To get a deflection of the liquid the liquid must be charged and have a dipole or a dipole moment. This happens when the structure of the molecule is asymmetrical demonstrates by the simple molecule water (H2O) which has a dipole. These dipoles will interact with the charged rod and depending on the dipole and charge on rod the liquid will be either pulled closer to the rod or pushed away.
Hypothesis:
The amount that the liquid is deflected will be directly proportional to the square of the distance between the end of the charged rod and the flow of the liquid. Therefore the deflection when the rod is 4cm from the flow will be one quarter of that if the rod is only 2cm away.
Dependant, Independent and Controlled Variables:
The experiment contains elements of all three variables like all other experiments. The dependant variables rely on the independent variable of which the experiment needs at least five for a pattern to be identified. The independent variable within the experiment is the distance between the charged rod and the flow of liquid. These distances should range from 1cm to a larger figure. This figure will rely on whether the deflection of liquid can be detected and even though the force can never reach zero due to the equation the force can become undetectable, and any distance larger than this are not useful for the experiment. Changing the distance in equal proportions will help to identify any pattern that occurs. The dependant variable is the amount of angle of deflection of the liquid. The controlled variables will be the rate of flow of the liquid, as if this is different the deflection will change. The rate of flow of the liquid should be small enough so it is not dripping and the deflection is not too large, but not so large that no deflection can be detected for greater distances. The type of liquid used, in this case water. The charged rod that is being used. The charge on that rod, therefore if being used by rubbing use the same number of rubs. The laboratory in which the experiment is carried out should have no drafts that will affect the deflection of the liquid.
Materials:
- A tap in which a constant stream of water can be produced
- 30cm ruler
- Protractor
- Charged rod
Method:
- Set up the tap so that a steady and constant flow of water can be obtained
- If rubbing a piece of Perspex with a cloth make sure the same amount of strokes is done in the same time and direction
- Let a small and constant amount of water flow from the tap and place the charged rod 1cm away from the flow and use the protractor to determine the angle that the water has been deflected from the norm
- This should be repeated a minimum of three times, until the results are consistent
- The rod should then be placed a maximum distance away from the water in which the deflection is still observable, this will then be the maximum point and use the protractor to measure the angle
- Once consistent results are found for the maximum point, results should be found between the maximum and minimum points
- The rod should be placed in at least three different places to obtain an overall of five or more average deflection data
- These results should then be tabulated and graphed to see if there is a relationship between distance and angle of deflection
Table 1: Example data table, Data obtained directly from experiment distance changes.
Add uncertainties to table for each specific instrument.
Safety Considerations:
There are no major safety considerations other then, abiding by standard laboratory rules and ensuring not so much heat is caused when rubbing the rod to charge it, that it causes a burn.
Bibliography:
Kerr, Gregg. Physics. Melton: IBID, 2008 pp. 156
