Quiz

How do astronomers measure cosmic elemental abundances, and why does it matter?

They measure emission/absorption lines in light from cosmic objects. Each element’s “fingerprint” reveals how much is present, crucial for testing Big Bang models and understanding universe evolution chemically.

What are the cosmic abundances of hydrogen, helium, and everything else?

About 90% hydrogen, 9% helium, and ~1% all other elements.

How do temperature and energy density change as the universe expands?

Both drop with expansion (lower density, lower temperature). If compressed, both increase.

What happens if you heat an atom or a nucleus enough?

Electrons get stripped off (ionization), and at higher temperatures (~10^9 K), the nucleus breaks into protons and neutrons.

Which eras did particle, nuclear, and atomic physics dominate, and when?

Particle Physics: <1 second after the Big Bang; Nuclear Physics: ~1 second to 300,000 years; Atomic Physics: ~300,000 years onward.

What are alpha, beta, and gamma radiation, and which is the most dangerous?

Alpha: Helium nuclei (least penetrating); Beta: High-energy electrons (medium); Gamma: High-energy photons (most penetrating and usually most dangerous externally).

What is the basic model of the atom, and how big is the nucleus compared to the whole atom?

A tiny nucleus of protons/neutrons in the center, electrons around it. The nucleus is thousands of times smaller—like a blade of grass in a stadium.

How do a cloud chamber and a Geiger counter detect radiation?

Cloud Chamber: Vapor condenses along charged particle tracks; Geiger Counter: Ionized gas causes an electrical pulse.

What is the electric force law?

F = k (q1 q2) / r^2, an inverse-square force that can attract or repel, depending on the charges’ signs.

What is an isotope, and how can you find protons, neutrons, and electrons from its symbol?

Isotopes have the same number of protons but different neutrons. In A_ZX: Z = protons = electrons, A = protons + neutrons, Neutrons = A - Z.

What is a half-life, and how does radioactive dating work?

Half-life: time for half a radioactive sample to decay; in dating, remaining radioactive isotopes indicate how long since material stopped exchanging isotopes.

What are the ages of the Earth and the universe?

Earth is about 4.5 billion years old; the universe is about 13.8 billion years old.

What holds the nucleus together, and what is binding energy?

The strong nuclear force overcomes proton repulsion; binding energy is the mass difference released when nucleons fuse into a nucleus.

Compare nuclear fission vs. fusion, and explain chain reactions.

Fission: Splitting heavy nuclei (e.g., uranium) can cause a chain reaction. Fusion: Fusing light nuclei (e.g., hydrogen) into heavier, both releasing energy.

What are peaceful and non-peaceful applications of fission and fusion?

Fission: Nuclear power reactors (peaceful), atomic bombs (non-peaceful); Fusion: Research reactors for clean energy (peaceful), hydrogen bombs (non-peaceful).

How does the universe’s expansion produce hydrogen and helium?

After the Big Bang, as the universe cooled, protons/neutrons fused to form helium, setting the ~90% H / ~9% He ratio.