Particles and radiation flashcards

Particles and radiation covers the fundamental building blocks of matter and the forces that govern them. Students must understand the quark model of hadrons, the role of leptons, and how antiparticles relate to their matter counterparts. The four fundamental forces are examined, with particular focus on the exchange particles that carry them, especially the W bosons in beta decay. Conservation laws for charge, baryon number, lepton number and strangeness must be applied to particle interactions. Electromagnetic radiation is treated as photons with energy E = hf, and students should understand how pair production and annihilation link matter and energy. The photoelectric effect and electron energy levels in atoms complete the topic, linking quantum ideas to observable phenomena.

1. Card 1

   What is a hadron and how does it differ from a lepton?

   A hadron is a particle made of quarks and feels the strong force. A lepton is a fundamental particle that does not feel the strong force.

2. Card 2

   State the quark composition of a proton and a neutron.

   A proton contains two up quarks and one down quark (uud). A neutron contains one up quark and two down quarks (udd).

3. Card 3

   What is an antiparticle?

   An antiparticle has the same mass as its corresponding particle but opposite charge, baryon number and lepton number. For example, the positron is the antiparticle of the electron.

4. Card 4

   What happens during pair production?

   A high-energy photon converts into a particle and its antiparticle. The photon energy must be at least equal to the total rest mass energy of the pair produced.

5. Card 5

   What exchange particle carries the weak nuclear force in beta-minus decay?

   The W minus boson is the exchange particle. A neutron emits a W minus, which then decays into an electron and an electron antineutrino.

6. Card 6

   State the equation for the energy of a photon.

   E = hf, where E is photon energy in joules, h is the Planck constant (6.63 x 10^-34 J s), and f is the frequency of the electromagnetic radiation.

7. Card 7

   What is the photoelectric effect?

   The photoelectric effect is the emission of electrons from a metal surface when light above the threshold frequency shines on it, showing light behaves as photons.

8. Card 8

   Define the work function of a metal.

   The work function is the minimum energy needed to release an electron from the surface of a metal. It equals hf0, where f0 is the threshold frequency.

9. Card 9

   What is strangeness and when is it conserved?

   Strangeness is a quantum number carried by strange quarks (s = -1 each). It is conserved in strong interactions but can change by 1 in weak interactions.

10. Card 10

    What are the two categories of hadrons?

    Hadrons are divided into baryons (three quarks, e.g. proton) and mesons (one quark and one antiquark, e.g. pion). Both feel the strong nuclear force.

11. Card 11

    What is the baryon number of a quark and an antiquark?

    Each quark has a baryon number of +1/3 and each antiquark has a baryon number of -1/3, so a proton or neutron (three quarks) has baryon number +1.

12. Card 12

    How does electron-volt relate to the joule?

    One electron-volt (eV) is the energy gained by an electron moving through a potential difference of 1 V. 1 eV = 1.6 x 10^-19 J, a useful unit for particle energies.

• Students often think intensity of light controls whether the photoelectric effect occurs, but it is frequency that determines this.
• A common error is forgetting that strangeness can change in weak interactions, leading to wrong conclusions about whether a decay is possible.
• Many students confuse baryon number with mass number; baryon number is a conserved quantum number, not simply the count of nucleons.

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