Synopsis

Experiments run in three sessions during Michaelmas (E1a/E1b/E1c) and three during Lent (E2a/E2b/E2c).  Efforts are made to give students maximum choice and flexibility although it is not always feasible to run all the experiments.

Two weeks is allowed for practical work with a further 10 days for writing the report.  Prior to starting experimental work, students will be given a short briefing from the head of class. They are then expected to work independently, and can carry out experimental work any time when the Part II labs are open 09:00-17:45 (09:00-17:15 Wednesday), during the two week period allowed for practical work.

Experimental Reports

The experimental report should usually be presented in the style of a paper published in a scientific journal. The main text (excluding appendices and abstract) should be concise, 3000 words maximum (excluding references and figure captions). The text should describe and explain the main features of the project, the methods used, results, discussion and conclusions, and should be properly referenced. In addition, there must be an abstract of at most 300 words. Students should refer to the handout ‘Keeping Laboratory Notes and Writing Formal Reports’ for further details about writing experimental reports.

Submission of your report

Please upload you report to the TIS. To submit your report, go to the 'My experiments' tab, you will find details on how to submit your work there. You may upload as may copies as you wish up to the deadline. In order to preserve anonymity when your report is looked at by the Part II examiners, your name must not appear on the report itself, but please include the name of the experiment and Head of Class.  

Late Submission of Coursework

The Department of Physics expects students to meet the advertised deadlines for the submission of all coursework, to ensure fairness to all students taking the course and allow prompt marking by the Department. 

In accordance with the University's regulations, work submitted after the advertised deadline will not count towards your final examination mark, unless the Department grants an extension of time on the grounds that there are significant mitigating circumstances.

Any application for such an extension should be made by your college Tutor and Director of Studies to the Undergraduate Office, (undergraduate-office@phy.cam.ac.uk).  Students must complete the form available from the teaching webpages, including supporting cases from Tutor and Director of Studies.

In such circumstances, you should submit the work as soon as possible after the deadline.

Before the end of the relevant term, the report will be assessed by the Head of Class, who will then conduct a viva voce examination (typically 30 minutes long). The student will be asked to give a short verbal summary (typically 10 minutes), normally uninterrupted, of the report during the examination. Students should expect to be contacted by the Head of Class shortly after the submission of their report, to arrange the examination.

These Head of Class will write a report to the Part II Examiners and will recommend a mark. These marks are not necessarily final and may be amended by the examiners, who will also look at the report and the Head of Class’s written assessments. After the viva, you will receive a copy of the mark sheet, which will provide feedback on your performance. The marks allocated by the Head of Class are subject to moderation and scaling by the examiners, so the mark you receive may not match the final mark for this piece of work in the College Markbook.

The following guidelines for allocation of marks to Part II experimental reports will be given to the Head of Class.

• Understanding: (30%): of the physical system being measured, and of the experimental design.
• The experiment (40%): how well the work was done, quality of results, discussion of errors.
• Communications skills 1 - Report (20%): Was the report well written and clearly organised, with clear and well balanced arguments, appropriate use of figures, tables and references.
• Communications skills 2 - Viva (10%): Was the student able to summarise the work and respond coherently to questions?

If there are any queries concerning these arrangements, contact, Helen Marshall in the Undergraduate Office (undergraduate-office@phy.cam.ac.uk).

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Optical Pumping of Rb - Dr Tiffany Harte/Dr Christoph Eigen

Part II Laboratory, Room 169 (4 spaces)

The Zeeman effect in the ground state of the rubidium atom is studied, 

nuclear spins of 85Rb and 87Rb are obtained and multi-photon absorption 

and power broadening are investigated

The objectives of the experiment are:

i) to study the Zeeman effect in the ground state of both isotopes of the rubidium atom

ii) to obtain the nuclear spins of 85Rb  and  87Rb

iii) to make accurate measurements of the ground state Landé splitting factors, g

iv) to investigate (a) multiphoton absorption and (b) power broadening. 

The Rb sample is contained in a small spherical cell and coils provide a B-field which both cancels the earth’s field and produces the Zeeman splitting.  Optical pumping by a separate Rb lamp is using to produce a non-equilibrium population of levels in the Rb atoms in the cell.   Changes in the absorption of the Rb line can then be produced, and detected, resulting from the application of an exciting RF field at a frequency corresponding to the Zeeman splitting.

The experiment will certainly enhance your understanding of atomic physics!

Semiconductor Quantum Devices - Dr Adrian Ioenscu

Part II Laboratory, Room 170 (5 spaces)

The resonant tunnelling of electrons in semiconductors  is investigated at both room temperature and 77K.

The experiment involves measurements of a Resonant Tunnelling Diode (RTD), samples of which are manufactured in the Cavendish.  The device acts as a double quantum barrier, the properties of which are an extension of those of the single barrier (met in IB Quantum) and the Fabry-Perot interferometer (IB Optics).

The experiment is designed to be ‘open-ended’ based on measurements of the current/voltage characteristic of the device at both room temperature and 77 K (liquid N2).   The results are compared with the relevant theory.

Mobility of Carriers in Semiconductors - Dr Akshay Rao

Pt II Laboratory, Room 173  (2 spaces)

Propagation of carriers through a semiconductor is measured by a direct method

The purpose of the experiment is to investigate experimentally fundamental transport processes in semiconductors, including drift, diffusion, recombination as well as injection from metal contacts. A pulse of minority carriers is injected at one end of a bar of germanium.  By measuring the arrival time and the shape of the current pulse at the other end of the bar direct information about the charge transport processes in the semiconductor is obtained.

The measurements required include:

i) Measurement of the mobility of Ge and its temperature dependence

ii) Estimate of the minority carrier lifetime in Ge

iii) Verification of the Einstein relation between mobility and diffusion coefficient

iii) Determination of the current/voltage characteristic of the rectifying injecting point contact. 

Dynamics in Complex Fluids - Dr Diana Fusco

Part II Laboratory, Room 155B (4 spaces)

This experiment has two aims (a) to understand the stochastic motion of passive and driven micron-sized objects, suspended in solution of both Newtonian and viscoelastic fluids; (b) use a fairly new and very powerful method of processing time-lapse video data, called Differential Dynamic Microscopy (DDM).

Brownian motion should be a familiar concept: thermal fluctuations drive the random motion of all molecules and particles in a fluid, and if a small tracer is suspended it will be seen to move diffusively. The mean square displacement grows linearly with time, and the coefficient is well known.  This can be used to measure the properties of the suspended particles (e.g. particle size, if the fluid is characterised), or viceversa to learn about the fluid (viscosity) if the particles are well known.  Very different is the situation of a driven particle: at low Reynolds number, a micron sized particle subject to a constant force quickly reaches a steady velocity, so its mean square displacement grows with the square of time.  A different power law.  A qualitative change can also be seen if particles are suspended in fluids that have some elastic character as well as viscous dissipation: in this case the motion is sub-diffusive, and the mean-square displacement versus time can often again be approximated by a power law, with exponent less than one.  All these cases will be measured during the experiment.  The first week will be quite prescriptive, on Newtonian fluids; week 2 will be open to personal investigations. Some theory can also be derived and deployed to match the data.

The experimental setup is made of very simple equipment (in our prototypes we used spare bits...), and the components of the experiment do not have stringent technical constraints, there is no alignment.  High frame rate video is recorded on the computer.   The DDM analysis consists of a series of spatial Fourier transforms,  applied on every pair of image separated by a give time lag.   The growth (as a function of the lag time) of the amplitudes of these Fourier modes contains all the dynamics in the movie,   resolved (because of the spatial FT) by lengthscale.   So from one movie, one can get characteristic dynamical times for every process at every lengthscale.  This is incredibly powerful, and in contrast to many other image analysis methods does not require any user input (no filter parameters, etc).  

Phase- Locked loops - Professor Pietro Cicuta

Bragg Building, Room 168 (5 spaces)

Operation and optimisation of phase-locked loops is investigated, for frequency locking and for recovery of signals buried in noise, and elements of programming-based computer control and data acquisition are introduced.

The experiment is based around the 4046 CMOS integrated circuit; this is designed for phase-locked loop applications and can be operated in two different modes, depending on the type of (integral) phase comparator which is used. The object of the experiment is to investigate the behaviour of the device in a variety of different applications, using each of the available comparators.

The project involves constructing automated control and measurement systems using the graphical LabVIEW programming environment. Control voltages are applied using an Arduino microcontroller (or otherwise) and experimental parameters are measured using a LabVIEW-linked Picoscope. Investigators will:

• Characterise the properties of the two comparator circuits and of the on-board oscillator using an Arduino as a phase-shifting pulse generator and voltage source.
• Measure the stability and locking/capture ranges of the closed-loop system, using the appropriate degree of automation.
• Assemble and investigate the behaviour of the phase-locked loop in some typical applications – as a frequency multiplier, a demodulator of frequency-modulated signals as a clock regenerator for an irregular train of pulses.

An ability to assemble working circuits and a basic understanding of electronics are helpful assets when doing the experiment. Very basic coding experience will help, though this is not a programming project and will be perfectly accessible to non-experts.

Pulsed NMR at 15 MHz – Dr Andy Irvine

Part II Laboratory, Room 170 (8 spaces)

This experiment investigates and demonstrates the principles of Nuclear Magnetic Resonance (NMR).  Spin-echo methods are employed to study the characteristic NMR properties of a number of samples.

Particle Tracks - Dr Paula Alvarez Cartelle

Bragg Building, Room 178 (5 spaces)

Properties of short-lived hyperons are measured by analysing photographs from a liquid hydrogen bubble chamber

The experiment is based around measurements of film taken from bubble chamber experiments at the CERN particle physics laboratory near Geneva. While this technique is no longer current, it provides an immediate visual, introduction to the subject.

Measurements are made of:

(i) K+  decay modes;

(ii) K- + p interactions. 

For   (ii),  measurements of the decay of  product S+ and S hyperons are made using the projected length of the hyperon track and the curvature of the track of the recoil pion and, in the case of the S+ hyperon the decay mode (via proton or neutron) is noted.   The decays of neutral (.o / S o) hyperons produced in (ii) are also studied.

Quantities which you are asked to measure include:

(i) the masses and mean lives of S+ and S hyperons

(ii) the branching ratios for the decays S+ . p po and S+ . n p+

(iii) the mass and mean life of the .o hyperon.

Scanning Tunnelling Microscopy - Dr David Ward

Pt IB Laboratory, Room 166 (4 spaces)

The growth kinetics of graphite oxidation pits are investigated on atomic length scales

The Scanning Tunnelling Microscope (STM) is an important tool in current research as it is capable of mapping surfaces on an atomic scale.  Its operation makes use of the tunnelling current of electrons between an atomically sharp tip and a surface placed a very short distance (~10 Å) away.

The instrument is interfaced to, and controlled by, a computer which also produces the images. 

In this experiment, the STM is used to examine the surface of a graphite crystal. Measurements are made on different scales in order to become familiar with, and illustrate the potential of, the instrument.  The STM is then used to investigate the nucleation and growth of oxidation pits on the surface of the graphite.

Coherence and information in a fibre interferometer - Dr Tijmen Euser

Part II Laboratory, Room 167 (4 spaces)

In this practical we consider a Mach Zehnder (MZ) interferometer and some quantum-mechanical implications. The pattern observed behind an MZ interferometer shows interference fringes, provided there is no way to determine which arm a photon has passed. Here we will place an optical amplifier along one of the MZ arms. The amplifier increases via stimulated emission the intensity of laser pulses. When coherent photon pulses from a laser pass the arm, they stimulate the emission of identical, coherent photons by the atoms of the amplifier medium.

What is the outcome of this experiment: Does the amplification localize the photons in one arm and is the interference therefore suppressed? Or does the process of stimulated emission not constrain the position of the incoming photons, so that the interference pattern is preserved and even amplified through the contribution of the stimulated emissions?

The aim of the practical is to perform the measurements and to explain the results. Some of the intermediate objectives are:

(i)  To build a Mach-Zehnder interferometer and to characterize the interference patterns obtained for different light sources.
(ii)  To study optical amplification and to understand how the gain and noise of an amplifier are determined by stimulated and spontaneous emission processes.
 (iii) To place an optical amplifier in one arm of a Mach-Zehnder interferometer and to explain the results.
 

Waveguide - Dr Daniel Molnar

Part II Laboratory, Room 170 (4 spaces)

Waveguide propagation of a cm wavelength radio wave is investigated.

The aims of the experiment are:

i) to verify the waveguide propagation formula frequencies both above and below cutoff;

ii) to use standing-wave measurements to determine the impedance of a reactive probe;

iii) to use the probe to match an arbitrary impedance (resistive sheet) at the end of the guide.

A solid-state Gunn oscillator provides a tunable signal in the range 8-11 GHz.  Measurements of the standing-wave are made by means of a (high-impedance) probe in a slotted section of guide.  For part (iii) a Smith chart is used to predict the variation of (normalised0 impedance along the guide and to verify the correct conditions for matching.  (The Smith chart is a convenient, conformally-transformed, plot of the variation of complex inpedance with distance along a waveguide - or transmission line.)