JS

PHY1020-Ch06

Discovering Physics

Chapter 6 - Electricity and Magnetism

Fundamental Forces

  • Strong Force:

    • Strength: Very strong (N) (+)

    • Range: 10^-15 m (diameter of a medium-sized nucleus)

    • Mediating Particle: Gluon

    • Role: Holds nucleons (protons and neutrons) together within the nucleus.

  • Electromagnetic Force:

    • Strength: 1/137 (Weak)

    • Range: Infinite

    • Mediating Particle: Photon

    • Characteristics: Mass = 0, Spin = 1

  • Weak Force:

    • Strength: 10^-18

    • Range: 10^-6 m

    • Mediating Particles: Intermediate vector bosons (W+, W-, Z0)

    • Role: Induces beta decay.

  • Gravitational Force:

    • Strength: 6 x 10^-39 (very weak)

    • Range: Infinite

    • Mediating Particle: Graviton (hypothetical)

    • Characteristics: Mass = 0, Spin = 2

Properties of the Interactions

  • Gravitational: Acts on all masses; mediated by gravitons.

  • Weak: Acts on quarks and leptons; mediated by W and Z bosons.

  • Electromagnetic: Acts on electrically charged particles; mediated by photons.

    • Strength relative to electromagnetic: 10^-18

  • Strong Force: Acts on color charge of quarks; mediated by gluons.

    • Strength relative to electromagnetic: 10^-41

Electric Charge

  • Definition: A fundamental property of matter, akin to mass, that causes particles to exert and experience forces.

  • Types of Charge: Positive and Negative

    • Electrically neutral body: Sum of total charges = 0

    • Charge is conserved: Cannot be created or destroyed.

Electric Force

  • Electric charge creates a force when near other charges.

  • Quantized Charge: Measured in coulombs; smallest unit is the charge of an electron (1.6 x 10^-19 C)

  • Fundamental constant: ε0 = 8.854 x 10^-12 F/m

Electric Shocks – Static Electricity

  • Static shocks can range from 1,000 to 100,000 volts, but have a low current (~1 mA), resulting in low power.

Electric Current

  • Definition: The flow of electric charge, measured in amperes (A); represents how much charge flows per second.

  • Voltage: The potential energy per unit charge; Volts (V) = Joules/Coulombs.

  • Electrical Resistance: Materials resist the flow of electrons, defined by Ohm's Law: R = V/I.

Electricity in Daily Life

  • Electricity powers homes; typical household voltage: 110V with up to 100A capacity.

  • Power calculation: P = V * I = 110V * 100A = 11,000 W.

    • For example, a 110W light bulb uses about 1 A of current.

AC vs. DC Electricity

  • Alternating Current (AC): Current periodically reverses direction; efficient for long-distance transmission.

  • Direct Current (DC): Current flows in a single direction; less efficient for high-voltage transmission.

  • Edison vs. Tesla (War of Currents):

    • Edison advocated for DC; Tesla promoted AC.

    • Key figures: Edison - practical, hands-on; Tesla - theoretical, innovative.

    • Both were supposed to win Nobel Prizes in 1915, but their rivalry prevented this.

Circuit Safety: Fuses and Circuit Breakers

  • Protect circuits from excessive current which can cause overheating.

  • European standard household voltage: 220V, higher voltage necessitates careful design due to increased danger.

The Electric Grid in the US

  • Divided into three main sections: East, West, and Texas.

Power Loss in Transmission

  • Power loss occurs due to resistance in wires: P_loss = I^2 * R.

  • Example: 300A current with 2 Ohm resistance results in significant power loss:

    • P_loss = (300 A)^2 * (2 Ω) = 180,000 W (or 180 kW).

  • Conclusion: High voltage and low current minimize power loss during transmission.

Lightning and Its Dangers

  • Lightning has high voltage (up to 10 million volts) and high current (100,000 A), leading to immense power output (P = V * I = 10^12 W).

Magnets and Magnetism

  • Generated by moving charge and the intrinsic spin of electrons.

  • All magnets possess a north and south pole; like poles repel, while opposite poles attract.

Permanent Magnets

  • Created through the alignment of magnetic atoms (ferromagnets).

  • Heating a permanent magnet can reach a temperature (Curie Temperature) that destroys its magnetism.

Magnetic Monopoles

  • Hypothetical particles that would exist as isolated north or south poles, yet have not been observed.

Electromagnetic Concept

  • Electric fields and magnetic fields interact, allowing electric charge and magnets to influence each other.

Rare Earth Magnets

  • Contain more electrons in outer shells, leading to stronger magnetism compared to standard magnets.

Electromagnets

  • Produced when electric current flows through a wire, generating a magnetic field, crucial for motors and other applications.

The Earth's Magnetic Field

  • Acts as a protective barrier against harmful solar particles; studied extensively in connection with Earth’s formation.

Transformers

  • Devices that change voltage and current levels efficiently, crucial for energy distribution.

Electric Motors and Generators

  • Electric Motors: Use magnetic fields and electric currents to perform mechanical work.

  • Dynamos: Convert mechanical work into electric current (DC); Alternators for AC generation.

Magnetic Recording

  • Utilizes magnetic dipole orientation to encode binary data for storage and computation purposes.

Eddy Currents

  • Induced currents in metals when exposed to magnetic fields, applicable in various technologies.

Superconductors

  • Materials exhibiting zero electrical resistance below a critical temperature, showing promise for future technology applications.

Magnetic Levitation

  • Utilizes superconducting and electromagnets to create opposing forces, enabling maglev trains and other advanced technologies.