Particles and Radiation

Question 1

What is a fundamental particle?

Answer 1

A particle which can’t be split into a smaller particle.

Question 2

Why must neutrinos/ antineutrinos exist?

Answer 2

To account for other particles during interactions (e.g. beta decay) having a range of possible energies.

Question 3

State the 2 types of hadrons and their quark compositions.

Answer 3

• Baryons: 3 quarks (have a baryon number)
• Mesons: quark-antiquark pair

Question 4

What are the four fundamental forces, which particles do they affect, and what are their exchange particles?

Answer 4

• Electro-magnetic: affects charged particles; photon (γ)
• Gravity: all particles; graviton (theoretical)
• Weak nuclear: all particles; W⁺, W⁻, Z⁰
• Strong nuclear: hadrons; pion (or gluon)

Question 5

What is the range of the strong force?

Answer 5

• Below 0.5fm – repulsive
• 0.5-3fm – attractive

Question 6

List the 3 strangeness rules.

Answer 6

• If leptons are involved, the interaction is weak
• If only hadrons involved and strangeness is conserved, the interaction is strong (strange particles can be created)
• If strangeness isn’t conserved, the interaction is weak. Strange particles can be destroyed, but total strangeness changes by +/- 1

Question 7

When does annihilation occur and what is its general equation?

Answer 7

A particle and its antiparticle meet. All mass is converted to energy in the form of two photons (to conserve momentum).
2mc² = 2hf
If the particles have kinetic energy, it’s added to the photons’ energies.

Question 8

When does pair production occur, and what is its general equation?

Answer 8

A photon of sufficient energy is converted into a particle and its antiparticle.
hf = 2mc²
If the photon has more than the minimum needed energy, the extra is converted to kinetic energy.

Question 9

What causes electrons to excite?

Answer 9

Colliding with a free electron or absorbing a photon with energy equal to the difference in energy of the levels.

Question 10

What happens when electrons de-excite?

Answer 10

Emits photons with wavelengths depending on the difference in energy levels (ΔE = hf = hc/λ)

Question 11

How can we observe the photoelectric effect?

Answer 11

If light incident on a metal has a high enough frequency, electrons will be liberated from the surface.
Can set up a gap between two surfaces for current to flow through.
Add a variable p.d. to oppose the current until it reaches zero.
Potential needed for this = stopping potential, Vₛ

Question 12

How does light intensity affect photoelectron emission?

Answer 12

Number of photoelectrons emitted per second is directly proportional to intensity of radiation.

Question 13

How does frequency affect photoelectron emission?

Answer 13

The greater the frequency, the greater the kinetic energy.

Question 14

How are emissions and absorption spectrums obtained?

Answer 14

By observing what wavelengths are emitted or absorbed by a gas/ plasma.

Question 15

Outline how fluorescent light tubes work.

Answer 15

• Electrons accelerate from cathode to anode through mercury gas.
• Free electron from cathode excites electron in (low pressure) mercury gas atom.
• When electron de-excites, it emits a UV photon.
• UV photon absorbed by the fluorescent coating which excites an electron
• Electron de-excites by multiple levels, emitting lower frequency visible light photons.

Question 16

What is the difference between the two types of mesons?

Answer 16

Pions are mesons with no strangeness, kaons are mesons with strangeness.