University Physics Volume 3

# Conceptual Questions

University Physics Volume 3Conceptual Questions

### 11.1Introduction to Particle Physics

1.

What are the four fundamental forces? Briefly describe them.

2.

Distinguish fermions and bosons using the concepts of indistiguishability and exchange symmetry.

3.

List the quark and lepton families

4.

Distinguish between elementary particles and antiparticles. Describe their interactions.

### 11.2Particle Conservation Laws

5.

What are six particle conservation laws? Briefly describe them.

6.

In general, how do we determine if a particle reaction or decay occurs?

7.

Why might the detection of particle interaction that violates an established particle conservation law be considered a good thing for a scientist?

### 11.3Quarks

8.

What are the six known quarks? Summarize their properties.

9.

What is the general quark composition of a baryon? Of a meson?

10.

What evidence exists for the existence of quarks?

11.

Why do baryons with the same quark composition sometimes differ in their rest mass energies?

### 11.4Particle Accelerators and Detectors

12.

Briefly compare the Van de Graaff accelerator, linear accelerator, cyclotron, and synchrotron accelerator.

13.

Describe the basic components and function of a typical colliding beam machine.

14.

What are the subdetectors of the Compact Muon Solenoid experiment? Briefly describe them.

15.

What is the advantage of a colliding-beam accelerator over one that fires particles into a fixed target?

16.

An electron appears in the muon detectors of the CMS. How is this possible?

### 11.5The Standard Model

17.

What is the Standard Model? Express your answer in terms of the four fundamental forces and exchange particles.

18.

Draw a Feynman diagram to represents annihilation of an electron and positron into a photon.

19.

What is the motivation behind grand unification theories?

20.

If a theory is developed that unifies all four forces, will it still be correct to say that the orbit of the Moon is determined by the gravitational force? Explain why.

21.

If the Higgs boson is discovered and found to have mass, will it be considered the ultimate carrier of the weak force? Explain your response.

22.

One of the common decay modes of the $Λ0isΛ0→π−+p.Λ0isΛ0→π−+p.$ Even though only hadrons are involved in this decay, it occurs through the weak nuclear force. How do we know that this decay does not occur through the strong nuclear force?

### 11.6The Big Bang

23.

What is meant by cosmological expansion? Express your answer in terms of a Hubble graph and the red shift of distant starlight.

24.

Describe the balloon analogy for cosmological expansion. Explain why it only appears that we are at the center of expansion of the universe.

25.

Distances to local galaxies are determined by measuring the brightness of stars, called Cepheid variables, that can be observed individually and that have absolute brightnesses at a standard distance that are well known. Explain how the measured brightness would vary with distance, as compared with the absolute brightness.

### 11.7Evolution of the Early Universe

26.

What is meant by a “cosmological model of the early universe?” Briefly describe this model in terms of the four fundamental forces.

27.

Describe two pieces of evidence that support the Big Bang model.

28.

In what sense are we, as Newton once said, “a boy playing on the sea-shore”? Express your answer in terms of the concepts of dark matter and dark energy.

29.

If some unknown cause of redshift—such as light becoming “tired” from traveling long distances through empty space—is discovered, what effect would that have on cosmology?

30.

In the past, many scientists believed the universe to be infinite. However, if the universe is infinite, then any line of sight should eventually fall on a star’s surface and the night sky should be very bright. How is this paradox resolved in modern cosmology?