Untitled Flashcard Set
Section 1: Electricity
1. Charged Particles & History of the Atom
Observation of Electric Force: Rubbing materials (like amber) creates an attraction to small objects (feathers/paper).
Importance: Early discovery of static electricity; foundation for understanding electric charges.
William Gilbert (1600): Named the phenomenon “electric force” (from Greek “elektron” = amber).
Importance: Introduced systematic study of electricity.
Atoms & Elements: Matter is made of atoms (indivisible particles). Modern understanding: atoms have subatomic particles (protons, neutrons, electrons).
Importance: Understanding atomic structure is crucial because electricity comes from the movement of electrons.
2. Benjamin Franklin’s Contributions
Electrical Fire: Franklin experimented with Leyden jars, observed attraction & repulsion.
Importance: Introduced the idea that electric charge is conserved—cannot be created or destroyed, only transferred.
Kite Experiment: Showed lightning is electrical in nature.
Importance: Established connection between natural phenomena and electricity.
3. Electrons, Protons, Neutrons
Structure of Atom:
Nucleus: protons (positive) + neutrons (neutral)
Electrons (negative) orbit nucleus
Electric Charge: Protons (+), electrons (–), neutrons (0). Opposites attract, likes repel.
Importance: Explains why electrons move and why electricity exists.
Electron Movement: Electrons accelerate more than protons due to lower mass (Newton’s laws).
Importance: Movement of electrons is the main source of electric current.
4. Fundamental Forces & Mass
Four fundamental forces: Gravity, electric, strong nuclear, weak nuclear.
Importance: Electric force is dominant at atomic scale; gravity negligible in atoms.
Gravity vs Electric Force: Gravity is weak (at atomic level), electricity is extremely strong.
Importance: Explains why atoms stick together via electric forces, not gravity.
5. Coulomb’s Law
Formula:
FE = electric force, q1/q2 = charges, r = distance, k = Coulomb constant
Electric Charge is Quantized: Smallest charge = 1.7 × 10⁻¹⁹ C (proton/electron).
Importance: Fundamental for quantum physics; explains why charges are discrete.
Like charges repel, opposite charges attract.
Importance: Explains interactions between charged objects.
6. Electric Fields
Definition: A field assigns a value to every point in space due to a phenomenon.
Vector fields = magnitude + direction; scalar fields = magnitude only.
Electric Field (E): Force per unit charge at a point:
Positive charges move with the field, negative charges move opposite.
Superposition: Electric fields from multiple charges add vectorially.
Importance: Helps calculate forces in systems with many charges.
Dipoles: Molecules can have positive/negative sides, creating fields even if overall neutral.
Importance: Explains chemical interactions & molecular behavior.
7. Symmetry & Gauss’s Law
Using Symmetry: Helps simplify calculations of electric fields for multiple charges.
Example: Two equal charges → field at midpoint = 0.
Gauss’s Law:
Relates total electric flux through a surface to total charge inside.
Importance: Simplifies calculation of electric fields for symmetric objects (plates, spheres).
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Section II: Circuits
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ENERGY
1. Kinetic and Potential Energy
Energy: In physics, energy is the ability to do work. Measured in joules (J).
Conservation of Energy: Energy cannot be created or destroyed—only transformed.
Kinetic Energy (KE): Energy of motion (e.g., a moving baseball).
Gravitational Potential Energy (GPE): Energy due to position in a gravitational field (e.g., a stone in the air).
Energy transformation: KE can become GPE and vice versa (e.g., pendulum swings). Total energy stays constant.
Heat: Energy in transit due to temperature difference; heat flows from hot → cold (2nd Law of Thermodynamics).
Temperature: Measures average kinetic energy of particles in a substance.
3rd Law of Thermodynamics: Absolute zero cannot be reached (atoms cannot fully stop moving).
Friction: Converts kinetic energy into heat that cannot be converted back into motion.
2. Electric Potential Energy
Similar to gravitational potential energy but caused by electric forces.
Energy transforms between kinetic and electric potential energy in charged particles.
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VOLTAGE (Electric Potential)
Voltage (V): Difference in electric potential between two points. Measured in volts (V = J/C).
Electric potential vs. electric potential energy:
Potential energy = energy of a charged object.
Potential (voltage) = energy per charge; describes the environment.
Analogy: Like a topographic map:
Steeper hills = stronger electric field.
Equipotential lines = same voltage.
Voltage is analogous to height in gravitational systems; charge is analogous to weight.
Voltage (V) and energy (E) relationship:
\Delta E = q \times V
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BATTERIES
Early experiments: Galvani → Volta → battery invention.
Battery: Maintains voltage by separating positive and negative charges.
Primary cells: One-use, chemical reaction produces charge (e.g., lemon battery).
Secondary cells: Rechargeable (e.g., lithium-ion batteries).
Lithium-ion batteries: Ions move back and forth during charging; some energy lost as heat.
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SIMPLE CIRCUITS
Circuit: Closed loop allowing electricity to flow.
Fluid analogy:
Water flow ↔ electric current
Pump ↔ battery
Pressure difference ↔ voltage
Current (I): Rate of charge flow; measured in amperes (A = C/s).
Direction convention: positive current flows opposite to electron movement.
Direct Current (DC): Current flows in a single direction.
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ELECTRICITY AND SAFETY
Small currents can be fatal (0.07 A can be lethal).
Voltage creates the potential for current, but current is what actually harms.
Body signals are electrical; high currents disrupt heart or nerve signals.
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OHM’S LAW
I = \frac{V}{R}
Resistance resists current flow (like friction in wires):
Conductors → low resistance
Insulators → high resistance
Higher voltage → higher current (for a given R)
Safety: High voltage isn't always dangerous if current is limited.
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POWER
Power (P): Rate of energy transfer; measured in watts (W = J/s).
P = \frac{E}{t}
Energy bills measure kilowatt-hours:
1 \text{ kWh} = 3,600,000 \text{ J}
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Section III: Magnetism and Electromagnetism:
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1. Basic Properties of Magnets
Poles: Magnets have north (N) and south (S) poles. Like poles repel, opposite poles attract.
Magnetic dipoles: Cutting a magnet in half creates two smaller magnets; there are no magnetic monopoles.
Atomic magnetism: Individual atoms act as tiny dipoles. In ferromagnetic materials (like iron, nickel), atoms align and create permanent magnetism. In paramagnetic materials, atoms align only temporarily in the presence of a magnetic field.
Key visualizations: Magnetic field lines exit the north pole and enter the south pole; compass needles align with the magnetic field.
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2. Magnetic Fields and Motion
Origin: Magnetic fields are produced by moving charges (electrons/protons). Stationary charges produce electric fields only.
Direction: The magnetic field is perpendicular to the motion of the charge and forms closed loops around the moving charge.
Right-hand rule: Thumb = current/velocity, fingers = field direction.
Important points: Motion is relative; whether a magnetic field appears depends on the observer's frame of reference.
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3. Earth's Magnetism
Earth acts as a giant magnet due to electric currents in its molten iron core (dynamo effect).
Earth's magnetic poles are slightly offset from geographic poles. The magnetic poles wander and occasionally reverse polarity.
Compasses point toward Earth's magnetic south pole (which is near the geographic North Pole).
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4. Protective Role of Earth's Magnetic Field
Shields Earth from solar wind and coronal mass ejections (CMEs).
Deflects charged particles, preventing atmospheric loss.
Charged particles interacting with the atmosphere create auroras (green = oxygen, purple = hydrogen).
Planets without strong magnetic fields (e.g., Mars) lose atmosphere and water more easily.
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5. Magnetic Force
Equation:
Only affects moving charges.
Direction: perpendicular to both velocity and magnetic field .
Circular motion: Magnetic force deflects particles, causing centripetal motion without changing speed (used in mass spectrometers).
Right-hand rule for force: Index finger = velocity, fingers = magnetic field, thumb = force direction.
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6. Magnetic Fields from Currents
Current-carrying wire: Produces a magnetic field in loops around the wire (right-hand rule).
Ampère’s Law: , field strength decreases with distance from wire.
Solenoids: Looped wire currents reinforce magnetic fields, resembling a bar magnet.
for field inside solenoid.
Applications: MRI machines, electromagnets.
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7. Electromagnetic Induction (Faraday’s Law)
Changing magnetic fields can generate electric currents (moving magnet or changing field).
Steady magnet cannot generate current; motion or change is required.
Discovered by Michael Faraday (1831).
Section IV: Electromagnetic Waves
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1. Unification in Physics
Key idea: Physics breakthroughs often come from unifying seemingly different phenomena under one principle.
Examples:
Newton’s laws: explain both falling apples and planetary motion.
Maxwell’s unification: electricity + magnetism + light.
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2. Maxwell’s Equations (Conceptual Overview)
Gauss’s Law (electric field): Electric fields arise around charges.
Gauss’s Law for Magnetism: No magnetic monopoles exist (magnetic field lines always form loops).
Faraday’s Law: Changing magnetic fields create electric fields.
Ampere-Maxwell Law: Currents or changing electric fields create magnetic fields.
Maxwell’s discovery: Light is an electromagnetic wave; changing electric and magnetic fields propagate as waves.
Analogy: Proton moving back and forth → creates ripples of electric & magnetic fields, just like a duck swimming creates water ripples.
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3. Wave Mechanics
Wave definition: Transfer of energy without transport of matter.
Types of waves:
Longitudinal: vibration in direction of wave (sound waves).
Transverse: vibration perpendicular to wave (guitar string, electromagnetic waves).
Wave properties:
Wavelength (λ): Distance between two peaks.
Amplitude: Height → intensity/brightness/loudness.
Frequency (f): Wavelengths per second (Hz).
Wave speed (v):
Sound vs Light:
Sound needs a medium; light does not → light can travel in a vacuum.
Light travels at .
and inversely related: , .
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4. Electromagnetic Spectrum
Visible light: 400 nm (blue) – 700 nm (red).
Other EM waves:
Infrared: heat, emitted by warm objects.
Microwaves/Radio waves: communication, Wi-Fi.
Ultraviolet (UV): sunburn, can damage skin/materials.
X-rays: penetrate soft tissue, absorbed by bones.
Gamma rays: radioactive nuclei, very high energy.
Key concept: All are electromagnetic waves; only differ in wavelength and frequency.
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5. Polarization
Definition: Direction of electric field oscillation in a transverse wave.
Applications:
Polaroid sunglasses: reduce glare (absorb horizontal polarized light).
3D movies: two images polarized differently → each eye sees one image → brain perceives depth.
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6. Long-Distance Communication
History:
Hertz: proved EM waves exist.
Marconi: first wireless transatlantic signal.
Modern uses: Radio, TV, internet, satellites.
Radio telescopes: Focus waves to “see” distant objects and detect invisible radiation (e.g., Cosmic Microwave Background, infrared, UV).
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7. Radio and TV Signals
Radio: Converts sound (kHz) → electromagnetic waves (MHz).
AM: amplitude changes with sound.
FM: frequency changes with sound.
Television:
CRT: electrons deflected onto screen → light bursts.
LCD: uses polarization of light to control pixel brightness.
Color: pixels are red, green, blue → mix to create all visible colors.
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8. LEDs and Solar Power
LEDs:
Semiconductor emits light when electrons move energy levels.
Efficient: less heat, longer lasting.
RGB LEDs → white light.
Solar panels:
Convert light → electricity using semiconductors.
Can detect nonvisible light (e.g., infrared).
Potential future: large-scale solar electricity, powering spacecraft.
Light sails: Use sunlight for propulsion (tiny but cumulative force).