Electrostatics and Resistivity

• Electrostatics studies phenomena associated with electric charges at rest.

Conductivity

• Measures the ease with which an electric charge moves through a material.
• Conductors allow electric charges to flow freely.
• Insulators resist the flow of electric charges.
• Semiconductors are intermediate between conductors and insulators.
• Doping improves conductivity by adding atoms of different elements to pure semiconductors.
• Superconductors offer no resistance to electric charge flow below a critical temperature, for example, hydrogen sulfide conducts charges to -70°C.

Process of Charging

• Neutral atoms have equal numbers of protons and electrons.
• Atoms gain electrons and become negatively charged, or lose electrons and become positively charged.
• Charging by friction involves rubbing two neutral bodies together; electron affinity determines the charge.
• Electron affinity measures an atom's attraction to electrons, determining its tendency to become negatively charged.
• Materials with higher electron affinity gain electrons from those with lower affinity.

Triboelectric Series

• Ranks materials based on electron affinity, materials higher on the list become positively charged when rubbed with a material lower on the list.
• Charging by conduction requires physical contact, the neutral body acquires the same charge as the charging body.
• Charging by induction charges a neutral body by proximity to a charged body, resulting in polarization.
• Grounding involves connecting the neutral body to the Earth, which can donate or accept electrons.
• An electroscope determines the electrical charge of a body.

Coulomb's Law

• The force between two small charged bodies is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
• Superposition Principle states that each charged body exerts a force on another as if no other charges are present.

Capacitors

• Capacitors are an electric component that temporarily stores energy and have Two conducting plates that face each other, separated by an insulator (dielectric).
• Capacitance (C) is the ratio of charge (Q) to potential (V), measured in farads (F).
• Factors affecting capacitance:
• Area of conducting plates: Increase increases capacitance, decrease decreases capacitance.
• Distance between conducting plates: Increase decreases capacitance, decrease increases capacitance.
• Type of dielectric: More conducting increases capacitance, less conducting decreases capacitance.

Capacitor Shapes

• Parallel-plate capacitors: capacitance depends on plate area and distance.
• Cylindrical capacitors: Inner and outer cylindrical structures with dielectric placed between.
• Spherical capacitors: Internal spherical structure covered by an outer one, capacitance varies with radius.

Capacitors in a circuit

• Series Connection:
• The Total charge is constant throughout the circuit.
• The total voltage varies and is the sum of individual voltages.
• The reciprocal of the total capacitance equals the sum of individual reciprocals.
• Parallel Connection:
• Total charge is the sum of individual charges and the total voltage is constant.
• Total capacitance equals the sum of individual capacitances.

Applications of Capacitance

• Parallel-plate capacitor capacitance depends on plate area and distance between plates.
• The formula is: C=KE(A/d), where K is the dielectric constant, A is the area, and d is the distance.

Electrodynamics: Electric Current

• Electric current is due to the movement of electrons due to electric potential energy and influenced by the electric field.
• Drift velocity is the velocity of this motion.
• Regulated flow of electrons in one direction becomes electric current.
• Drift velocity and electric current are directly proportional.
• Electric current (I) is calculated as I = q/t, where q is charge and t is time, measured in amperes (A).

Resistance and Resistivity

• An electrical conductor allows the free flow of electric current.
• Resistance limits current flow.
• Resistance and electric current are inversely proportional.
• Factors affecting resistance and current flow:
  • Electrical resistivity: Increase increases resistance, and decrease decreases resistance.
  • Electrical conductivity: Increase decreases resistance, and decrease increases resistance.
  • Temperature: Increase increases resistance, and decrease decreases resistance.
  • Length of conductor: Longer increases resistance, and shorter decreases resistance.
  • Cross-sectional area: Increase decreases resistance, and decrease increases resistance.
• Electrical resistivity is a materials intrinsic property.
• R = ρ(L/A), where ρ is resistivity, L is length, and A is cross-sectional area.

Electromotive Force

• Electromotive force (EMF) is the potential energy per unit charge to cause flow.
• EMF acts like a charge pump, measured in volts (V).
• Potential difference (PD) identifies charge flow.
• Ohm's Law
• The discovery shows the relationship among voltage, current, and resistance of the formula: V = IR.

Electric Circuits

• The Closed circuits allow current flow, and open circuits do not.
• Schematic diagrams use symbols to represent circuit components.
• A resistor is used to provide resistance.

The Series Circuit

• In Series Circuits all components are connected using a single pathway and the current is the same whereas the total voltage is the sum, and the same for total resistance
• The Parallel Circuit uses branches to allow current to pass through more than one path.
• Circuit components are either ohmic (following Ohms law) or non-ohmic
• Circuits facilitate the movement of electrical energy through current flow.
• Electrical energy passing through a higher resistance converts electrical energy into heat

Electric shock

• Electrical energy delivered through circuits can be dangerous.

Magnetism

• Magnetism attracts magnetic materials, and magnetic materials are attracted by a magnet.
• Poles are portions in a magnet where the magnetic force is greatest.
• North pole points to the north when suspended freely.
• Magnetization makes a material temporarily or permanently magnetic.

Types of Magnetic Materials

• There are three classifications of materials:
  • Ferromagnetic which are strongly attracted by a magnet.
  • Paramagnetic which are weakly attracted to magnets.
  • Diamagnetic which weakly respond to a magnetic field where magnetization exists only when an external magnetic field is applied.

Magnetic Forces and Magnetic Fields

• A magnetic field exerts a magnetic force on dipoles and electric charges.
• The formula is: F=qv x B, where F is force, q is charge, v is the velocity, and B is the magnetic field.
• The magnitude of the magnetic field: B= F/(qv sin θ).
• Tesla (T) is the SI unit for magnetic field & Gauss (G).

Electromagnetic Induction

• Produces an induced electromotive force due to a change in magnetic flux.
• Faraday's law states the induced electromotive force in a loop equals the rate of change of magnetic flux: ε= -Δφ/Δt.
• The Lenz's Law states the direction of the current induced in a conductor by a changing magnetic field, opposes the initial changing magnetic field which produced it.

Explore Coulomb's Law, electrostatic force and electrical resistivity. Problems cover force changes with distance and charge magnitude, net force calculations, and the relationship between resistivity and conductivity. Also includes resistance calculation.