"The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is electrical conductance, measuring the ease with which an electric current passes."
Introduction to electrical current, resistance and Ohm's law, factors affecting resistance, Kirchhoff's laws, resistivity and conductivity.
Electric Fields: The region around a charged object where it exerts a force on other charges.
Coulomb's Law: The law which states that the force of attraction or repulsion between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
Electric Potential Energy: The potential energy associated with a charge due to its position in an electric field.
Electric Potential: The electric potential energy per unit charge at a point in an electric field.
Conductors and Insulators: Materials that allow or resist the flow of electric charge, respectively.
Ohm's Law: The law which states that the current passing through a conductor between two points is directly proportional to the voltage across the two points, provided the temperature and other physical conditions remain constant.
Resistivity: The property of a material that determines its resistance to electric current.
Resistance: The measure of the degree to which a material opposes the flow of electric current.
Power: The rate at which energy is transferred or consumed per unit of time.
Series Circuits: Circuits in which elements are connected in a single pathway, so that the current flows through each element in turn.
Parallel Circuits: Circuits in which elements are connected in multiple pathways, so that the current splits and flows through each element independently.
Kirchhoff's Laws: Two laws that govern the behavior of circuits, which relate to the conservation of charge and energy.
Junction Rule: The rule which states that the sum of the currents entering a junction is equal to the sum of the currents leaving the junction.
Loop Rule: The rule which states that the sum of the changes in potential around any closed loop in a circuit is equal to zero.
RC Circuits: Circuits that contain a resistor and a capacitor, which are used in a variety of applications, including filters and timers.
Magnetic Fields: The area around a magnet where magnetic force can be detected.
The Lorentz Force: The force exerted on a charged particle in a magnetic field.
Magnetic Induction: The process by which an electric current is induced in a conductor when it is moved across a magnetic field.
Faraday's Law of Induction: The law which states that the induced voltage in a circuit is proportional to the rate of change of the magnetic field through the circuit.
Lenz's Law: The law which states that the direction of an induced current is such that it opposes the change that produced it.
Transformers: Devices that use electromagnetic induction to transfer electrical energy from one circuit to another.
AC and DC Circuits: Circuits that use alternating-current or direct-current power sources, respectively.
Electromagnetic Waves: Waves that consist of oscillating electric and magnetic fields, which propagate through space.
Maxwell's Equations: A set of four equations that govern the behavior of electromagnetic fields.
Applications of Electricity and Magnetism: A variety of practical applications of electric and magnetic phenomena, including motors, generators, transformers, communication systems, and medical devices.
Direct Current (DC): The flow of electric charge in one direction only.
Alternating Current (AC): The flow of electric charge that periodically reverses direction.
Pulsed Direct Current: A series of direct current pulses in which the direction of current flow is not uniform.
Leakage Current: The current that flows through electrical insulation or a semiconductor that is not intended to conduct electricity.
Ohmic Resistance: A resistance that is independent of the current and voltage applied across it.
Non-Ohmic Resistance: A resistance that changes with the current and voltage applied across it.
Variable Resistance: A resistance whose value can be changed easily, such as a rheostat or potentiometer.
Negative Resistance: A resistance in which the current decreases as voltage is increased, creating a voltage drop across it opposite to that of a conventional resistor.
Superconductivity: A state in which a material has zero resistance to the flow of electrical current.
Temperature Coefficient of Resistance: The measure of how much the electrical resistance of a material will change with temperature.
Direct Magnetic Current (DMC): The flow of magnetic charge in one direction only.
Alternating Magnetic Current (AMC): The flow of magnetic charge that periodically reverses direction.
Pulse Magnetic Current: A series of magnetic current pulses in which the direction of the magnetic charge flow is not uniform.
Eddy Current: A flow of electric charge induced within conductors by a changing magnetic field in proximity.
Magnetic Permeability: A property of a material that determines its ability to conduct magnetic flux.
Saturation: A limit to how much magnetic flux can be added to a magnetic material without further increasing its magnetic field strength.
Hysteresis: A phenomenon in which a material's magnetic state lags behind changes in the magnetic field, resulting in energy loss.
Anisotropy: A property of a material that exhibits different behavior along different axes in a magnetic field.
"The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in siemens (S) (formerly called the 'mho' and then represented by ℧)."
"Objects made of electrical insulators like rubber tend to have very high resistance and low conductance, while objects made of electrical conductors like metals tend to have very low resistance and high conductance."
"This relationship is quantified by resistivity or conductivity."
"It also depends on the size and shape of an object because these properties are extensive rather than intensive."
"All objects resist electrical current, except for superconductors, which have a resistance of zero."
"The resistance R of an object is defined as the ratio of voltage V across it to current I through it."
"For a wide variety of materials and conditions, V and I are directly proportional to each other, and therefore R and G are constants (although they will depend on the size and shape of the object, the material it is made of, and other factors like temperature or strain). This proportionality is called Ohm's law."
"In other cases, such as a transformer, diode or battery, V and I are not directly proportional."
"The ratio V/I is sometimes still useful and is referred to as a chordal resistance or static resistance since it corresponds to the inverse slope of a chord between the origin and an I–V curve."
"In other situations, the derivative dV/dI may be most useful; this is called the differential resistance."
"Its reciprocal quantity is electrical conductance."
"The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in siemens (S) (formerly called the 'mho' and then represented by ℧)."
"Objects made of electrical insulators like rubber tend to have very high resistance and low conductance."
"Objects made of electrical conductors like metals tend to have very low resistance and high conductance."
"It also depends on the size and shape of an object because these properties are extensive rather than intensive."
"All objects resist electrical current, except for superconductors, which have a resistance of zero."
"The resistance R of an object is defined as the ratio of voltage V across it to current I through it."
"For a wide variety of materials and conditions, V and I are directly proportional to each other, and therefore R and G are constants."
"In other situations, the derivative dV/dI may be most useful; this is called the differential resistance."