1.3 Particles - Photons and Antiparticles

Question 1

Photons:

Answer 1

Light could be released in particle-like packets of energy / EM waves, called photons

Question 2

Planck’s constant:

Answer 2

h = 6.63 x 10^-34 J

Question 3

Equation for photon energy:

Answer 3

E=hf or E=hc/wavelength

Question 4

Electronvolt definition:

Answer 4

The work done in a moving electron across a potential difference of 1 volt

Question 5

eV to J:

Answer 5

x 1.60 x10^-19

Question 6

J to eV:

Answer 6

/ 1.60 x10^-19

Question 7

Antimatter:

Answer 7

A particle of equal mass to a particle but of the opposite charge; antiparticle of electron called positron

Question 8

Annihilation:

Answer 8

When a particle meets its own antiparticle, they annihilate each other
This is the process by which the mass of two particles is completely transferred to EM radiation to form 2 equal-energy photons moving in opposite directions

Question 9

Equation for energy of annihilation:

Answer 9

E = mc^2

Question 10

Momentum in annihilation:

Answer 10

Two photons conserve momentum
The total momentum of the electron-positron system is 0 therefore two photons with equal and opposite momenta must he produced to keep system momentum at 0

Question 11

Rest mass:

Answer 11

= mass of body at rest

Question 12

Rest energy:

Answer 12

= energy of body at rest (MeV)

Question 13

Annihilation equation:

Answer 13

E(min) = hf(min) = E

Question 14

Pair production:

Answer 14

When a sufficiently energetic photon passes close to a nucleus, the EM energy of the photon will be converted into particle-antiparticle pair

Question 15

Pair production equation:

Answer 15

E(min) = hf(min) = 2E

Question 16

Why does pair production have to have minimum energy equal to rest masses?

Answer 16

Minimum energy must be equal to the rest mass of the air produced as otherwise surplus energy would appear as kinetic energy carried by the particle and antiparticle