diagram that represents the
elements of a system without using realistic
pictures
17
Problems Joules Law

• Write the given information
• V 144 Volts
• P 20,000 Watts I ?
• Sketch a schematic diagram of the circuit
• Start with power source
• Add conductors
• Add load
• Add current

P 20,000 W
V 144V
-
I ?
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Problems Joules Law

• Write the given
• information
• V 144 Volts
• P 20,000 Watts I ?
• Rearrange, Substitute, and Solve

1. Sketch a schematic diagram of the circuit

P V x I I 20,000W / 144V R 138.9 A
I P / V
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CLASSWORK/HOMEWORK
Complete the worksheet on electrical problems
using Joules and Ohms Laws