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Understanding Voltage and Current: Atoms, Electrons, and Batteries, Slides of Electrical Circuit Analysis

An in-depth exploration of voltage and current, starting with the atomic structure of matter, the concept of potential energy, and the definition of voltage. It then delves into the role of electrons as charge carriers, safety considerations when dealing with electricity, and various types of voltage sources, including batteries and solar cells. The document also covers the concept of ampere-hours and the differences between conductors, insulators, and semiconductors.

Typology: Slides

2012/2013

Uploaded on 03/17/2013

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Chapter 2 Voltage and Current
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Download Understanding Voltage and Current: Atoms, Electrons, and Batteries and more Slides Electrical Circuit Analysis in PDF only on Docsity!

Chapter 2 – Voltage and Current

2.2 – Atoms and Their Structure

  • Nucleus
    • Protons
    • Electrons
    • Neutrons

2.3 - Voltage

  • The flow of charge is established by an external

“pressure” derived from the energy that a mass

has by virtue of its position: Potential energy

  • Energy: the capacity to do work
    • If a mass (m) is raised to some height (h) above a reference plane, it has a measure of potential energy expressed in joules (J) that is determined by
    • W (potential energy) = mgh where g is the gravitational acceleration (9.8 m/s^2 )

Voltage

  • A potential difference of 1 volt (V) exists

between two points if 1 joule (J) of energy is

exchanged in moving 1 coulomb (C) of charge

between the two points

  • The unit of measurement volt was chosen to

honor Alessandro Volta

Voltage

  • Notations for sources of voltage and loss of

potential

  • E - Voltage sources (volts)
  • V - Voltage drops (volts)
  • Potential – The voltage at a point with respect

to another point in the electrical system.

Typically the reference point is the ground,

which is at zero potential.

Voltage

  • Potential difference: The algebraic difference in potential (or voltage) between two points of a network.
  • Voltage: When isolated, like potential, the voltage at a point with respect to some reference such as ground.
  • Voltage difference: The algebraic difference in voltage (or potential) between two points of a system. A voltage drop or rise is as the terminology would suggest.
  • Electromotive force (emf): The force that establishes the flow of charge (or current) in a system due to the application of a difference in potential.

2.4 - Current

  • The free electron is the charge carrier in a copper

wire or any other solid conductor of electricity

  • With no external forces applied, the net flow of

charge in a conductor in any one direction is zero

  • Basic electric circuit

Current

  • Safety considerations
    • Even small levels of current through the human body can cause serious, dangerous side effects
    • Any current over 10 mA is considered dangerous
    • currents of 50 mA can cause severe shock
    • currents over 100 mA can be fatal
    • Treat electricity with respect – not fear

Voltage Sources

  • dc Voltage sources
    • Batteries (chemical action)
    • Generators (electromechanical)
    • Power supplies (rectification)

Voltage Sources

  • Batteries: combination of two or more similar

cells

  • A cell being a fundamental source of electrical energy developed through the conversion of chemical or solar energy
  • All cells are divided into Primary and Secondary types - Primary type is not rechargeable - Secondary is rechargeable; the cell can be reversed to restore its capacity - Two most common rechargeable batteries are the lead-acid unitDocsity.com

Voltage Sources

  • Alkaline primary cells
    • Powered zinc anode (+)
    • Potassium (alkali metal) electrolyte
    • Manganese dioxide, carbon cathode (–)

Voltage Sources

  • Lead-acid secondary cell
    • Sulfuric acid is the electrolyte
    • The electrodes are spongy lead (Pb) and lead peroxide (Pb0 2 )

Voltage Sources

  • Solar cell
    • A fixed illumination of the solar cell will provide a fairly steady dc voltage for driving loads from watches to automobiles
    • Conversion efficiencies are currently between 10% and 14%

Voltage Sources

  • Ampere-hour rating
    • Batteries have a capacity rating in ampere-hours
    • A battery with an ampere-hour rating of 100 will theoretically provide a steady current of 1A for 100 h, 2A for 50 h or 10A for 10 h
    • Factors affecting the rating: rate of discharge and temperature - The capacity of a dc battery decreases with an increase in the current demand - The capacity of a dc battery decreases at relatively (compared to room temperature) low and high temperatures