PHY 1020 – Chapter 6: Electricity and Magnetism

What are the four fundamental forces of nature?

Strong, Electromagnetic, Weak, and Gravitational forces.

Which exchange particle mediates the strong nuclear force?

Gluons.

Which property determines whether a particle feels the electromagnetic force?

Electric charge.

Electric charge comes in how many basic types and what are they called?

Two types: positive and negative.

Is electric charge conserved?

Yes, the total charge in an isolated system remains constant.

What is the smallest unit of quantized charge?

The charge of one electron, −1.6 × 10⁻¹⁹ C.

Define electric current.

The rate of flow of charge; measured in amperes (Coulombs per second).

What electrical quantity is measured in volts?

Electric potential (voltage), the energy per unit charge.

State Ohm’s law in its most common form.

V = I R (voltage equals current times resistance).

Why do static-electric shocks rarely harm you even at tens of thousands of volts?

Because the current delivered is extremely small (≈1 mA), so the power is tiny.

Household power in the U.S. is typically supplied at what voltage and current limit?

About 110 V up to roughly 100 A.

How is electric power calculated?

P = V I (power equals voltage times current).

Differentiate AC and DC current in one sentence.

AC periodically reverses direction, whereas DC flows in a single constant direction.

Who championed AC transmission and ultimately won the “War of Currents”?

Nikola Tesla.

Why is AC preferred for long-distance power transmission?

Transformers can easily step AC voltages up or down, allowing high-voltage, low-current transmission with reduced losses.

What protective devices stop excessive current in household circuits?

Fuses and circuit breakers.

Write the formula for power loss in transmission lines.

P_loss = I² R.

Why are transmission lines run at very high voltage?

To lower the current and thus reduce I²R power losses.

Approximate voltage and current of a lightning strike?

~10 million volts and ~100,000 amps.

What fundamental source produces magnetism at the atomic level?

Moving electric charge, particularly electron spin and orbital motion.

What are ferromagnets?

Materials in which atomic magnetic moments align permanently, creating a strong permanent magnet.

What happens at the Curie temperature of a ferromagnet?

Thermal agitation destroys the alignment, eliminating permanent magnetism.

Have magnetic monopoles been observed in nature?

No, only magnetic dipoles have been observed so far.

Why are rare-earth magnets so strong?

Their atoms contain many unpaired electrons in outer shells, producing large magnetic moments.

How does an electromagnet create a magnetic field?

A current through a wire generates a surrounding magnetic field (right-hand rule).

What geophysical structure acts like a giant electromagnet protecting Earth from solar particles?

Earth’s magnetic field generated by its molten, moving iron core.

Write the transformer voltage relation for an ideal transformer.

Vs / Vp = Ns / Np (voltage ratio equals turns ratio).

What device converts electrical energy into mechanical work using magnetism?

An electric motor.

What is the electromagnetic counterpart of a motor that converts mechanical work into electricity?

An electric generator or dynamo.

How is digital data stored on magnetic media?

Binary information is encoded by the orientation (up/down) of tiny magnetic domains.

What are eddy currents?

Loops of induced current in a conductor caused by a changing magnetic field, which create opposing magnetic fields and dissipate energy as heat.

Define a superconductor.

A material that exhibits zero electrical resistance below a critical temperature (T_c).

Why can superconductors enable magnetic levitation?

They expel magnetic fields (Meissner effect) and can carry large currents, creating strong opposing magnetic forces.

Give one practical application of magnetic levitation.

High-speed maglev trains.

What three major regions make up the U.S. power grid?

Eastern Interconnect, Western Interconnect, and Texas (ERCOT).

Which parameter (voltage or current) is more dangerous for causing deep tissue burns and fibrillation?

Current; even small currents (~100 mA