Matter and Radiation

Question 1

What does every atom contain?

Answer 1

A positively charged nucleus composed of protons and neutrons with electrons surrounding the nucleus

Question 2

Define an isotope

Answer 2

Isotopes are atoms with the same number of protons but a different number of neutrons

Question 3

What is the specific charge of a charged particle?

Answer 3

The specific charge of a charged particle is defined as its charge divided by its mass

Question 4

What overcomes the electrostatic force of repulsion between protons in a stable nucleus?

Answer 4

The strong nuclear force

Question 5

What is the range of the strong nuclear force?

Answer 5

No more than 3-4 femtometres (fm) where 1fm = 10⁻¹⁵m

about the diameter of a small nucleus

Question 6

What are the products for the beta- decay of a nucleus X with mass number A and Z number of protons

Answer 6

A nucleus (Y) with mass number A but Z+1 number of protons, an electron (beta⁻ particle) and an antinutrino

Question 7

Give the formula to relate the wavelength of a photon to its frequency

Answer 7

λ = c / f

where c is the speed of light

Question 8

Give the average ranges in wavelength for:

i) infrared spectrum
ii) visible light spectrum
iii) ultraviolet spectrum

Answer 8

i) 1mm - 700nm
ii) 700nm - 400nm
iii) 400nm - 1nm

Question 9

Give the equation for the energy of a photon

Answer 9

E = hf

where h is plank’s constant

Question 10

Describe the relationship between the electric and magnetic field for an electromagnetic wave

Answer 10

They are at 90˚ to each other

Question 11

Describe a laser beam in terms of its photons and give the equation for the power of the beam

Answer 11

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

Question 12

Name the antiparticle for the electron

Answer 12

The positron

Question 13

Give the 3 predictions of Dirac’s theory of antiparticles

Answer 13

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

Question 14

Describe annihilation

Answer 14

Where a particle collides with its antiparticle and annihilates, converting their total mass into two identical photons.

Question 15

Describe pair production

Answer 15

Where a photon of sufficient energy suddenly changes into a particle-antiparticle pair, which separate from each other.

Question 16

Give the equation that states the minimum energy of each photon produced when a particle-antiparticle pair annihilate

Answer 16

hf(min) = E₀

where E₀ is the rest energy of the particle

Question 17

Give the equation to show the minimum energy of photon needed to cause pair production

Answer 17

hf(min) = 2E₀

Where E₀ is the rest energy of the particle

Question 18

What is the electromagnetic force between two charged objects due to?

Answer 18

Virtual photons

Question 19

Why can’t virtual photons be detected

Answer 19

Because if we intercepted them to detect them, we would stop the force between them.

Question 20

What force acts to cause changes in uncharged neutrons into protons or vice versa if the electromagnetic force only acts on charged particles?

Answer 20

The weak nuclear force

Question 21

What does the W- boson decay into in the absence of an antineutrino?

Answer 21

A beta- particle and an antineutrino

Question 22

What does a W+ boson decay into in the absence of a neutrino?

Answer 22

A beta+ particle and a neutrino

Question 23

Describe electron capture

Answer 23

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