# Waves & Particles

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# PH2.1 WAVES

Content

• Progressive waves
• Transverse and longitudinal waves
• Polarisation
• Frequency, wavelength and velocity of waves
• Diffraction
• Interference
• Two-source interference patterns
• Stationary waves

AMPLIFICATION OF CONTENT Candidates should be able to:

2.1 (a) understand that a progressive wave transfers energy or information from a source to a detector without any transfer of matter;

2.1 (b) distinguish between transverse and longitudinal waves,

2.1 (c) describe experiments which demonstrate the polarisation of light and microwaves;

2.1 (d) explain the terms displacement, amplitude, wavelength, frequency, period and velocity of a wave,

2.1 (e) draw and interpret graphs of displacement against time, and displacement against position for transverse waves only,

2.1 (f) recall and use the equation c = fλ,

2.1 (g) be familiar with experiments which demonstrate the diffraction of water waves, sound waves and microwaves, and understand that significant diffraction only occurs when λ is of the order of the dimensions of the obstacle or slit,

2.1 (h) state, explain and use the principle of superposition,

2.1 (i) describe an experimental demonstration of two-source interference for light, appreciating the historical importance of Young's experiment, and be familiar with experiments which demonstrate two source interference for water waves, sound waves and microwaves;

2.1 (j) use the equation λ=ay/D for double-slit interference,

2.1 (k) show an understanding of path difference, phase difference, and coherence,

2.1 (l) state the conditions necessary for two-source interference to be observed, i.e. constant phase difference, vibrations in the same line,

2.1 (m) recall the shape of the intensity pattern from a single slit and its effect on double-slit and diffraction grating patterns,

2.1 (n) use the equation d sin θ = nλ for a diffraction grating,

2.1 (o) give examples of coherent and incoherent sources,

2.1 (p) be familiar with experiments which demonstrate stationary waves, e.g. vibrations of a stretched string and for sound in air,

2.1 (q) state the differences between stationary and progressive waves,

2.1 (r) understand that a stationary wave can be regarded as a superposition of two progressive waves of equal amplitude and frequency, travelling in opposite directions and that the internodal distance is λ/2

# PH2.2 REFRACTION OF LIGHT

Content

• Refraction.
• Wave Model of Refraction
• Optical Fibre CommunicationKINEMATICS=

AMPLIFICATION OF CONTENT Candidates should be able to:

2.2 (a) recall and use Snell's Law of refraction;

2.2 (b) recall and use the equations n1v1=n2v2 and n1sinθ1=n2sinθ2;

2.2 (c) understand how Snell's Law relates to the wave model of light propagation;

2.2 (d) understand the conditions for total internal reflection and derive and use the equation for the critical angle n1sinc=n2;

2.2 (e) apply the concept of total internal reflection to multimode optical fibres;

2.2 (f) appreciate the problem of multi-mode dispersion with optical fibres in terms of limiting the rate of data transfer and transmission distance;

2.2 (g) explain how the introduction of monomode optical fibres has allowed for much greater transmission rates and distances;

2.2 (h) compare optical fibre communications to terrestrial microwave links, satellite links and copper cables for long distance communication.

# PH2.3 PHOTONS

Content

• The photoelectric effect.
• Photons
• The electromagnetic spectrum
• Line emission and line absorption spectra
• X-rays
• Spontaneous and stimulated emission
• Lasers – energy levels and structure
• The semiconductor laser and its uses

AMPLIFICATION OF CONTENT Candidates should be able to:

2.3 (a) describe how the photo-electric effect can be demonstrated

2.3 (b) describe how the maximum kinetic energy, KEmax, of emitted electrons can be measured, using a vacuum photocell;

2.3 (c) sketch a graph of KEmax against frequency of illuminating radiation;

2.3 (d) understand and recall how a photon picture of light leads to Einstein's equation, Ekmax=hf−φ and how this equation correlates with the graph of Ekmax against frequency;

2.3 (e) describe in outline how X-rays are produced in an X-ray tube, and sketch a graph of intensity against wavelength;

2.3 (f) recall the characteristic properties and orders of magnitude of the wavelengths of the radiations in the electromagnetic spectrum;

2.3 (g) calculate typical photon energies for these radiations;

2.3 (h) understand in outline how to produce line emission and line absorption spectra from atoms;

2.3 (i) describe the appearance of such spectra as seen in a diffraction grating;

2.3 (j) understand and use atomic energy level diagrams, together with the photon hypothesis, to explain line emission and line absorption spectra;

2.3 (k) calculate ionisation energies from an energy level diagram;

2.3 (l) understand and explain the process of stimulated emission and how this process leads to light emission that is coherent;

2.3 (m) understand the concept of population inversion (Note: for A level students the condition N2 > N1 will suffice) and explain that population inversion is necessary for a laser to operate;

2.3 (n) understand that population inversion is not (usually) possible with a 2-level energy system;

2.3 (o) understand how population inversion is attained in 3 and 4-level energy systems;

2.3 (p) understand the process of pumping and its purpose;

2.3 (q) recall the structure of a typical laser i.e. an amplifying medium between two mirrors, one of which partially transmits light;

2.3 (r) know the basic structure of a semiconductor diode laser;

2.3 (s) know that laser systems are far less than 1% efficient in general (usually around 0.01% efficient) due to pumping losses but that semiconductor lasers can obtain 70% efficiency and that pumping requires the application of a p.d. of around 3V;

2.3 (t) know the advantages and uses of a semiconductor laser i.e. small, cheap, efficient and used for CDs, DVDs, telecommunication etc.

# PH2.4 MATTER, FORCES AND THE UNIVERSE

Content

• The nuclear atom
• Leptons and Quarks
• Particle interactions
• Conservation Laws

AMPLIFICATION OF CONTENT Candidates should be able to:

2.4 (a) electrons orbiting in discrete orbits, explaining the composition of the nucleus in terms of protons and neutrons and expressing the nuclear and atomic ic structures using the A-Z-X notation

2.4 (b) recall that matter is composed of quarks and leptons – the following information will be available to candidates in examinations: Lepton and Quark Table [N.B. No questions will be set involving generations higher than generation 1.]

2.4 (c) recall that antiparticles exist to the particles given in the table above,that the properties of an antiparticle are identical to that of its corresponding particle apart from having opposite charge, and that particles and antiparticles annihilate; use the above table to give the symbols of the antiparticles;

2.4 (d) recall the following information about the four forces or interactions,which are experienced by particles: Forces Interaction Table

2.4 (e) recall that quarks are never observed in solation, but bound into composite particles called hadrons, which are classified as either baryons (e.g. the proton or neutron) which consist of 3 quarks or mesons (e.g. pions) which consist of a quark-antiquark pair;

2.4 (f) use tables of data to sugest the quark structure of given baryons or mesons;

2.4 (g) understand that, in particle interactions, charge and lepton number are conserved;

# PH2.5 USING RADIATION TO INVESTIGATE STARS

CONTENT Black-body radiation

• Wien's displacement law – stellar temperatures
• Stefan's law and stellar luminosity
• Intensity and the inverse square law
• Fraunhofer lines and stellar composition

AMPLIFICATION OF CONTENT Candidates should be able to:

2.5 (a) recall that a stellar spectrum consist of a continuous emission spectrum, from the dense gas of the surface of the star, and a line absorption spectrum arising from the passage of the emitted electromagnetic radiation through the tenuous atmosphere of the star,

2.5 (b) recall that bodies which absorb all incident radiation are known as black bodies and that stars are very good approximations to black bodies,

2.5 (c) recall the shape of the black body spectrum and that the peak wavelength is inversely proportional to the absolute temperature (defined by T/K = θ/°C + 273.15) – Wien's displacement law;

2.5 (d) use Wien's displacement law, Stefan's Law and the inverse square law to investigate the properties of stars – luminosity, size, temperature and distance [N.B. stellar brightness in magnitudes will not be required];

2.5 (e) interpret data on stellar line spectra to identify elements present in stellar atmospheres;

2.5 (f) recall that the analysis of stellar spectra reveals that roughly 75% ofthe universe, by mass, is Hydrogen and 24% Helium, with very small quantities of the other elements;

2.5 (g) recall the main branch of the proton-proton chain, which is th e main energy production mechanism in stars like the Sun:

p + p --> d + e^+ + ve ( where d = deuteron Hydrogen-2)

p + d --> Helium-3 + γ ( where γ = photon)

Helium-3 + Helium-3 -->Helium-4 + p + p

and that neutrinos from the first step of this chain can be detected on Earth;

There is a test for PH2.4-2.5 here