Physics: Electricity and Electric Charge

• Physics is a natural science that studies matter, its motion, and behavior through space and time, and that studies the related entities of energy and force.

Electricity

• Electricity is the set of physical phenomena associated with the presence and motion of electric charge.
• Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwell's equations.
• Various common phenomena are related to electricity, including lightning, static electricity, electric heating, electric discharges and many others.
• The presence of electric charge, which can be either positive or negative, produces an electric field.
• The movement of electric charges is an electric current, which produces a magnetic field.

Electric Charge

• Electric charge is a fundamental physical property of matter that causes it to experience a force when placed in an electromagnetic field.
• Electric charge can be positive or negative.
• Like charges repel each other, and unlike charges attract each other.
• Electric charge is a conserved quantity; the total charge of an isolated system remains constant.
• The SI unit of electric charge is the coulomb (C).
• An electron has a charge of approximately -1.602 × 10⁻¹⁹ C; a proton has a charge of +1.602 × 10⁻¹⁹ C.

Electric Field

• An electric field is a vector field that associates to each point in space the force that would be exerted on a unit positive electric charge at that point.
• Electric fields are produced by electric charges or by changing magnetic fields.
• The electric field is defined as the electric force per unit charge.
• The SI unit for the electric field strength is volts per meter (V/m) or equivalently newtons per coulomb (N/C).

Electric Potential

• Electric potential is the amount of work needed to move a unit positive charge from a reference point to a specific point inside the field without producing any acceleration
• It is measured in volts (V), where 1 volt is equal to 1 joule per coulomb (1 V = 1 J/C).
• Electric potential is a scalar quantity.
• The potential difference between two points is called voltage.

Capacitance

• Capacitance is the ability of a body to store an electrical charge.
• Capacitance is measured in farads (F), where 1 farad is equal to 1 coulomb per volt (1 F = 1 C/V).
• A capacitor is a device designed to store electric charge.
• The capacitance of a capacitor depends on its geometry and the material between its conductors.

Current

• Electric current is the rate of flow of electric charge past a point or region.
• It is measured in amperes (A), where 1 ampere is equal to 1 coulomb per second (1 A = 1 C/s).
• Current is typically carried by moving electrons in a conductor, such as a wire.
• Current can also be carried by ions in an electrolyte or by both ions and electrons in a plasma.
• Current flows from a point of high electric potential to a point of low electric potential in a circuit.
• There are two types of current: direct current (DC) and alternating current (AC).
  • In direct current, the flow of electric charge is only in one direction.
  • In alternating current, the direction of flow of electric charge reverses periodically.
• The magnitude of current is given by: I = ΔQ/Δt, where I is the current, ΔQ is the amount of charge flowing, and Δt is the time interval.

Voltage

• Voltage, also known as electric potential difference, electric pressure or electric tension is the difference in electric potential between two points.
• It is measured in volts (V), where 1 volt is equal to 1 joule per coulomb (1 V = 1 J/C).
• Voltage is the driving force that pushes electric charge through a circuit.
• Voltage is related to current and resistance by Ohm's law: V = IR, where V is the voltage, I is the current, and R is the resistance.

Resistance

• Electrical resistance is a measure of the opposition to the flow of electric current in an electrical circuit.
• It is measured in ohms (Ω), where 1 ohm is equal to 1 volt per ampere (1 Ω = 1 V/A).
• Resistance depends on the material, length, and cross-sectional area of the conductor.
• Materials with high resistance are called insulators, while materials with low resistance are called conductors.
• Ohm's Law: V = IR where V is the voltage across the resistor, I is the current through the resistor, and R is the resistance of the resistor.

Electrical Circuits

• An electrical circuit is a closed loop that allows electric current to flow.
• A simple circuit consists of a voltage source, a resistor, and a conducting path.
• Circuits can be series or parallel.
  • In a series circuit, components are connected end-to-end, so the same current flows through each component.
  • In a parallel circuit, components are connected side-by-side, so the voltage across each component is the same.
• Kirchhoff's Laws are fundamental to circuit analysis:
  • Kirchhoff's Current Law (KCL): The sum of currents entering a node (junction) is equal to the sum of currents leaving the node.
  • Kirchhoff's Voltage Law (KVL): The sum of the voltage drops around any closed loop in a circuit is equal to zero.

Electrical Power

• Electrical power is the rate at which electrical energy is transferred by an electric circuit.
• It is measured in watts (W), where 1 watt is equal to 1 joule per second (1 W = 1 J/s).
• Power is related to voltage and current by the equation: P = VI, where P is the power, V is the voltage, and I is the current.
• Power can also be expressed as P = I²R or P = V²/R, where R is the resistance.
• Electrical energy consumption is typically measured in kilowatt-hours (kWh).

Magnetism

• Magnetism is a class of physical phenomena that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments.
• Magnetic fields exert a force on moving electric charges.
• Magnetism is closely related to electricity, and the two are aspects of electromagnetism.

Electromagnetism

• Electromagnetism is the interaction between electric and magnetic fields.
• It is described by Maxwell's equations, which relate electric and magnetic fields to each other and to electric charges and currents.
• Electromagnetic waves, such as light, radio waves, and X-rays, are disturbances in electric and magnetic fields that propagate through space.
• Electromagnetism is one of the four fundamental forces of nature (the others being the strong nuclear force, the weak nuclear force, and gravity).

Measuring Instruments

• Ammeter: Measures the current flowing through a circuit, connected in series.
• Voltmeter: Measures the voltage across a component in a circuit, connected in parallel.
• Ohmmeter: Measures the resistance of a component, with the component isolated from the circuit.
• Multimeter: Measures voltage, current, and resistance.

This section covers electricity as a physical phenomenon associated with electric charge. It explores the relationship between electricity and magnetism and common electrical phenomena. It also defines electric charge as a fundamental property of matter and its interaction with electromagnetic fields.