G482: Electrons, Waves and Photons

Mr Cowen’s definitive definitions for Electrons, Waves and Photons


Past paper video walkthroughs

OCR Electrons, Waves and Photons June 2013


Past paper walkthroughs

Electrons, Waves and Photons June 2012

Revision videos

Module 1: Electric current

2.1.1 Electric current
(a) explain that electric current is a net flow of charged particles;
(b) explain that electric current in a metal is due to the movement of electrons, whereas in an electrolyte the current is due to the movement of ions;
(c) explain what is meant by conventional current and electron flow;
(d) select and use the equation \Delta Q = I \Delta t;
(e) define the coulomb;
(f) describe how an ammeter may be used to measure the current in a circuit;
(g) recall and use the elementary charge e = 1.6 \times 10^{-19} \mbox{C};
(h) describe Kirchhoff’s first law and appreciate that this is a consequence of conservation of charge;
(i) state what is meant by the term mean drift velocity of charge carriers;
(j) select and use the equation I = Anev;
(k) describe the difference between conductors, semiconductors and insulators in terms of the number density n.


Module 2: Resistance

2.2.1 Circuit symbols
(a) recall and use appropriate circuit symbols as set out in SI Units, Signs, Symbols and Abbreviations (ASE, 1981) and Signs,
Symbols and Systematics (ASE, 1995);
(b) interpret and draw circuit diagrams using these symbols.

2.2.2 E.m.f. and p.d.
(a) define potential difference (p.d.);
(b) select and use the equation W = VQ;
(c) define the volt;
(d) describe how a voltmeter may be used to determine the p.d. across a component;
(e) define electromotive force (e.m.f.) of a source such as a cell or a power supply;
(f) describe the difference between e.m.f. and p.d. in terms of energy transfer.

2.2.3 Resistance
(a) define resistance;
(b) select and use the equation for resistance

R=\frac{V}{I} ;

(c) define the ohm;
(d) state and use Ohm’s law;
(e) describe the I–V characteristics of a resistor at constant temperature, filament lamp and light-emitting diode (LED);
(f) describe an experiment to obtain the I–V characteristics of a resistor at constant temperature, filament lamp and light-emitting
diode (LED);
(g) describe the uses and benefits of using light emitting diodes (LEDs).

2.2.4 Resistivity
(a) define resistivity of a material;
(b) select and use the equation R= \frac{\rho L}{A} ;
(c) describe how the resistivities of metals and semiconductors are affected by temperature;
(d) describe how the resistance of a pure metal wire and of a negative temperature coefficient (NTC) thermistor is affected by temperature.

2.2.5 Power
(a) describe power as the rate of energy transfer;
(b) select and use power equations P = VI, P = I^{2}R, P = \frac{V^{2}}{R} ;
(c) explain how a fuse works as a safety device (HSW 6a);
(d) determine the correct fuse for an electrical device;
(e) select and use the equation W = IVt;
(f) define the kilowatt-hour (kW h) as a unit of energy;
(g) calculate energy in kW h and the cost of this energy when solving problems (HSW 6a).


Module 3: DC circuits

2.3.1 Series and parallel circuits
(a) state Kirchhoff’s second law and appreciate that this is a consequence of conservation of energy;
(b) apply Kirchhoff’s first and second laws to circuits;
(c) select and use the equation for the total resistance of two or more resistors in series;
(d) select and use the equation for the total resistance of two or more resistors in parallel;
(e) solve circuit problems involving series and parallel circuits with one or more sources of e.m.f.;
(f) explain that all sources of e.m.f. have an internal resistance;
(g) explain the meaning of the term terminal p.d.;
(h) select and use the equations \mbox{e.m.f.} = I (R + r) and \mbox{e.m.f.} = V + Ir .

2.3.2 Practical circuits
(a) draw a simple potential divider circuit;
(b) explain how a potential divider circuit can be used to produce a variable p.d.;
(c) select and use the potential divider equation

V_{\mbox{out}} = \frac{R_{2}}{R_{1}+R_{2}} \times V_{\mbox{in}};
(d) describe how the resistance of a light dependent resistor (LDR) depends on the intensity of light;
(e) describe and explain the use of thermistors and light-dependent resistors in potential divider circuits;
(f) describe the advantages of using data loggers to monitor physical changes (HSW 3).


Module 4: Waves

2.4.1 Wave motion
(a) describe and distinguish between progressive longitudinal and transverse waves;
(b) define and use the terms displacementamplitude, wavelength, period, phase difference, frequency and speed of a wave;
(c) derive from the definitions of speed, frequency and wavelength, the wave equation v = f \lambda;
(d) select and use the wave equation v = f \lambda;
(e) explain what is meant by reflection, refraction and diffraction of waves such as sound and light.

2.4.2 Electromagnetic waves
(a) state typical values for the wavelengths of the different regions of the electromagnetic spectrum from radio waves to γ-rays;
(b) state that all electromagnetic waves travel at the same speed in a vacuum;
(c) describe differences and similarities between different regions of the electromagnetic spectrum;
(d) describe some of the practical uses of electromagnetic waves;
(e) describe the characteristics and dangers of UV-A, UV-B and UV-C radiations and explain the role of sunscreen (HSW 6a);
(f) explain what is meant by plane polarised waves and understand the polarisation of electromagnetic waves;
(g) explain that polarisation is a phenomenon associated with transverse waves only;
(h) state that light is partially polarised on reflection;
(i) recall and apply Malus’s law for transmitted intensity of light from a polarising filter.

2.4.3 Interference
(a) state and use the principle of superposition of waves;
(b) apply graphical methods to illustrate the principle of superposition;
(c) explain the terms interference, coherence, path difference and phase difference;
(d) state what is meant by constructive interference and destructive interference;
(e) describe experiments that demonstrate two source interference using sound, light and microwaves;
(f) describe constructive interference and destructive interference in terms of path difference and phase difference;
(g) use the relationships

\mbox{intensity} = \frac{\mbox{power}}{\mbox{cross-sectional area}}

\mbox{intensity} \propto \mbox{amplitude}^{2} ;

(h) describe the Young double-slit experiment and explain how it is a classical confirmation of the wave-nature of light (HSW 1);
(i) Select and use the equation \lambda = \frac{ax}{d} for electromagnetic waves;
(j) describe an experiment to determine the wavelength of monochromatic light using a laser and a double slit (HSW 1);
(k) describe the use of a diffraction grating to determine the wavelength of light (the structure and use of a spectrometer are not
(l) select and use the equation d\sin\theta = n \lambda;
(m) explain the advantages of using multiple slits in an experiment to find the wavelength of light.

2.4.4 Stationary waves
(a) explain the formation of stationary (standing) waves using graphical methods;
(b) describe the similarities and differences between progressive and stationary waves;
(c) define the terms nodes and antinodes;
(d) describe experiments to demonstrate stationary waves using microwaves, stretched strings and air columns;
(e) determine the standing wave patterns for stretched string and air columns in closed and open pipes;
(f) use the equation:

\mbox{separation between adjacent nodes (or antinodes)} = \frac{\lambda}{2};

(g) define and use the terms fundamental mode of vibration and harmonics;
(h) determine the speed of sound in air from measurements on stationary waves in a pipe closed at one end.


Module 5: Quantum physics

2.5.1 Energy of a photon
(a) describe the particulate nature (photon model) of electromagnetic radiation;
(b) state that a photon is a quantum of energy of electromagnetic radiation;
(c) select and use the equations for the energy of a photon: E = hf and E = \frac{fc}{\lambda}
(d) define and use the electronvolt (eV) as a unit of energy;
(e) use the transfer equation eV = \frac{1}{2}mv^2 for electrons and other charged particles;
(f) describe an experiment using LEDs to estimate the Planck constant h using the equation eV = \frac{hc}{\lambda} (no knowledge of semiconductor theory is expected).

2.5.2 The photoelectric effect
(a) describe and explain the phenomenon of the photoelectric effect;
(b) explain that the photoelectric effect provides evidence for a particulate nature of electromagnetic radiation while phenomena
such as interference and diffraction provide evidence for a wave nature;
(c) define and use the terms work function and threshold frequency;
(d) state that energy is conserved when a photon interacts with an electron;
(e) select, explain and use Einstein’s photoelectric equation hf = \phi + \mbox{KE}_{\mbox{max}};
(f) explain why the maximum kinetic energy of the electrons is independent of intensity and why the photoelectric current in a photocell circuit is proportional to intensity of the incident radiation.

2.5.3 Wave-particle duality
(a) explain electron diffraction as evidence for the wave nature of particles like electrons;
(b) explain that electrons travelling through polycrystalline graphite will be diffracted by the atoms and the spacing between the atoms;
(c) select and apply the de Broglie equation \lambda = \frac{h}{mv} ;
(d) explain that the diffraction of electrons by matter can be used to determine the arrangement of atoms and the size of nuclei.

2.5.4 Energy levels in atoms
(a) explain how spectral lines are evidence for the existence of discrete energy levels in isolated atoms, ie in a gas discharge lamp;
(b) describe the origin of emission and absorption line spectra;
(c) use the relationships hf = E_{1} - E_{2} and \frac{hc}{\lambda} = E_{1} - E_{2}.