Particles and Radiation Questions

Question 1

Explain why the emitted electrons from the photoeletric effect have a range of kinetic energies up to a maximum value. (3)

Answer 1

energy of photon is constant/fixed OR energy given to electron is fixed

energy required for electron to leave/escape/emit from the surface/metal OR electron has to overcome work function

maximum kinetic energy is the energy of photon minus the work function

deeper electrons require energy to get to the surface OR have less Ek than surface electrons

Question 2

Descibe the identifying features of the weak force (2)

Answer 2

• acts on both Hadrons and Leptons
• doesn’t conserve strangeness
• it can change quark structure

Question 3

Explain the difference between excitation and ionisation (3)

Answer 3

in either case an electron receives (exactly the right amount of) energy

excitation promotes an (orbital) electron to a higher energy/up a level

ionisation occurs (when an electron receives enough energy) to leave the atom

Question 4

An atom can also become excited by the absorption of photons. Explain why only photons of certain frequencies cause excitation in a particular atom. (4)

Answer 4

electrons occupy discrete energy levels

and need to absorb an exact amount of/enough energy to move to a higher level

photons need to have certain frequency to provide this energy or e = hf

energy required is the same for a particular atom or have different energy levels

all energy of photon absorbed

in 1 to 1 interaction or clear a/the photon and an/the electron

Question 5

A PD is applied across a fluorescent tube with mercury atoms, describe how the atoms are excited. (3)

Answer 5

• electrons accelerated towards anode
• collide elastically with mercury atoms and transfer energy to the atom
• the electrons go up in energy level

Question 6

What is the lepton number of an electron(e^-) and muon(µ^-)? (2)

Answer 6

• electron : +1 Le
• muon: +1 Lµ