Question 1

If a new force were discovered that had a range on the order of 10^-18 meters: (a) predict the mass of the exchange particle. (b) how long is conservation of energy violated in the exchange of this particle?

Accepted Answer

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Question 2

Is the following decay permissible? Σ⁺ → Λ° + π⁺

Accepted Answer

The answer of Is the following decay permissible? Σ⁺ →...

Question 3

Consider a particle composed of quarks.
(a) The negative pion is composed of what combination of up and down quarks?
(b) Is the negative pion a baryon or meson?
(c) Is the negative pion a lepton or a hadron?

Accepted Answer

The answer of Consider a particle composed of quarks.
(a) The...

Question 4

The voltage across the dees of a cyclotron is 30,000 V. How many revolutions do the protons go through in reaching 21 MeV kinetic energy?

Accepted Answer

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Question 5

A cyclotron of radius 0.25 m accelerates protons in a 1.7-T magnetic field. What is the frequency for the applied alternating voltage?

Accepted Answer

The cyclotron frequency is given by the formula f = (qB)/(2πm), where q is the charge of the proton, B is the magnetic field, and m is the mass of the proton. Substituting the known values (q = 1.6 x 10^-19 C, B = 1.7 T, m = 1.67 x 10^-27 kg), we find f ≈ 26 MHz.

Question 6

What is the wavelength of a 20-GeV alpha particle?

Accepted Answer

The wavelength of a particle can be calculated using the de Broglie wavelength formula: λ = h/p, where h is Planck's constant and p is the momentum. For a 20-GeV alpha particle, the momentum is high, leading to a very small wavelength. Calculating this gives approximately 0.063 fm.

Question 7

If electrons are accelerated from rest in a 30 MeV tandem Van de Graaff Accelerator, what is their final kinetic energy?

Accepted Answer

The final kinetic energy of the electrons is equal to the energy provided by the accelerator, which is 30 MeV.

Question 8

A significant step in "unifying" the forces of nature was the discovery that two of the so-called fundamental forces were two parts of a single force. The two forces that were so unified were

Accepted Answer

The unification of the electromagnetic force and the weak force into the electroweak force was a significant achievement in physics, recognized by the Nobel Prize in Physics in 1979.

Question 9

Scientists hope that some day they will be able to produce a theory which will combine the strong force, the weak nuclear force, and electromagnetism. This theory has been called

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Question 10

A deuteron has the same charge as a proton but approximately twice the proton mass. Suppose deuterons are being accelerated in a cyclotron in an orbit of radius 75 cm at a frequency of 8.0 MHz. What magnetic field is needed?

Accepted Answer

The answer of A deuteron has the same charge as...

Question 11

The color charge of leptons is

Accepted Answer

Leptons do not carry color charge; they are not affected by the strong force, which is mediated by color charge in quantum chromodynamics.

Question 12

An electron undergoes a collision with a proton. In the center of mass system, the energy of the electron is 4000 MeV. What is the energy of the electron in the lab system, where the proton is at rest before the collision?

Accepted Answer

The correct answer is A because the energy of the electron in the lab system is given by the following equation:$$E_{lab} = \frac{E_{CM}}{\sqrt{1 - \frac{v^2}{c^2}}}$$where $E_{CM}$ is the energy of the electron in the center of mass system, $v$ is the velocity of the electron in the lab system, and $c$ is the speed of light.In this case, $E_{CM} = 4000$ MeV and $v = 0.99999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999

Question 13

When a positronium atom (electron + positron) decays, it emits two photons. What are the energies of the photons?

Accepted Answer

The total energy of the positronium atom is the sum of the rest mass energies of the electron and positron, each 0.511 MeV. When it decays, it emits two photons, each with energy equal to the rest mass energy of the electron or positron, which is 0.511 MeV.

Question 14

The Large Hadron Collider is expected to produce protons with kinetic energy 7 TeV. What is the speed of these protons?

Accepted Answer

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Question 15

An electron with an energy of 20 GeV (3.20 × 10^-⁹ J) moving in the +x direction collides head on with a stationary proton. After the collision, the electron travels in the -x direction. What is the momentum of the electron after the collision? Note that this is an ultrarelativistic collision so that the energy of the moving masses can be approximated by the expression E ≈ pc. The mass of a proton is 1.67 × 10^-²⁷ kg and that of an electron is 9.11 × 10^-³¹kg.

Accepted Answer

The correct answer is A.The momentum of the electron after the collision is equal to the momentum of the electron before the collision but in the opposite direction. The momentum of the electron before the collision is:$$p = \frac{E}{c} = \frac{20 	ext{ GeV}}{3 	imes 10^8 	ext{ m/s}} = 6.67 	imes 10^{-19} 	ext{ kg m/s}$$Therefore, the momentum of the electron after the collision is:$$p = -6.67 	imes 10^{-19} 	ext{ kg m/s} = -2.5 	imes 10^{-19} 	ext{ kg m/s}$$

Question 16

What is the wavelength of a 2.0-GeV electron?

Accepted Answer

The answer of What is the wavelength of a 2.0-GeV...

Question 17

A cyclotron of radius 0.25 m accelerates protons in a 1.7-T magnetic field. What is the kinetic energy of the protons when they leave the cyclotron?

Accepted Answer

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Question 18

A cyclotron operates at 10 MHz. What magnetic field is needed to accelerate protons?

Accepted Answer

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Question 19

Suppose you were to try to create a proton-antiproton pair by annihilation of a very high energy photon. The proton and the anti-proton have the same masses, but opposite charges. What energy photon would be required?

Accepted Answer

The energy required to create a proton-antiproton pair is at least twice the rest mass energy of a proton. The rest mass energy of a proton is approximately 940 MeV, so the photon must have at least 2 * 940 MeV = 1880 MeV of energy.

Question 20

A cyclotron is designed with a magnet that produces 1.2 T. When refurbished, the magnet is replaced by one that produces 1.5 T. How does the kinetic energy developed by the protons change compared to the previous energy developed?

Accepted Answer

The kinetic energy of a charged particle in a cyclotron is proportional to the square of the magnetic field. Therefore, when the magnetic field is increased from 1.2 T to 1.5 T, the kinetic energy will increase by a factor of (1.5/1.2)^2 = 1.56, or 56%.

Quiz 43: Elementary Particle

If a new force were discovered that had a range on the order of 10-18 meters: (a) predict the mass of the exchange particle. (b) how long is conservation of energy violated in the exchange of this particle?

Is the following decay permissible? Σ+ → Λ° + π+

Consider a particle composed of quarks. (a) The negative pion is composed of what combination of up and down quarks? (b) Is the negative pion a baryon or meson? (c) Is the negative pion a lepton or a hadron?