EP SCI Midterm 1

[L3] What is ordinary matter made of?

Atoms; their structure and interactions determine the properties of materials.

[L3] What are the main parts of an atom?

A nucleus containing protons and usually neutrons, surrounded by electrons. Proton number identifies the element.

[L3] How do mass and weight differ?

Mass is the amount of matter, measured in kilograms. Weight is gravitational force and changes with local gravity.

[L3] How do volume and density differ?

Volume is space occupied. Density is mass divided by volume; typical SI units are kg/m³, not kg/m.

[L3] What is a molecule?

Two or more atoms chemically bonded together, such as H₂O, CH₄, or O₂.

[L3] Does finding organic molecules prove life exists?

No. Organic compounds are carbon-based, commonly with hydrogen, and can form through nonliving chemistry.

[L3] What does temperature describe?

A material's thermal state; for an ideal gas it tracks average random particle kinetic energy. It is not the total energy of the whole object.

[L3] Why use kelvin in radiation formulas?

Kelvin is an absolute temperature scale. Convert approximately by adding 273 to Celsius; temperature ratios must use kelvin.

[L3] What is pressure?

Force per unit area. In a gas, particle collisions transfer momentum to surfaces and produce pressure.

[L3] What determines whether a substance is solid, liquid, or gas?

Both temperature and pressure; a phase diagram maps the stable phases.

[L3] How do solids, liquids, and gases differ in particle arrangement?

Solid particles remain near fixed positions; liquid particles stay close but move past one another; gas particles spread throughout available space.

[L3] What is plasma?

An ionized state of matter containing mobile charged particles, including free electrons and ions.

[L3] How do molecular dissociation and ionization differ?

Dissociation breaks a molecule into smaller components. Ionization removes or adds electrons, producing charged particles.

[L3] What is sublimation?

A direct change from solid to gas without an intervening liquid phase; it can occur under conditions where liquid is not stable.

[L3] What is a triple point?

The particular temperature and pressure where solid, liquid, and gas phases of a substance coexist in equilibrium.

[L3] What is the critical point on a liquid–gas phase diagram?

The endpoint of the liquid–gas boundary; beyond its temperature and pressure, there is no distinct liquid–gas phase separation.

[L3] What is electromagnetic radiation?

Energy carried by changing electric and magnetic fields; light has both wave and particle properties.

[L3] What is a photon?

A packet of electromagnetic energy. Its energy depends on its frequency, not simply on how bright a beam is.

[L3] How do wavelength and frequency differ?

Wavelength is the distance between wave crests; frequency counts cycles per second. At fixed wave speed, shorter wavelength means higher frequency.

[L3] How does wavelength affect photon energy?

Shorter wavelength means greater energy per photon. Halving the wavelength doubles photon energy.

[L3] Order electromagnetic radiation from highest to lowest photon energy.

Gamma rays, X-rays, ultraviolet, visible, infrared, microwaves, radio. Wavelength increases in the opposite direction.

[L3] What does it mean for atomic energy levels to be quantized?

Only certain energy levels are allowed; an electron cannot take an arbitrary energy between those levels.

[L3] When does an atom absorb or emit a photon?

Absorption raises its energy; emission lowers it. The photon energy must match an allowed energy-level difference.

[L3] What is the difference between excitation and ionization?

Excitation raises an electron to a higher bound energy level. Ionization removes an electron from an atom, producing a charged ion.

[L3] Why do spectral lines identify elements?

Different elements have characteristic allowed energy transitions, producing distinct patterns of absorption and emission wavelengths.

[L3] How do fluorescence and stimulated emission differ?

Fluorescence emits light after excitation. Stimulated emission occurs when a photon triggers an excited system to emit a matching photon; it is the basis of lasers.

[L3] What is thermal radiation?

Electromagnetic radiation emitted because of temperature. A warm object emits across a range of wavelengths, not just one wavelength.

[L3] What does Wien's law predict?

Hotter objects peak at shorter wavelengths. For this course, peak wavelength in micrometers is approximately 3,000 divided by temperature in kelvin.

[L3] What does the Stefan–Boltzmann law predict?

For a blackbody, emitted power per unit area increases as temperature in kelvin to the fourth power. Doubling temperature increases it 16-fold.

[L3] How do the Sun's and Earth's thermal spectra differ?

The Sun peaks near visible wavelengths; Earth peaks in infrared. This difference is central to the greenhouse effect.

[L3] What is the cosmic microwave background (CMB)?

Relic thermal radiation from the early universe, now observed at about 2.7 K. Its spectrum supports a hot, dense early universe.

[L3] Why could light travel freely after recombination?

Electrons combined with nuclei to form neutral atoms, greatly reducing scattering by free electrons. This occurred about 380,000 years after the Big Bang.

[L3] Why is early-universe light observed as microwaves today?

Expansion stretched its wavelength and cooled the radiation. This is cosmological redshift.

[L3] How do dark matter and dark energy differ?

Dark matter is inferred from gravitational effects on matter and light. Dark energy describes the component associated with accelerated cosmic expansion; neither is simply ordinary unseen gas.

[L3] How do reflection, absorption, and transmission differ?

Reflection redirects light away; absorption transfers its energy to matter; transmission lets light pass through material.

[L4] What makes a hypothesis scientific?

It makes testable predictions that can be compared with observations and potentially contradicted.

[L4] How does a scientific theory differ from an everyday guess?

A scientific theory is a broad explanation supported by substantial evidence and successful tests, not merely an unsupported opinion.

[L4] Can supporting observations prove a hypothesis forever?

No. Evidence can strongly support it, but new observations may require revision or rejection.

[L4] Why is science described as self-correcting?

Claims are checked against evidence, measurements can be repeated, and explanations are revised when they fail tests.

[L4] What is confirmation bias?

Favoring evidence or interpretations that agree with existing beliefs while neglecting conflicting evidence.

[L4] What is the false consensus effect?

Overestimating how many other people share your own opinions or beliefs.

[L4] How do geocentric and heliocentric models differ?

Geocentric models place Earth at the center of planetary motions; heliocentric models place the Sun at the center of the planetary system.

[L4] What is apparent retrograde motion?

A planet temporarily appears to move backward relative to background stars because Earth and the planet are moving in their orbits; the planet does not reverse its actual orbital direction.

[L4] What were epicycles used to explain?

Small circular motions superimposed on larger circles were used to reproduce apparent planetary motions, including retrograde motion.

[L4] What connected Tycho Brahe's observations with Kepler's advances?

Precise measurements let Kepler test and revise orbital models. Better data distinguished explanations that rough observations could not.

[L4] What observations support formation of the solar system from a disk?

Mostly coplanar, same-direction, nearly circular planetary orbits; systematic composition differences; and consistent ages of primitive material.

[L4] What are isotopes?

Atoms of the same element with the same proton number but different neutron numbers.

[L4] How do radioactive decay, fission, and fusion differ?

Radioactive decay is spontaneous nuclear change. Fission splits a heavy nucleus; fusion joins light nuclei. Not all radioactive decay is fission.

[L4] What is a half-life?

The time for half the radioactive parent nuclei in a large sample to decay. Each additional half-life halves the remaining parent amount.

[L4] How do meteorites help establish the solar system's age?

Radioisotopic dating of primitive meteorites dates early solar-system solids to about 4.6 billion years ago.

[L4] What is a nebula, and what drives its collapse?

A cloud of gas and dust. Gravity drives contraction when it overcomes pressure support.

[L4] Which cloud conditions favor gravitational collapse?

Greater mass, greater density, and lower temperature favor collapse; warmer gas provides stronger thermal pressure support.

[L4] Why does a collapsing cloud heat up?

Gravitational potential energy is converted into motion and thermal energy during contraction.

[L4] Why does a contracting cloud spin faster?

Its angular momentum is approximately conserved as its size decreases, like a skater pulling inward while spinning.

[L4] Why does a rotating cloud form a flattened disk?

Rotation resists inward motion perpendicular to the rotation axis, while collisions dissipate disordered motion. Material settles into a rotating plane.

[L4] Why can star-forming clouds look dark or glow?

Dust can block background starlight. Gas illuminated and ionized by hot young stars can emit light and glow.

[L4] What is the Jeans mass concept?

A threshold cloud mass for gravitational collapse under specified temperature and density conditions. Hotter or less dense clouds require more mass to collapse.

[L4] What direct evidence supports ongoing star and planet formation?

Observed young stars surrounded by disks and clusters at different developmental stages show that formation is observable, not only inferred from our solar system.

[L5] How do terrestrial planets and gas giants differ in bulk composition?

Terrestrial planets are mainly rock and metal. Gas giants contain massive hydrogen-helium envelopes around deeper interiors.

[L5] What is the basic sequence of planet growth?

Dust grains collect into larger bodies, planetesimals grow into protoplanets, and continued accretion builds planets.

[L5] What is accretion?

Growth by collecting surrounding material through collisions, sticking, and gravitational attraction.

[L5] How do planetesimals and protoplanets differ?

Planetesimals are relatively small planetary building blocks. Protoplanets are larger growing bodies assembled from them.

[L5] What is the frost line or snow line?

The distance in a young disk beyond which a particular volatile, commonly water, can remain frozen. It is a formation boundary, not the habitable zone.

[L5] Why did ice help giant planets form?

Beyond the frost line, extra solid material helped cores grow large enough to capture substantial hydrogen and helium before the disk gas dispersed.

[L5] Why is Jupiter not a star?

It lacks enough mass to sustain ordinary hydrogen fusion in its core.

[L5] What is the traditional circumstellar habitable zone?

The range of distances where a planet could maintain surface liquid water under suitable atmospheric conditions; it does not guarantee life.

[L5] How do habitable and inhabited differ?

Habitable means capable of supporting life; inhabited means life actually exists there.

[L5] How does stellar luminosity affect the habitable zone?

More luminous stars have habitable zones farther out; less luminous stars have them closer in. The zone can shift as a star evolves.

[L5] Why are surface liquid water and orbital distance not the whole habitability story?

Atmosphere, climate stability, chemistry, energy supply, and subsurface environments also matter.

[L5] Why can an object outside the traditional habitable zone still contain liquid water?

Internal heat can maintain water below an icy surface even when sunlight is too weak to maintain surface liquid water.

[L5] Why might long-lived stars and stable planetary conditions favor life?

They can provide sustained suitable conditions and time for life to originate and evolve; these are favorable conditions, not proof of life.

[L5] Why does received starlight decrease with the square of distance?

The same luminosity spreads across a sphere whose area increases with distance squared. Twice as far receives one-quarter the flux.

[L5] What is albedo, and how does it affect absorbed sunlight?

Albedo is the fraction reflected. Higher albedo means less absorbed energy and a lower equilibrium temperature, all else fixed.

[L5] What sources may have contributed Earth's water?

Water-bearing planetesimals and hydrated minerals contributed material; outgassing also transferred water from Earth's interior to its surface and atmosphere.

[L5] What helps a planet retain atmospheric gases?

Stronger gravity and lower temperature favor retention; lighter gas particles at a given temperature move faster and are generally easier to lose.

[L5] Why are dust grains and comets relevant to prebiotic chemistry?

Grains provide surfaces and shielding for molecular chemistry; icy small bodies can preserve and deliver organic compounds. Organics do not by themselves prove life.

[L5] Why do greenhouse molecules absorb selected infrared wavelengths?

Their allowed rotational and vibrational energy transitions match particular infrared photon energies.

[L5] How does the greenhouse effect warm a surface?

Gases absorb and emit infrared radiation, changing how heat escapes to space. The surface and lower atmosphere warm until the planet regains energy balance.

[L6] Is Earth's mantle liquid?

It is mostly solid silicate rock, but it can deform and flow over long timescales. Convection transfers internal heat.

[L6] How do lithosphere and asthenosphere differ?

The lithosphere is the rigid outer layer, including crust and uppermost mantle. The underlying asthenosphere is weaker and can deform slowly.

[L6] How do Earth's inner and outer core differ?

The inner core is solid; the outer core is liquid. Very high pressure helps keep the inner core solid despite its high temperature.

[L6] What generates Earth's magnetic field?

Motion of electrically conducting liquid metal in the outer core sustains a dynamo that generates the magnetic field.

[L6] Why does Earth's magnetic field matter for its environment?

It redirects many charged solar-wind particles and affects how the planet interacts with space; it is not a shield against all radiation.

[L6] What are subduction and seafloor spreading?

Subduction carries a plate down into the mantle. Seafloor spreading forms new oceanic lithosphere at divergent mid-ocean ridges.

[L6] Where do many earthquakes, volcanoes, and mountain-building events occur?

Near plate boundaries, where plates converge, separate, or slide past one another. Some volcanism also occurs within plates.

[L6] What is the carbonate–silicate cycle?

Long-term carbon recycling through volcanic release, silicate weathering, ocean sediment formation, and tectonic recycling.

[L6] How can weathering provide a negative climate feedback?

Warmer, wetter conditions can speed silicate weathering, drawing down CO₂ and opposing warming. The response depends on conditions and operates slowly.

[L6] Why cannot the geological carbon cycle quickly offset rapid CO₂ emissions?

Its major stabilizing processes operate over hundreds of thousands to millions of years, much slower than rapid human emissions.

[L6] How do ice cores preserve evidence of past atmospheres?

Trapped air bubbles preserve samples of earlier atmospheric gases, allowing past CO₂ concentrations to be measured.

[L6] What does ppm mean for an atmospheric gas?

Parts per million: for example, 300 ppm means about 300 molecules of that gas per million air molecules.

[L6] What is positive feedback?

A response that amplifies an initial change. Warming can thaw permafrost and release greenhouse gases, producing further warming.

[L6] Does positive feedback mean beneficial, and negative feedback mean harmful?

No. Positive amplifies a change; negative counteracts it. These labels do not judge whether the outcome is desirable.

[L6] What are two major causes of warming-related sea-level rise?

Thermal expansion of seawater and addition of water from melting land ice. Melting already-floating ice has little direct effect.

[L6] How does added atmospheric CO₂ cause ocean acidification?

Some CO₂ dissolves and alters seawater chemistry, increasing acidity and making carbonate shell formation more difficult.

[L6] How can warming reduce oxygen availability in water?

Warmer water generally holds less dissolved oxygen, which can stress aquatic organisms.

[L6] What is the water-vapor feedback involved in a runaway greenhouse?

Warming increases evaporation; water vapor adds greenhouse warming, encouraging further evaporation. Under sufficient forcing, oceans can be lost.

[L6] What is the basic climate contrast among Earth, Venus, and Mars?

Earth supports widespread surface liquid water; Venus has an extremely hot, dense CO₂ atmosphere; Mars has a cold, thin atmosphere unfavorable for persistent exposed liquid water.

[L6] What indicates that Mars had a wetter past?

Ancient channels and other water-shaped landforms indicate past liquid-water activity, even though present surface conditions differ greatly.

[L6] What causes tidal forces?

Gravity differs across an extended object: the near side is pulled more strongly than the far side, producing differential stretching.

[L6] How do orbital resonance and eccentricity help generate tidal heating?

Resonances can maintain noncircular orbits. Changing gravitational stretching repeatedly deforms the moon, dissipating mechanical energy as heat.