HW - #4 Review

The Sun is so hot that its material is in the form of a _________. Gravity is always producing a force that tends to make the Sun collapse toward its center. To balance this force, the energy produced by nuclear fusion produces an outward _________, allowing the Sun to be in a condition of ___________. Inside the Sun, energy is transported via __________, where hot material rises and cooler material falls downward. Energy is also transported outward via ____________, but photons take between 100,000 and 1,000,000 years to reach the Sun's surface. On the other hand, ________ produced by nuclear fusion at the center reach the surface of the Sun in just a little more than 2 seconds.

1. Plasma 2. pressure 3. equilibrium 4. convection 5. radiation 6. neutrinos

The source of the Sun's energy was only identified in the 20th century; before that, humans enjoyed sunshine without having any explanation of its source. Today we know that the source of the Sun's energy is the conversion of mass into ________, through the process of nuclear ________. For this process to start, temperatures in the core of a star must be at least __________ degrees. If the temperature is hot enough, two protons (hydrogen nuclei) can turn into a ___________ nucleus, an antimatter particle called a __________, and a ______________. This is the first step in a three-step sequence of nuclear reactions that astronomers call the _______________.

1. energy 2. fusion 3. 12 million 4. deuterium 5. positron 6. neutrino 7. proton-proton chain

The Sun converts 4 × 109 kg of mass to energy every second. How many years would it take for the Sun to convert 6 × 1024 kg (the mass of the Earth) into energy?

4.760×10^7 years

The Sun emits energy at a rate 3.8 × 1026 joules per second. If for every kg of hydrogen converted to helium 0.0071 kg is converted to energy, what mass of hydrogen (in kg) must be consumed every second to fuel the Sun?

5.947×10^11 kg

The discovery that stars, and by extension the Sun, are composed largely of hydrogen and helium is the result of the doctoral work of

Cecilia Payne-Gaposchkin

Hottest Zone of the Sun

Core

Today we realize that the source of energy for the Sun is a process called

Nuclear Fusion

What is NOT a product of the first step in the p-p chain of nuclear fusion?

a form of helium

According to the formula E=mc2,

a little bit of mass can be converted into a substantial amount of energy

What will take the shortest time to emerge from the Sun's photosphere (surface)?

a neutrino (3 seconds)

The typical time it takes a photon to go from the center of the Sun to the edge of the Sun is about ten years.

false

What is NOT one of the fundamental particles that we find inside atoms?

positrons

A college friend of yours who has been postponing taking any science courses hears you talking about the generation of nuclear energy in the Sun and makes the following observation: "The whole idea of the atomic nucleus is pretty ridiculous. If an oxygen nucleus consists of eight protons and eight neutrons, the charge on that nucleus is positive. Since even I learned in high school that like charges repel, such a nucleus would find all its positive protons repelling and quickly fall apart." How would you answer his argument?

the nuclear force, which is attractive over short distances like the nucleus, and stronger than electricity, holds the nucleus together

Although the Sun is about 4.5 billion years old, many of the protons in its core have not yet been involved in fusion reactions.

true

How do astronomers know what the outer layers of the Sun are made of?

we take an absorption line spectrum of the Sun, and the absorption lines tell us what elements are present in the outer layers