3.2.1.3 - Particles, Antiparticles and Photons

Question 1

What is a photon?

Answer 1

Packet of electromagnetic waves.

Question 2

The greater the frequency of the radiation…

Answer 2

…the greater the energy of the photon.

Question 3

In E=hf what does h and f mean?

Answer 3

h= Planck’s constant and f= frequency.

Question 4

In E=hf what does f have to be in?

Answer 4

m

Question 5

How do you convert nm into m?

Answer 5

Times by 10^-9

Question 6

In E=hc/λ what does c mean?

Answer 6

c= speed of light

Question 7

What is one electron volt?

Answer 7

The energy change of an electron when it moves through a potential difference of 1 volt.

Question 8

Energy in eV =

Answer 8

Energy of photon / 1.6x10^-19

Question 9

What happens when energy is converted into mass?

Answer 9

iYou get equal amounts of matter and antimatter.

Question 10

By what are electromagnetic waves emitted?

Answer 10

By a charged particles when it loses energy.

Question 11

When are electromagnetic waves emitted?

Answer 11

A fast moving electron is stopped or slows down or changes direction.
An electron in a shell of an atom moves to a different shell of lower energy.

Question 12

What is the antiparticle of a proton?

Answer 12

Antiproton.

Question 13

What is the antiparticle of a neutron?

Answer 13

Antineutron.

Question 14

What is the antiparticle of an electron?

Answer 14

Positron.

Question 15

What is the antiparticle of a neutrino?

Answer 15

Antineutrino.

Question 16

What are the similarities between an antiparticle and corresponding particle?

Answer 16

Antiparticles have the same rest mass as the particle but have the opposite charge.

Question 17

1MeV =

Answer 17

1.6x10^-13J

Question 18

When does annihilation occur?

Answer 18

When a particle and a corresponding antiparticle meet and their mass is converted into energy.

Question 19

Why are two photons produced during annihilation?

Answer 19

Two are produced with equal energies because of conservation of energy.

Question 20

What happens when an electron and positron annihilate?

Answer 20

Their mass is converted into energy and a pair of gamma rays are produced to conserve momentum.

Question 21

Minimum energy of each photon produced in annihilation?

Answer 21

E0

Question 22

What happens in pair production?

Answer 22

A photon creates a corresponding particle and antiparticle, and vanishes in the process.

Question 23

When does pair production occur?

Answer 23

It only happens when one photon has enough energy to produce a mass - only gamma ray photons have enough energy.

Question 24

Why does pair production tend to happen near a nucleus?

Answer 24

It helps conserve momentum.

Question 25

What and why is usually produced in pair production?

Answer 25

Electron-positron pairs because they have a relatively low mass.

Question 26

What is the minimum energy for a photon to undergo pair production equal to?

Answer 26

The total rest energy of the particles produced.

Question 27

Why are the particle tracks curved during pair production?

Answer 27

There's usually a magnetic field present in the experiment. They curve in different direction because of the opposite charges of the electron and positron.

Question 28

Minimum energy of each photon produced in pair production?

Answer 28

2E0

Question 29

What changes occur in a proton rich nucleus when it emits a positron?

Answer 29

Proton turns into a neutron. Positron and a neutrino are created and emitted from the nucleus.

Question 30

Differences between pair production of a positron and an electron from positron emission?

Answer 30

- no photons involved in positron emission. | - no neutrinos are emitted in pair production.