Notes-for-CAIE

Table of contents

• Quantum Physics
  • State what is meant by work function energy [2]
  • State what is meant by the threshold frequency [2]
  • What is meant by the de Broglie wavelength [2]
  • State the de Broglie relation [2]
  • State what is meant by a photon [3]
  • Describe an experiment to demonstrate the wave nature of electrons [5]
  • State experimental observations that support the particle nature of electromagnetic radiation [3]
  • Explain how the line spectrum of hydrogen provides evidence for the existence of discrete electron energy levels in atoms. [3]
  • Explain why threshold frequency and short emission time provide evidence for the particulate nature of e.m. radiation, as opposed to wave theory [4]
  • Describe the appearance of a visible line emission spectrum [2]
  • Use band theory to explain why the resistance of semiconductor decreases as temperature increases [4]
  • Use band theory to explain why the resistance of copper wire increases as temperature increases [4]
  • Use concept of to explain the existence of the dark lines in emission spectrum of cool gas incident with white light [4]
  • Why a continuous distribution of wavelengths in emission spectrum [3]
  • Why narrow peaks of increased intensity at certain wavelengths in emission spectrum [3]
  • Describe the appearance of the spectrum of the absorption
  • Explain how the energy band is produced
  • Why LDR’s resistance decreases as light intensity increases
• Nuclear Physics
  • Describe the photoelectric effect [2]
  • State what is meant by the binding energy of a nucleus [2]
  • Why binding energy per nucleon of U-235 is smaller than that of La-139 [3]
  • State what is meant by nuclear fission [2]
  • State what is meant by nuclear fusion [1]
  • What is meant by random decay [1]
  • What is meant by spontaneous and random in decay [2]
  • What is meant by radioactive decay [2]
  • Define the decay constant of a radioactive isotope [2]
  • Define radioactive half-life [2]
  • Calculating binding energy [4]
  • Why actual activity not the same with calculated [2]
  • Why kinetic energy of product is less than total energy released [2]
  • Why a nucleus of helium-4 does not spontaneously break down to become nuclei of hydrogen [2]
  • What is meant by mass defect of a nucleus [2]
• Ideal Gases
  • State what is meant by an ideal gas [2]
  • r.m.s. equation [4]
  • What is meant by symbol <c²> [2]
  • State the meaning of the symbol <c²> [1]
  • State two conditions for pV=constant × T to be valid [2]
  • State Avogadro’s constant [2]
  • State what is meant by a mole [2]
  • How molecular movement causes the pressure exerted by a gas [3]
  • State the basic assumptions of the kinetic theory of gases [4]
• Thermal Physics
  • What is meant by internal energy of a system [2]
  • Why absolute scale of temperature differs from other temperature scales [1]
  • What is meant by absolute zero of temperature [1]
  • What is meant by specific latent heat [3]
  • Define specific latent heat [2]
  • Define specific latent heat of fusion [2]
  • Why melting requires energy but there is no change in temperature [3]
  • Two processes for which thermal energy is required during boiling [2]
  • The first law of thermodynamics [3]
  • Observations that show why temperature does not measure the amount of heat [4]

Quantum Physics

State what is meant by work function energy [2]

m20 42 Q10

• Minimum energy of photon required to remove an electron
• … from surface.

State what is meant by the threshold frequency [2]

• Minimum frequency for electron to be emitted
• of electromagnetic radiation.

What is meant by the de Broglie wavelength [2]

• wavelength of wave associated with a particle
• …, that is moving.

State the de Broglie relation [2]

• λ = h / p,
• explain λ, h, p.

State what is meant by a photon [3]

Write all the 3 points.

• Photon is discrete amount of energy
• … of an electromagnetic radiation.
• energy = hf

Describe an experiment to demonstrate the wave nature of electrons [5]

• Electron beam in a vacuum
• incident on carbon film.
• fluorescent screen
• pattern of concentric rings observed
• similar to diffraction pattern observed with visible light

State experimental observations that support the particle nature of electromagnetic radiation [3]

w20 42 Q11 [2]
s17 42 Q10 [2]
s19 42 Q11 [3]

• Maximum k.e. dependent (not proportional) on frequency.
• Maximum k.e. independent of intensity.
• Instantaneous emission pf electrons.
• No emission of electrons below threshold frequency.

Explain how the line spectrum of hydrogen provides evidence for the existence of discrete electron energy levels in atoms. [3]

• Each line represents photon of specific energy.
• Photon emitted s a result of energy change of electron
• Specific energy changes so discrete levels.

Explain why threshold frequency and short emission time provide evidence for the particulate nature of e.m. radiation, as opposed to wave theory [4]

Write all the 5 points.

• For a wave, electron can collect energy continuously.
• Wave theory predicts any frequency would give rise to emission of electron
• … if exposure time is sufficiently long.
• Photon has specific value of energy dependent on frequency.
• Emission if energy greater than threshold energy to remove electron from surface.

Describe the appearance of a visible line emission spectrum [2]

w18 42 Q11

• Mostly dark
• Coloured lines

Use band theory to explain why the resistance of semiconductor decreases as temperature increases [4]

w19 42 Q10 [4]
s19 42 Q7 [5]

Write all of them.

• Electron in valence band gain energy.
• Electrons jump to conduction band.
• Holes are left in the valence band.
• Both holes and electrons act as charge carriers.
• Increased number of charge carriers cause lower resistance.

Use band theory to explain why the resistance of copper wire increases as temperature increases [4]

s20 42 Q11 [4]
m18 42 Q11 [4]

• Conduction band and valence band overlap. / No forbidden band.
• Number of charge carriers does not vary.
• Increase in temperature gives rise to increased lattice vibrations.
• Lattice vibrations hinder movement of charge carriers so resistance increases.

Use concept of to explain the existence of the dark lines in emission spectrum of cool gas incident with white light [4]

s20 43 Q10

• Electron gain energy from photon.
• Energy of photon is equal to difference in energy levels.
• Electron moves to higher energy level.
• Electron de-excites and emits photon
• … in all directions.

Why a continuous distribution of wavelengths in emission spectrum [3]

w20 Q7 [3]

• X-ray photon produced when electron is decelerated.
• Larger acceleration results in larger photon energy.
• Continuous range of accelerations so continuous spectrum of wavelengths.

Why narrow peaks of increased intensity at certain wavelengths in emission spectrum [3]

w20 Q7 [3]

• Electron in target atom is excited.
• Electron de-excites causing emission of a photon.
• Discrete energy levels so discrete photon wavelengths.

Describe the appearance of the spectrum of the absorption

• Electrons in cold gas molecules interact with photons.
• Photon energy causes electrons to move to higher energy level.
• Photon’s energy equals to the difference of energy level.
• Photons re-emitted in all directions.

Explain how the energy band is produced

• Atoms in solids are close together, electrons from one atom interact with those of neighbouring atoms,
• this change their electron energy levels, causing a spread of energy level into a band.

Why LDR’s resistance decreases as light intensity increases

• In darkness, conduction band isempty, so high resistance,
• In daylight, electrons in valence absorb photons, jump into conduction band, leaving holes in valence band
• More charge carriers, so resistance decreases.

Nuclear Physics

Hints

• For calculations involving decay, consider A=λN (not provided) and A=A0 e^(-λt) (provided).

Describe the photoelectric effect [2]

s18 42 Q10

• Emission of electrons
• … when electromagnetic radiation incident on surface.

State what is meant by the binding energy of a nucleus [2]

• Energy required to separate nucleons in a nucleus
• … to infinity.

Why binding energy per nucleon of U-235 is smaller than that of La-139 [3]

s17 42 Q12

• When A > 56, binding energy per nucleon decreases as A increases.
• U-235 has larger nucleon number,
• … so less.

State what is meant by nuclear fission [2]

• Heavy nucleus breaks up
• … into two nuclei of approximately equal mass.

State what is meant by nuclear fusion [1]

• Light nuclei combine t o form heavier nuclei.

What is meant by random decay [1]

w19 42 Q12

• decay is unpredictable

What is meant by spontaneous and random in decay [2]

s20 43 Q12

spontaneous:

• decay is not affected by environment

random:

• time at which a nucleus will decay is not predictable.

What is meant by radioactive decay [2]

s18 42 Q10 [2]
w17 42 Q12 [2]

• Spontaneous emission of particles by unstable nucleus.

Define the decay constant of a radioactive isotope [2]

w19 42 Q12

• Probability of decay of a nucleus
• … per unit time.

Define radioactive half-life [2]

• Time for number of atoms
• … to be reduced to one half

Calculating binding energy [4]

s19 42 Q12 [4]

• Calculate mass defect
• E=mc²

Why actual activity not the same with calculated [2]

s20 43 Q12 [2]

• Additional source of activity.
• Emission from daughter products.

Why kinetic energy of product is less than total energy released [2]

s19 42 Q12 [2]

Po -> Pb + He
KE of He not eq to energy equivalent to mass defect.

• Kinetic energy of recoil of Pb.
• Energy of γ-ray photon.

Why a nucleus of helium-4 does not spontaneously break down to become nuclei of hydrogen [2]

s20 42 Q12

• Amount of energy released in forming hydrogen isotopes
• … is less than energy required to break apart helium nucleus.

or

• Binding energy per nucleon of helium is much greater,
• so would require a large amount of energy to separate nucleons in helium.

What is meant by mass defect of a nucleus [2]

s20 42 Q12

• Difference between mass of nucleus and mass of nucleons where nucleons are separated to infinity.

Ideal Gases

State what is meant by an ideal gas [2]

• Obeys the law pV=nRT
• … at all values of p, V and T.

If [3], write also:

• p - pressure
• V - volume
• T - temperature

r.m.s. equation [4]

s20 42 Q2

p = (1/3)ρ<c²>

Explain how terms are derived:

• ρ: NM/V (from PV=nRT)
• 1/3: molecules move ini 3 directions

What is meant by symbol <c²> [2]

• Mean value of the square
• … of the speeds of the particles.

State the meaning of the symbol <c²> [1]

• mean square speed

State two conditions for pV=constant × T to be valid [2]

• Fixed mass of gas
• Ideal gas

State Avogadro’s constant [2]

• Number of atoms of carbon-12
• … in 0.012 kg of carbon-12.

State what is meant by a mole [2]

• Amount of substance
• … containing same number of particles as in 0.012 kg of carbon-12.

How molecular movement causes the pressure exerted by a gas [3]

m20 42 Q2

• Molecules rebound from wall of vessel.
• Change in momentum gives rise to impulse.
• Forces on molecule so force on wall.
• Many impulses averaged to give constant force.

State the basic assumptions of the kinetic theory of gases [4]

Hint: sphere, volume, random motion, inter-collision, inter-force

• Molecules behave as elastic spheres.
• Volume of molecules is negligible compared to the volume of the containing vessel.
• Molecules are in random motion.
• Time of collision is negligible to time between collisions.
• No forces of attraction or repulsion between molecules.

Thermal Physics

What is meant by internal energy of a system [2]

• sum of potential energy and random kinetic energy of atoms

Why absolute scale of temperature differs from other temperature scales [1]

• it does not depend on the property of a substance

What is meant by absolute zero of temperature [1]

• temperature at which atoms have minimum energy

What is meant by specific latent heat [3]

• thermal energy required to change the state of a substance
• … per unit mass
• … without change in temperature

Define specific latent heat [2]

m17 42 Q2 [2]

• Thermal energy per unit mass required to change state
• … without change in temperature

Define specific latent heat of fusion [2]

w18 42 Q2

• Thermal energy required to convert unit mass of solid to liquid
• … without change in temperature

Why melting requires energy but there is no change in temperature [3]

s18 42 Q1

• On melting, bonds between molecules are broken,
• potential energy increased,
• kinetic energy unchanged so no temperature change.

Two processes for which thermal energy is required during boiling [2]

• increasing separation of molecules
• doing work against atmosphere

The first law of thermodynamics [3]

m17 42 Q2 [2]

△U = q + W

• △U: increase in internal energy
• q: heat supplied to the system
• w: work down on the system

Observations that show why temperature does not measure the amount of heat [4]

• • Two objects of different masses at same temperature
  • … would have different amount of heat
• • When substance melts
  • … heat input but no temperature change
• • Temperature shows direction of heat transfer
  • … from high to low regardless of objects