Matter and Radiation Flashcards
What does every atom contain?
A positively charged nucleus composed of protons and neutrons with electrons surrounding the nucleus
Define an isotope
Isotopes are atoms with the same number of protons but a different number of neutrons
What is the specific charge of a charged particle?
The specific charge of a charged particle is defined as its charge divided by its mass
What overcomes the electrostatic force of repulsion between protons in a stable nucleus?
The strong nuclear force
What is the range of the strong nuclear force?
No more than 3-4 femtometres (fm) where 1fm = 10⁻¹⁵m
about the diameter of a small nucleus
What are the products for the beta- decay of a nucleus X with mass number A and Z number of protons
A nucleus (Y) with mass number A but Z+1 number of protons, an electron (beta⁻ particle) and an antinutrino
Give the formula to relate the wavelength of a photon to its frequency
λ = c / f
where c is the speed of light
Give the average ranges in wavelength for:
i) infrared spectrum
ii) visible light spectrum
iii) ultraviolet spectrum
i) 1mm - 700nm
ii) 700nm - 400nm
iii) 400nm - 1nm
Give the equation for the energy of a photon
E = hf
where h is plank’s constant
Describe the relationship between the electric and magnetic field for an electromagnetic wave
They are at 90˚ to each other
Describe a laser beam in terms of its photons and give the equation for the power of the beam
A laser beam consists of photons of the same frequency.
The power of the beam is the energy per second transferred by the photons. Thus,
Power = nhf
where n is the number of photons passing a fixed point per second
Name the antiparticle for the electron
The positron
Give the 3 predictions of Dirac’s theory of antiparticles
For every particle, there is an antiparticle that:
1) annihilates the particle and itself if they meet, converting their total mass into photons
2) has exactly the same rest mass as the particle
3) has exactly opposite charge to the particle if the has a charge
Describe annihilation
Where a particle collides with its antiparticle and annihilates, converting their total mass into two identical photons.
Describe pair production
Where a photon of sufficient energy suddenly changes into a particle-antiparticle pair, which separate from each other.
Give the equation that states the minimum energy of each photon produced when a particle-antiparticle pair annihilate
hf(min) = E₀
where E₀ is the rest energy of the particle
Give the equation to show the minimum energy of photon needed to cause pair production
hf(min) = 2E₀
Where E₀ is the rest energy of the particle
What is the electromagnetic force between two charged objects due to?
Virtual photons
Why can’t virtual photons be detected
Because if we intercepted them to detect them, we would stop the force between them.
What force acts to cause changes in uncharged neutrons into protons or vice versa if the electromagnetic force only acts on charged particles?
The weak nuclear force
What does the W- boson decay into in the absence of an antineutrino?
A beta- particle and an antineutrino
What does a W+ boson decay into in the absence of a neutrino?
A beta+ particle and a neutrino
Describe electron capture
When a proton in a proton-rich environment interacts with an inner-shell electron by the weak-interaction, the proton forms a neutron and the W+ boson changes the electron into a neutrino
