Electricity and Electric Charge Quiz

Electricity

• Electricity is a form of energy caused by charged particles (electrons and protons). It can be static (built up) or dynamic (moving).
• Atoms are the fundamental units of matter, composed of electrons, protons, and neutrons.
• The negatively charged electrons orbit a positively charged nucleus (protons and neutrons).
• A free electron is one that has enough energy to leave its parent atom.
• Electrical charge results from an imbalance of electrons; an excess creates a negative charge, a deficiency a positive charge.
• Static electricity is the presence of a net charge in a material.
• Lightning is a large static electricity spark between charges in the atmosphere.

Electric Charge

• An electron has a negative charge equal in magnitude to a proton's positive charge.
• Opposite charges attract, like charges repel.

Static Electricity

• Rubbing objects together can transfer electrons, creating static charges on the objects.

AC and DC

• AC (Alternating Current): current periodically reverses its direction. Used in long-distance power transmission because of lower energy loss.
• DC (Direct Current): current always flows in one direction. Efficient for low-voltage applications such as electronics.

Atomic Structure (revisited)

• The number of protons (positive charges) in an atom is equal to the number of electrons (negative charges), in a stable atom.
• Copper is a commonly used metal in electrical systems.
• The arrangement of electrons in shells determines the chemical properties of an element.

Generation of AC Voltage

• An alternating voltage continually changes in magnitude and periodically reverses in polarity.
• Alternators are generators that produce AC voltage.
• Electromagnetic induction is the process of producing a voltage by changing the magnetic field around a coil.

DC Generators

• Faraday’s Laws of Electromagnetic Induction are the physical concepts behind the creation of DC voltage.
• A conductor that cuts the flux of a magnetic field will induce an EMF (electromotive force), which causes a current flow when connected to a circuit.

Magnetism

• Magnetism is the phenomenon of attractive or repulsive forces between materials.
• Magnets have north and south poles, and opposite poles attract.
• Magnetic fields are created by moving electric charges.
• A coil of wire with current produces a magnetic field.
• The magnetic field of a coil resembles that of a permanent disk magnet.

Electricity and Magnetism

• Electricity and magnetism are interconnected.
• A current generates a magnetic field and vice versa.

Current (revisited)

• Current (I) is the rate of flow of charge. Measured in Amperes (A).
  • I = Q/t (charge/time)

Voltage (revisited)

• Voltage (V) is the energy or work per unit charge (in joules per coulomb) - measured in Volts (V).
  • V = W/Q (work/charge)

Resistance

• Resistance (R) opposes the flow of current. Measured in Ohms (Ω).
• Factors determining resistance include material, length, cross-sectional area and temperature.
• Resistance (R) is related to resistivity, length and cross sectional area: R=ρL/A, where:
• ρ = resistivity
• l = length
• A = area

Temperature Effects on Resistance

• Resistance typically increases with rising temperature for most conductors.
• Temperature coefficients of resistance describe how resistance changes with temperature.

Power

• Power (P) is the rate at which energy is used. Measured in Watts (W).

• P = W/t [energy/time]

• P = VI = I²R = V²/R, where:
• V= voltage; 

• I = current;

• R = resistance

Ohm's Law

• Ohm's law relates voltage, current, and resistance: V=IR

Kirchhoff's Laws

• Kirchhoff's Current Law (KCL): The sum of currents entering a junction equals the sum of currents leaving the junction.
• Kirchhoff's Voltage Law (KVL): The sum of voltage drops around any closed loop in a circuit equals zero.

Methods of Analysis

• Useful for analyzing circuits with multiple voltage and current sources and variables:
• Nodal Analysis: Finds unknown voltages at various points.
• Branch Current Method: Uses currents in branches.
• Loop Current Method: Utilizes currents in closed loops.