# Credit

This unit is worth 150 UMS, which equates to 50% of the AS credit or 25% of the A2 credit.

# Assessment

It is examined by a single 100-mark 1 hour 45 minute written exam in either January or May/June.

# Content

## Module 1 : Electric current

*This short module introduces the ideas of charge and current. Understanding electric current is essential when dealing with circuits in Modules 2 and 3. This module does not lend itself to practical work but to introducing fundamental ideas. The continuity equation is developed using these fundamental ideas. The module concludes with categorising all materials in terms of their ability to electrically conduct. There are opportunities to discuss how theories and models develop with the history of the electron.*

**Charge and current**

*Candidates should be able to:*

- explain that electric current is a net flow of charged particles;
- 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;
- explain what is meant by conventional current and electron flow;
- select and use the equation ΔQ = IΔt;
- define the coulomb;
- describe how an ammeter may be used to measure the current in a circuit;
- recall and use the elementary charge e = 1.6 × 10-19 C;
- describe Kirchhoff’s first law and appreciate that this is a consequence of conservation of charge;
- state what is meant by the term mean drift velocity of charge carriers;
- select and use the equation I = Anev;
- describe the difference between conductors, semiconductors and insulators in terms of the number density n.

## Module 2 : Resistance

*The aim of this module is to introduce or consolidate the basic concepts required for describing, using and designing electrical circuits. It is vital for a scientist to be able to recall, use and apply scientific vocabulary. Hence, it is important to learn key definitions within this module. Electromotive force and potential difference are defined and distinguished in terms of the energy transferred by charges moving round the circuit. This leads to considering the rate of energy transfer, the power, in each component of the circuit. How current varies with potential difference for a range of components is investigated. The characteristics and uses of light-emitting diodes are also explored. The module closes with an investigation of how the resistivity of metals and semiconductors varies with temperature.*

**Circuit symbols**

*Candidates should be able to:*

- 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);
- interpret and draw circuit diagrams using these symbols.

**E.m.f. and p.d.**

*Candidates should be able to:*

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

**Resistance**

*Candidates should be able to:*

- define resistance;
- select and use the equation for resistance: R = $\frac{V}{I}$;
- define the ohm;
- state and use Ohm’s law;
- describe the I–V characteristics of a resistor at constant temperature, filament lamp and light-emitting diode (LED);
- describe an experiment to obtain the I–V characteristics of a resistor at constant temperature, filament lamp and light-emitting diode (LED);
- describe the uses and benefits of using light-emitting diodes (LEDs).

**Resistivity**

*Candidates should be able to:*

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

**Power**

*Candidates should be able to:*

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

## Module 3 : DC circuits

*The work from Modules 1 and 2 is brought together in this module. At the end of this module, students should have the confidence to connect up circuits and predict the outcome in terms of current or potential difference. To monitor changes in the intensity of light or temperature, passive components are needed like light-dependent resistors and thermistors in electrical circuits. The module explores how this may be done using potential divider circuits. There are opportunities to encourage students to use appropriate scientific vocabulary and make them aware of how data-loggers or computers can be used to monitor physical changes.*

**Series and parallel circuits**

*Candidates should be able to:*

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

**Practical circuits**

*Candidates should be able to:*

- draw a simple potential divider circuit;
- explain how a potential divider circuit can be used to produce a variable p.d.;
- select and use the potential divider equation V
_{out}= R_{2}/ (R_{1}+ R_{2}) x V_{in}; - describe how the resistance of a light-dependent resistor (LDR) depends on the intensity of light;
- describe and explain the use of thermistors and light-dependent resistors in potential divider circuits;
- describe the advantages of using dataloggers to monitor physical changes.

## Module 4 : Waves

*The module begins by reviewing and consolidating students’ prior knowledge about waves and wave properties. This is followed by a short section on electromagnetic waves also reinforcing and amplifying prior knowledge of the electromagnetic spectrum. Students then gain an understanding of superposition effects. The wavelength of light is too small to be measured directly using a ruler; however, experiments can be done in the laboratory to
determine wavelength of visible light using a laser and a double slit. The module concludes by considering stationary waves formed on strings and in pipes. There are opportunities to discuss how theories and models develop with the Young’s double-slit experiment. The dangers of over-exposure to ultraviolet radiation are well known. This module explores which type of ultraviolet radiation is most dangerous to us and illustrates how scientific knowledge can be used to reduce risks for society.*

**Wave motion**

*Candidates should be able to:*

- describe and distinguish between progressive longitudinal and transverse waves;
- define and use the terms displacement, amplitude, wavelength, period, phase difference, frequency and speed of a wave;
- derive from the definitions of speed, frequency and wavelength, the wave equation v = fλ;
- select and use the wave equation v = fλ;
- explain what is meant by reflection, refraction and diffraction of waves such as sound and light.

**Electromagnetic waves**

*Candidates should be able to:*

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

**Interference**

*Candidates should be able to:*

- state and use the principle of superposition of waves;
- apply graphical methods to illustrate the principle of superposition;
- explain the terms interference, coherence, path difference and phase difference;
- state what is meant by constructive interference and destructive interference;
- describe experiments that demonstrate two-source interference using sound, light and microwaves;
- describe constructive interference and destructive interference in terms of path difference and phase difference;
- use the relationships intensity = power/cross-sectional area and intensity ∝ amplitude
^{2}; - describe the Young double-slit experiment and explain how it is a classical confirmation of the wave-nature of light;
- select and use the equation λ = ax/D for electromagnetic waves;
- describe an experiment to determine the wavelength of monochromatic light using a laser and a double slit;
- describe the use of a diffraction grating to determine the wavelength of light (the structure and use of a spectrometer are not required);
- select and use the equation dsinθ = nλ;
- explain the advantages of using multiple slits in an experiment to find the wavelength of light.

**Stationary waves**

*Candidates should be able to:*

- explain the formation of stationary (standing) waves using graphical methods;
- describe the similarities and differences between progressive and stationary waves;
- define the terms nodes and antinodes;
- describe experiments to demonstrate stationary waves using microwaves, stretched strings and air columns;
- determine the standing wave patterns for stretched string and air columns in closed and open pipes;
- use the equation: separation between adjacent nodes (orantinodes) = λ/2;
- define and use the terms fundamental mode of vibration and harmonics;
- determine the speed of sound in air from measurements on stationary waves in a pipe closed at one end.

## Module 5 : Quantum physics

*The aim of this module is to introduce the concept of quantum behaviour. How do we know that light is a wave? The evidence for this comes from diffraction of light. However, this wave-like behaviour cannot explain how light interacts with electrons in a metal. A revolutionary model of light (photon model), developed by Max Planck and Albert Einstein, is needed to describe the interaction of light with matter. Physicists expect symmetry in nature. If light can have a dual nature, then surely particles like the electron must also have a dual nature. We study the ideas developed by de Broglie. The final section looks briefly at the idea that electrons in atoms have discrete bond energies and they move between energy levels by either absorbing or by emitting photons. There are many opportunities to discuss how theories and models develop with the history of wave-particle duality.*

**Energy of a photon**

*Candidates should be able to:*

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

**The photoelectric effect**

*Candidates should be able to:*

- describe and explain the phenomenon of the photoelectric effect;
- 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;
- define and use the terms work function and threshold frequency;
- state that energy is conserved when a photon interacts with an electron;
- select, explain and use Einstein’s photoelectric equation hf = φ + KE
_{max}; - 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.

**Wave–particle duality**

*Candidates should be able to:*

- the wave nature of particles like electrons;
- explain that electrons travelling through polycrystalline graphite will be diffracted by the atoms and the spacing between the atoms;
- select and apply the de Broglie equation λ = h/mv;
- explain that the diffraction of electrons by matter can be used to determine the arrangement of atoms and the size of nuclei.

**Energy levels in atoms**

*Candidates should be able to:*

- explain how spectral lines are evidence for the existence of discrete energy levels in isolated atoms, ie in a gas discharge lamp;
- describe the origin of emission and absorption line spectra;
- use the relationships hf = E
_{1}– E_{2}and hc/λ = E_{1}– E_{2}.

# Past exam papers

G482 | 2010 | 2009 |
---|---|---|

January | Paper Markscheme Report |
N/A |

Summer | Paper Markscheme Report |