Academic Decathlon Science Resource Guide

What fundamental particles make up an atom’s nucleus?

Protons and neutrons.

Which sub-atomic particle primarily moves in electric currents?

The electron.

What is the magnitude of the elementary charge on a proton or electron?

≈1.6 × 10⁻¹⁹ coulombs (with opposite signs).

State Coulomb’s Law in words.

The electric force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of their separation.

What quantity does the symbol ε₀ represent?

Permittivity of free space (8.85 × 10⁻¹² C²/N·m²).

Why are protons far less mobile than electrons in conductors?

Protons are ~1,800 times more massive, so they accelerate much less under the same force.

Give two everyday examples of static-electric phenomena.

Balloon sticking to a wall; getting shocked after walking on carpet then touching a doorknob.

Define electric field.

A vector field that assigns the force per unit positive charge at every point in space.

What direction do electric field lines point around a positive charge?

Radially outward from the charge.

What simple device demonstrates that charges reside on the outside surface of conductors?

A Faraday cage.

Name the metric unit of resistance.

Ohm (Ω).

Write Ohm’s Law.

I = V / R.

What does a battery do in a circuit?

Maintains a constant potential difference by separating positive and negative charges.

Differentiate conductors and insulators.

Conductors allow electrons to flow freely; insulators impede electron flow.

How is electric potential energy converted in an incandescent bulb?

Into thermal energy, then visible light as the filament glows hot.

Explain the function of a fuse.

It melts when current exceeds a safe value, opening the circuit to prevent overheating.

What happens to total resistance when identical resistors are added in parallel?

Total resistance decreases.

What two quantities determine the power dissipated by a resistor?

Current and voltage (P = I V).

State Faraday’s Law qualitatively.

A changing magnetic flux through a loop induces an emf (voltage) in the loop.

How does Lenz’s Law modify Faraday’s Law?

The induced current’s magnetic field opposes the change in flux that produced it.

What common household item is essentially a variable resistor actuated by heat?

A toaster (nichrome wire).

Define magnetic field.

A vector field that exerts forces on moving charges and magnetic dipoles.

Give the right-hand rule for a straight current-carrying wire.

Thumb: current direction; curled fingers: magnetic field loops around wire.

What is the unit of magnetic field strength?

Tesla (T).

Why are there no isolated magnetic monopoles observed?

Cutting a magnet always produces smaller dipoles, each with both north and south poles.

Describe a solenoid’s magnetic field inside its coils.

Nearly uniform and directed along the solenoid’s axis, like a bar magnet.

What device converts mechanical energy into electrical energy via electromagnetic induction?

A generator.

Explain transformer action in one sentence.

Alternating current in a primary coil creates a changing magnetic flux that induces a proportional voltage in a nearby secondary coil.

What determines the output voltage of a transformer?

The turns ratio V₁/N₁ = V₂/N₂.

Why is AC preferred for long-distance power transmission?

Its voltage can be stepped up (reducing current and I²R losses) or down via transformers.

State Maxwell’s great insight about light.

Light is an electromagnetic wave whose speed is determined by ε₀ and μ₀.

Give the speed of light in vacuum.

c ≈ 3.00 × 10⁸ m/s.

Define wavelength.

The spatial length of one full wave cycle between consecutive crests or troughs.

What region of the EM spectrum lies just beyond red visible light?

Infrared.

Which EM waves have the shortest wavelength?

Gamma rays.

What does polarization describe?

The orientation of the electric-field oscillations in an EM wave.

How do Polaroid sunglasses reduce glare?

They absorb horizontally polarized light reflected from surfaces.

What color results when red, green, and blue light combine?

White.

Describe the greenhouse effect in terms of EM radiation.

Glass transmits visible sunlight but blocks outgoing infrared, trapping heat.

What phenomenon explains auroras near Earth’s poles?

Solar wind particles spiral along Earth’s magnetic field, ionizing atmospheric gases that emit light.

Why doesn’t sound travel through outer space?

Sound needs a material medium; space is a vacuum.

What is the primary energy loss mechanism in incandescent bulbs?

Infrared radiation (heat).

Name the semiconductor device that emits light when current passes through.

LED (light-emitting diode).

What electrical quantity do pacemakers regulate in the human heart?

Timing of electrical pulses (current) to maintain heart rhythm.

List the four fundamental forces.

Gravity, electromagnetic, strong nuclear, weak nuclear.

What is meant by charge conservation?

Total electric charge in an isolated system remains constant.

Define capacitance.

Charge stored per volt across a capacitor (C = Q / V).

How does inserting a dielectric affect a capacitor?

Increases capacitance by reducing the internal electric field.

What causes lightning in terms of dielectric breakdown?

High voltage between cloud and ground exceeds air’s breakdown threshold, allowing current to flow.

Explain time dilation in special relativity.

Moving clocks run slower compared to stationary ones according to Δt’=γΔt.

What is length contraction?

Objects moving relative to an observer appear shortened along the direction of motion.

Why can no object reach or exceed c?

Its relativistic mass-energy would require infinite energy as speed approaches c.

What are radio waves used for in astronomy?

Mapping cold gas, pulsars, and cosmic microwave background via radio telescopes.

Name the equation linking wavelength and frequency for EM waves.

c = λ f.

What household appliance uses microwaves to heat food?

A microwave oven.

What is the resonant frequency of an LC circuit dependent on?

f = 1 / (2π√LC), where L is inductance and C capacitance.

Which historical figure coined the term ‘electricity’?

William Gilbert in 1600.

Who demonstrated that lightning is electrical using a kite experiment?

Benjamin Franklin.

What is the purpose of grounding an appliance?

Provides a low-resistance path to earth for fault currents, protecting users.

Define inverse-square law.

A physical quantity decreases proportionally to 1/r² from a source (e.g., gravity, electric force).

Give the typical drift speed of electrons in household wiring.

Less than 1 mm/s.

Why are MRI facilities cautious with metal objects?

Strong solenoid magnets (1–3 T) can turn metal into dangerous projectiles.

What did Hertz’s experiments confirm about Maxwell’s predictions?

The existence and properties of radio waves.

State the Lorentz factor γ expression.

γ = 1 / √(1 – v²/c²).

Which element dominates ordinary conductors like household wiring?

Copper.

What is meant by power factor in AC circuits?

Cosine of phase angle between voltage and current; measures real vs. apparent power.

Why are LEDs more efficient than incandescent bulbs?

They emit primarily visible photons with minimal wasted heat.

What early device stored static charge and delivered shocks for entertainment?

Leyden jar.

Identify two hazards of high current through the human body.

Loss of muscle control, ventricular fibrillation (potentially fatal).

What phenomenon allows 3-D cinema using polarizing glasses?

Each lens passes differently polarized images so each eye receives its own perspective.

Explain the function of an inductor in a circuit switched off suddenly.

It opposes the drop in current, possibly producing a voltage spike (self-induction).

Which law quantitatively links induced emf to changing magnetic flux?

Faraday’s Law (ε = –N ΔΦ/Δt).

How does a microwave’s door mesh ensure safety?

Holes smaller than microwave wavelength reflect radiation back, preventing escape.

What is a ‘light sail’?

A spacecraft propulsion method using radiation pressure from sunlight on large reflective sails.

Give the approximate magnetic field strength of Earth at the surface.

25–65 μT (microteslas).

What causes the Sun’s 11-year sunspot cycle?

Periodic twisting and realignment of the Sun’s magnetic field due to differential rotation.

Why are gamma rays hazardous to living tissue?

Their high photon energy ionizes atoms, damaging DNA.

Describe the function of a photodiode in a solar panel.

Absorbs photons to excite electrons across a p-n junction, generating current.

Which constant relates electric and magnetic fields to c?

c = 1/√(ε₀μ₀).

What is the main component of household circuit protection besides fuses?

Circuit breakers that open when current exceeds a threshold.

Define watt-hour.

A unit of energy equal to one watt of power sustained for one hour (3,600 J).

Why does resonance increase amplitude in RLC circuits?

Driving frequency matches natural frequency, causing constructive energy buildup.

What technological leap did George Westinghouse promote over Edison’s DC?

Alternating current distribution with transformers.

What discovery showed that magnetic poles reverse over geological time?

Magnetic striping on the ocean floor (seafloor spreading).

Explain why smartphones still work indoors through walls.

Radio/microwave signals penetrate many building materials that are transparent at those wavelengths.

State the principle behind an LED traffic light’s ‘always visible’ advantage.

Directional emission and rapid response time make color distinct even in bright daylight.

Which section of the EM spectrum is primarily emitted by room-temperature objects?

Infrared.

What is an arc lamp?

A lamp that emits light via a sustained electric arc between electrodes.

Who first used electromagnetic induction to generate electricity on a large scale?

Michael Faraday (1831 experiments).

Define magnetic permeability (μ).

A measure of how a material responds to and supports magnetic field formation.

Why do superconductors have zero resistance?

Electron pairs move without scattering when cooled below a critical temperature.

What does the strong nuclear force do inside atoms?

Binds protons and neutrons together in the nucleus, overriding proton repulsion.

How does Gauss’s Law simplify field calculations for symmetric objects?

It relates total enclosed charge to flux, avoiding summing individual particle effects.

Describe a Van de Graaff generator.

A belt transfers charge to a large dome, accumulating high voltages for demonstrations.

What quantity is conserved during charging by friction?

Total electric charge (conservation of charge).

Why do high-voltage lines sag on hot days?

Wire resistance heats them; thermal expansion causes sag.

What important role do magnets play in power plants?

Rotating magnets (or coils) induce emf in generators to produce electricity.

What two parameters determine the strength of gravity between masses?

Product of their masses and inverse square of separation (Newton’s law of gravitation).

Which EM band is used for Wi-Fi signals?

Microwaves (~2.4 GHz or 5 GHz).

Define ‘strong magnetic field’ in everyday terms.

Anything approaching 1 T; Earth’s field is ~10⁻⁵ T by comparison.