Understanding Electricity: Static, Current, Circuits, and More

Posted on Feb 16, 2025 in Physics

Topic 1: Early Models of Electricity

Two-fluid model (late 1700s) (Dufay)

  • Explained two kinds of charges caused by varying amounts of two fluids called vitreous and resinous.
  • A neutral object had equal amounts of both fluids.

One-fluid model (1752) (Franklin)

  • Explained a charged object as having an excess or deficiency of electrical fluid.
  • A neutral object would have the proper amount of fluid.

Topic 2: Atomic Structure and Charge

  • Atoms are made of subatomic particles such as protons, which are stationary, and electrons, which are able to move.
  • When an object is charged by friction, one material removes loosely held electrons from the other material.
  • So, one becomes negative and the other positive.
  • A conductor allows electrons to move easily.
  • In an insulator, electrons do not move easily.
  • Like charges repel and unlike charges attract.

Topic 3: Methods of Charging Objects

There are 3 ways an object can become charged:

  1. Friction – Rubbing
  2. Conduction – Charge transfer by touching. Objects have the same charge.
  3. Induction – Charge transfer by bringing nearby. Objects have opposite charge.


Topic 4: Electroscopes and Electrophorus

  • The electroscope has the following functions:

    • Detecting the presence of an electric charge

    • Determining the kind of charge

    • Estimating the size of the charge

  • The electrophorus will easily and quickly charge an object over and over again.

Topic 5: Static vs. Current Electricity

  • Static electricity is the build-up of electric charge on an object.

  • Current electricity is the movement of electric charge.

  • Charges move in electrostatics and current electricity.

  • In static electricity, the movement is in brief bursts.

  • In current electricity, the movement is a continuous flow.

Topic 6: Electric Cells – Wet and Dry

  • The main parts of any electric cell are two different metals surrounded by an acid or salt.

  • A wet cell, such as the voltaic cell, uses two different metal strips placed in an acid or salt solution.

  • A dry cell, such as a battery, does not use a liquid solution.


Topic 7: Electric Circuits and Current

  • An electric cell contains a positive and negative electrode.

  • They are connected by a conducting loop, or circuit, through which electrons travel from negative to positive.

  • Circuits can be closed or opened by a switch.

  • Electric current is a rate of electron flow in a circuit.

  • Charge is the amount of electrons.

  • An ammeter measures the amount of electric current.

Topic 8: Electric Potential and Voltage

  • Electric potential energy is the stored energy when a circuit is open and the work done when a circuit is closed.

  • Since electrons flow from negative to positive, high potential is located at the negative electrode and low potential at the positive electrode.

  • The difference between these electrodes is the electric potential difference, or voltage.

Topic 9: Sources of Electrical Energy

  • Five sources of electrical energy are:

    1. Chemical energy

    2. Thermoelectric energy

    3. Photoelectric energy

    4. Piezoelectric energy

    5. Electromagnetic energy


Topic 10: Basic Circuit Components

  • A basic circuit consists of:

    1. Source of energy (battery)

    2. Conducting loop (copper wire)

    3. Load (appliance or resistor)

  • Cells can be connected in series and parallel.

  • Series – one flow of electrons

current is same / voltage adds up

  • Parallel – many paths for electrons

current adds up / voltage is same

Topic 11: Resistance to Electron Flow

  • Resistance is the ability of a pathway to oppose the flow of electrons.

    • Length – longer pathway, more resistance

    • Width – narrower, more resistance

    • Type of material – stronger insulator, more resistance

    • Temperature – hotter, more resistance

Resistance is the ratio of voltage over current.

Topic 12: Household Circuits

  • Household circuits:

    • Use alternating current

    • Operate at 120 V or 240 V

    • Are connected in parallel

  • Circuit breakers and fuses protect against an overload and short circuits.


Topic 13: Power & Energy in Your Home

  • Power is the rate at which work is produced, absorbed, or transferred.

  • 2 formulas:

  • The kilowatt hour (kWh) is the amount of energy transmitted by 1000 W in an hour.