Electricity

Electric Charge is a Basic Characteristic of Matter

• Electrons are a negatively charged particle in all molecules

  • Electrons can transfer between objects

• Example: Rub a ballon against your hair

  • Electrons move from your hair to the ballon and give it a charge​

  • If you put two charged balloons next to each other, the electrons in one will repel the electrons in the other

Electric Charge is a Basic Characteristic of Matter

• Rule One Electricity: Like Charges Repel one another

  • Two negative electrons will repel one another

• Rule Two of Electricity: Unlike Charges attract each other

• Atomic Structure

  • Electrons are outside of a nucleus in a cloud, and move about freely

    • Electrons can travel from atom to atom and form ions

      • If an atom gains an electron, it becomes more negative charged

      • if an atom loses an electron, it becomes more positive charged

  • The nucleus is made up of positive charged protons and neutral neutrons

• When charges change on something, the total charge remains the same, electrons are not created or destroyed

Coulomb's Law

• Electrical force has a pattern much like gravitational force

  • Depends on the Quantity of the charged particles and is inversely related to the square of the distance between the particles​

  • Electrical constant k= 9 x 10⁹

  • q₁= charge one

  • q₂= charge two

  • d=distance

• The unit we measure charge in is the Coulomb (C)

  • 1 C = 6.25 billion electrons, the amount that passes through a 100 watt lightbulb in less than a second​

Electric Current

• Just like with heat, the loose electrons in metals make them good conductors of electricity

• Electric Current-the flow of electrons in one direction

  • Rate of electric flow is measured in amperes (A)

• Current is produced by voltage

  • Voltage is the relationship between an electron's potential energy and quantity of charge

    • Electrons flow through a circuit because of the voltage across the circuit​

Electrical Resistance

• The amount of electron flow depends on the the voltage and electrical resistance

  • Resistance is anything that resist the flow of the current

    • The width of the wire, length of a wire, and material used all impact the resistance

• Measured in ohms (Ω)

Ohm's Law

• Current is impacted by two factors: Voltage and Current

• In Circuits with constant resistance, the current and voltage are proportional to each other

  • Double the voltage, you double the current​

• Many devices include resistors in order to keep them from receiving too much of a current

Direct Current and Alternating Current

• Direct Current (dc): electrons flow only in one direction, from negative terminal to positive terminal

  • Speed is slow because electrons are constantly bumping each other

• Alternating Current (ac): electrons flow in one direction, and then in the opposite direction​

  • Better for high powered devices

  • Most ac circuits involve currents that alternate back and forth at a rate of 60 cycles per second

Electric Power

• The movement in an electrical current does work

  • Electrical energy may be transformed to mechanical energy, light, thermal energy, as well as other forms

• Electric Power=current x voltage​

Electric Circuits

• any path that electrons can travel across is a circuit

  • Steady currents need a complete circuit with no gaps

    • Switches are gaps that can be filled in to complete a circuit when needed​

• There are two Types of circuits

  • Series

  • Parallel​

Series Circuits

• The Electric Current has only one pathway

  • Current is the same in all parts of the circuit

  • If one part of the path fails, the current stops

• The total resistance is equal to the sum of the individual resistances in the current path

• The current follows ohms law

• The total voltage divides among all stops in the circuit​

  • Voltage drop across each device is proportional to the resistance​

Parallel Circuits

• Each device is connected to the same two points across the circuit, making the voltage the same for each device

• The total current divides along the branches

  • The current in each branch is inversely proportional to the resistance on that branch

• The total current is equal to the sum of each branches current

• As the number of branches increase the overall resistance decreases​

Parallel Circuits and Overloading

• As more devices are added to a parallel circuit, the overall resistance of the circuit goes down

  • This can lead to a circuit having a current that is too high for it to handle leading to an electrical fire

• To prevent overloading, most circuits have circuit breakers that will open a switch if the current gets to be too high