Electricity, Magnetism, and Electromagnetism

Converts electrical energy (kinetic energy of electrons) into electromagnetic energy (x-ray photons).
This conversion occurs when high-speed electrons strike a target material.
The energy conversion is highly inefficient for x-ray production: approximately 99% of the electrical energy is converted to heat, while only 1% results in x-ray photons.

The study of stationary or resting electric charges.
Electric charges are fundamental properties of matter:
- Positive charge: Associated with protons in the atomic nucleus.
- Negative charge: Associated with electrons orbiting the nucleus.
- The elementary charge of an electron is approximately $-1.6 \times 10^{-19} C$ , and a proton is $+1.6 \times 10^{-19} C$ (Coulombs).
Electrification methods:
- Contact: Transfer of electrons from one object to another through direct touch.
- Friction: Transfer of electrons between two objects rubbed together (e.g., rubbing a balloon on hair).
- Induction: Redistribution of electric charges in an object due to the proximity of another charged object, without direct contact.

Law of Charges: Unlike charges attract each other, while like charges repel each other.
Coulomb's Law: The electrostatic force ( $F$ ) between two charged objects is directly proportional to the product of their magnitudes ( $q1$ and $q2$ ) and inversely proportional to the square of the distance ( $r$ ) between their centers.
- Mathematically, $F = k \frac{|q1 q2|}{r^2}$ , where $k$ is Coulomb's constant.
Conservation of Charge: Electric charge cannot be created or destroyed; it can only be transferred from one object to another.
Quantization of Charge: Electric charge exists in discrete units, meaning it is found in integer multiples of the elementary charge (the charge of a single electron or proton).

The study of electric charge in motion (electric current).
Materials are classified by their ability to conduct electrons:
- Conductors: Materials that allow electrons to flow easily due to loosely bound outer-shell electrons (e.g., copper, silver, aluminum).
- Insulators: Materials that resist the flow of electrons due to tightly bound electrons (e.g., rubber, glass, plastic).
- Semiconductors: Materials with conductivity between that of conductors and insulators; their conductivity can be altered by external conditions or doping (e.g., silicon, germanium).
Superconductivity: A phenomenon where certain materials exhibit zero electrical resistance and expel magnetic fields below a critical temperature, allowing electron flow without energy loss (e.g., niobium-titanium alloys).

A controlled pathway for the flow of electrons.
Key electrical quantities:
- Current (I): The rate of flow of electric charge, measured in Amperes (A). $I \propto$ to the number of electrons flowing per unit time.
- Voltage (V): The electric potential difference or electromotive force (EMF) that drives the current, measured in Volts (V).
- Resistance ($\Omega$): The opposition to the flow of electric current, measured in Ohms ($\Omega$).
Ohm's Law: Describes the relationship between voltage, current, and resistance: $V = IR$ .

Direct Current (DC): Electrons flow continuously in one single direction from the negative terminal to the positive terminal of a power source (e.g., batteries).
Alternating Current (AC): Electrons oscillate back and forth periodically, reversing their direction of flow at regular intervals. This type of current is typically used in household and industrial power grids.

Superconductors: Materials that offer no resistance to electron flow below a critical temperature (e.g., Niobium-Titanium).
Conductors: Materials that readily permit electron flow (e.g., Copper, Gold, Silver).
Semiconductors: Materials with variable conductivity that can be manipulated (e.g., Silicon, Germanium used in electronics).
Insulators: Materials that strongly resist electron flow (e.g., Rubber, Glass, Wood).

Arises from the motion of electric charges, specifically the spin and orbital motion of electrons within atoms.
Magnetic fields are always dipolar, meaning they always have both a north and a south pole; isolated magnetic poles do not exist.
Types of magnets:
- Natural Magnets: Occur naturally in nature (e.g., Lodestone - naturally magnetized magnetite).
- Artificial Permanent Magnets: Man-made magnets that retain their magnetic properties after being magnetized (e.g., bar magnets, alnico).
- Electromagnets: Temporary magnets created by coiling a wire around a ferromagnetic core and passing an electric current through the wire; magnetic field strength is controllable.

Ferromagnetic materials (e.g., iron, nickel, cobalt) can be temporarily or permanently magnetized when placed in an external magnetic field.
The strength of a magnetic field is measured in tesla (T) or gauss (G).
- 1 Tesla (T) = 10,000 Gauss (G).
- The Earth's magnetic field is approximately 0.5 G.

The fundamental force that describes the interaction between electricity and magnetism, unified by scientists in the 1700s and 1800s (e.g., Oersted, Faraday, Maxwell).
Electromagnetic Induction: The process by which an electric current is generated in a conductor when it is exposed to a changing magnetic field. This principle is governed by Faraday's Law of Induction, which states that the magnitude of the induced electromotive force (EMF) is proportional to the rate of change of magnetic flux.

Motor: A device that converts electrical energy into mechanical energy (motion). It operates on the principle that a current-carrying conductor in a magnetic field experiences a force (Lorentz force).
Generator: A device that converts mechanical energy into electrical energy. It operates on the principle of electromagnetic induction, where rotating a conductor in a magnetic field induces an electric current.

A device designed to change (transform) alternating current (AC) voltages and currents from one level to another without changing the frequency or type of energy.
It operates on the principle of mutual induction between two coils (primary and secondary) wound around a common ferromagnetic core.
Transformer Law (Turns Ratio): The ratio of the secondary voltage ( $V2$ ) to the primary voltage ( $V1$ ) is equal to the ratio of the number of turns in the secondary coil ( $N2$ ) to the number of turns in the primary coil ( $N1$ ).
- Mathematically: $\frac{V1}{V2} = \frac{N1}{N2}$ or $\frac{VS}{VP} = \frac{NS}{NP}$ .
- Step-up transformer: Increases voltage (N2 > N1); decreases current.
- Step-down transformer: Decreases voltage (N2 < N1); increases current.
Transformers are crucial for efficient transmission of electrical power over long distances.