Unit 2 - Particles and Waves

Question 1

What are fundamental particles?

Answer 1

Fundamental particles are not composed of other particles. This means that fundamental particles cannot be ‘broken down’ into smaller particles.

Question 2

What are fermions?

Answer 2

Matter particles (if a particle has mass then it must be a fermion). Quarks and Leptons.

Question 3

What types of leptons are there?

Answer 3

Electrons, muons, tau and 3 neutrinos.

Question 4

What are bosons?

Answer 4

Force mediating particles.
Gluon - strong force
W and Z bosons - weak nuclear force
Graviton - Gravitational force
Photon - Electromagnetic force

Question 5

What are hadrons?

Answer 5

mesons and baryon.

Question 6

What are mesons made of?

Answer 6

One quark and one antiquark.

Question 7

What are baryons made of?

Answer 7

3 quarks OR 3 antiquarks.

Question 8

What is proof of the antineutrino and therefore the neutrino?

Answer 8

Beta decay.

Question 9

What is potential difference of two points in an electric field?

Answer 9

A measure of the work done (W) in moving a coulomb of charge (Q) between the two points.

Question 10

Explain how a cyclotron accelerator works

Answer 10

Ions are injected at a point near the centre. An alternating potential difference between the ‘dee’ shaped electrodes accelerates the particles. A magnetic field causes the particles to move in a circular path. When the particle crosses from one ‘dee’ to another it accelerates. After each acceleration, the particle moves to a slightly larger orbit. When it reaches the outer edge of the cyclotron the particle beam is extracted and used in other experiments.

Question 11

Explain how a linear accelerator (LINAC) works.

Answer 11

Charged particles are accelerated in a vacuum pipe through a series of electrodes by an alternating voltage. The beam of particles is then directed at a target or into a synchrotron.

Question 12

Explain how a synchrotron works.

Answer 12

This is similar to a linear accelerator, bent into a ring so the charged particles can be given more energy each time they go round. Electromagnets keep the particles in a curved path. As the speed increases, the magnetic field strength is increased. As the speed increases and relativistic effect cause the mass of the particles to increase, a larger force is needed to accelerate them and keep them in a circular path.

Question 13

What is meant by the term nuclear fusion?

Answer 13

Two small nuclei combine to form a larger nucleus.

Question 14

Why is energy released in nuclear reactions?

Answer 14

Some mass is lost and converted to energy.

Question 15

Why do you need magnetic fields to contain plasma inside a fusion reactor?

Answer 15

Plasma would cool down if it came too close to the sides OR plasma would melt the sides of the reactor.

Question 16

What is threshold frequency (f₀)?

Answer 16

Threshold frequency is the minimum frequency of a photon required to cause photoemission (an electron to be ejected)

Question 17

What is work functions (hf₀)?

Answer 17

Work function is the minimum energy required to cause photoemission (an electron to be ejected)

Question 18

What is constructive interference?

Answer 18

When waves meet in phase

Question 19

What is destructive interference?

Answer 19

When waves meet exactly (180°) out of phase

Question 20

What is absolute refractive index (n)?

Answer 20

Absolute refractive index of a medium is the ratio of the speed of light in a vacuum to the speed of light in
a medium.

Question 21

What is the critical angle?

Answer 21

Critical angle is the angle of incidence that causes the angle of refraction to be 90°

Question 22

What is irradiance (I)?

Answer 22

Irradiance is the power per unit area (incident on a surface).

Question 23

Describe what 6Wm^-2 means.

Answer 23

If there is an irradiance of 6 W m-2 at a surface, this means that 6 W of power is incident on 1 square metre
of surface.

Question 24

Explain why the photoelectric effect provides evidence for the particle nature of light

Answer 24

Each photon contains a fixed amount of energy. If light was a wave then the photoelectric effect would occur regardless of the frequency of the light, it would just take longer for electrons to absorb the energy required to be ejected.

Question 25

What happens to the remaining energy in not used to eject electrons in photoelectric emission?

Answer 25

It is converted to kinetic energy.

Question 26

Explain the photoelectric effect with a gold leaf electroscope.

Answer 26

A zin plate that’s negatively charged so covered with negative electrons causes the gold leaf to be repelled by the stem. Ultraviolet light is shone onto the plate which has efficient energy to eject electrons (the photons have energy higher than the work function of zinc). Electrons on zinc escape to air and are replaced by electrons from stem and gold leaf, meaning the gold leaf is not reflected from stem so falls. Higher irradiance of ultra-violet means gold leaf falls faster because more ultra-violet photons strike zinc per second.
NOTE
White light doesn’t do anything as energy isn’t high enough. Ultra-violet on tin plate does not fall, higher work function. If electroscope positively-charged, gold leaf does not fall because stem and gold leaf lack electrons so can’t replace electrons emitted from metal plate.

Question 27

What does coherent mean?

Answer 27

When two waves have a constant phase relationship. Also means the two sources have the same frequency and speed.

Question 28

How do you calculate how many lines the grating has if it has 100 liens per millimetre?

Answer 28

100 lines in a mm
= 100 000 in a mm
d = 1/100 000
= 1x10^-5

Question 29

What wavelength is blue green and red?

Answer 29

Blue = 450nm
Green = 550nm
Red = 650nm

Question 30

What is refraction?

Answer 30

Refraction is the changing of speed of light as it passes from one medium to another.

Question 31

When does total internal refraction occur?

Answer 31

When the angle of incidence is greater than the critical angle.

Question 32

What is a point source?

Answer 32

A point source of light emits light evenly in all directions.

Question 33

What is the energy level closest to the nucleus called?

Answer 33

Ground level.

Question 34

What are the energy levels farther from the nucleus called?

Answer 34

Excited energy levels.

Question 35

When does an electron reach the ionisation level?

Answer 35

When it reaches a distance so far away from the nucleus that the electron can escape from the atom. The atom is said to be in an ionisation state.

Question 36

Out of E3, E2, E1 and E0, what two states create the highest and lowest frequency?

Answer 36

Highest frequency (short wavelength) - E3-E0
Lowest frequency (long wavelength) - E3-E2

Question 37

Explain in terms of wave show a maxima is produced.

Answer 37

Waves meet in phase.