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.