# Physics projects for Y3 and Y4 students

## Project description

### Lord Kelvin's Water Drop System for Separating/Storing Charge and Making Sparks!

#### (supervisor: Tony Cook)

Nature of project: experimental, experimental

Available to students on full-time physics degree schemes or joint students.

#### Project description and methodology

Around about 1867 Lord Kelvin demonstrated an experiment, using a source bucket of water with a tap that fed the middle of a horizontal pipe. Half the water went to the left and half to the right. At the ends of the horizontal pipe, the water falls into respective metal buckets on insulated surfaces. As the water falls it passes through a metal ring (not in contact) which is connected to the opposite metal bucket. As the water flows, charge becomes separated and the charge in each metal ring further attracts opposite charge into each underlying bucket. The net result is large charge separation which grows over time. A spark gap is used to demonstrate the amount of accumulated charge. Please check back through your old PH19510 lecture notes for a diagram showing how this works!

Anyway the aim of this project is to optimize the charge separation process by changing some of the experiment physical parameters as discussed in the "Opportunities for Development" section. Activity will be measued by the number of sparks produced in the spark gap per second, by measuring radio interference noise levels, and/or by using a photometer. You will be expected to deduce some relationships and come up with some theories explaining why charge separataion has been increased.

A successful project will develop beyond the above in one/some of the following directions:
Here are some questions which could be answered by experimentation - you might want to consider focussing on one or two of these in detail:

1) what happens if the flow rate is increased?

2) what happens if the rings are closer to the water flow, or larger in surface area?

3) can the efficency be improved by adding soluable chemicals to the water?

When considering where to take your project, please bear in mind the time available. It is preferable to do fewer things well than to try many and not get conclusive results on any of them. However, sometimes it is useful to have a couple of strands of investigation in parallel to work on in case delays occur.

Additional scope or challenge if taken as a Year-4 project: Here are some questions which could be answered by experimentation - you might want to consider focussing on one or two of these in detail

1) What happens if a different liquid is used

2) Or indeed a flow of sand like one has in an egg timer?

3) What happens if the flow is turbulent or contains bubbles?

Please speak to Tony Cook (atc) if you consider doing this project.

Initial literature for students:

1. Thomson, W. (November 1867). The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science. Series 4. 34 (231): 391–396
2. M. Zahn (1973) American Journal of Physics, 41, 196–202.
3. Alvaro G. Marin et al. (2013) Lab Chip, 13, 4503-4506.

#### Novelty, degree of difficulty and amount of assistance required

This is repeating a historic experiment and improving on efficiency of charge separation. One of the difficulties will be charge loss through interaction with the air and how to control or quantify this.

#### Project milestones and deliverables (including timescale)

milestoneto be completed by
Decide what liquids to use, what types of equipment are neededend of October
Decide upon ways to measure the spark energy outputChristmas
Conduct a first set of experiments just using water, but different flow rates or with different concentration of solutionsend of February
Complete some of the suggested variations to the experimentEaster

Students taking this project will have to submit a full risk assessment form