Also, the volume of the balloon can only be measured after the charge has been measured. This is because if the balloon is immersed in water before measuring the charge, he balloon will be completely wet and it would be problematic to rub the wool cloth on the wet surface.
There are a number of variables in this experiment. The volume of the balloon will be increased in this investigation, hence being the independent variable. As the volume of the balloon will be varied, the charge will vary accordingly, hence being the dependant variable. Some variables in this experiment have to be controlled in order to get ‘perfect’ results, such variables are:
The electroscope: Different electroscopes have different structures, which might affect the measurement of charge in this experiment.
The size of balloons: The size has to be kept the same since different sizes will stretch differently and hence will have different distribution of charge.
The quality of balloons: Different balloons have different qualities and hence the thickness of balloon can affect the distribution of charge as well.
The wool cloth: The size and type of wool cloth has to be the same since the different wool structure might give different amount of charge to the balloon.
The number of rubbings on the balloons: This is one important variable since the rubbings determine the charge conducted onto the balloons. If one balloon is rubbed more than the other, it will obviously conduct more charge on it and hence defeating the purpose. As a result, the number of rubbings makes it ‘fair’ for the balloons.
Weighing scale: Being a scientific experiment, the units and values have to noted carefully. Changing the measuring device will change the significant numbers.
The ways of controlling these variables have been explained in the procedure of this experiment.
Hypothesis
It can be hypothesized that as the volume of the balloon increases, the charge on the surface decreases. This is because as the volume of the balloon increases, the surface area also increases. As a result, the charge gets distributed all over the balloon instead of just accumulating at one spot. Because the number of rubbings by the wool are controlled, the charge conduced on one balloon would be approximately the same on the other. But the distribution of charge will vary according to the volume or in other words, the surface area.
Materials Required
- Regular Air-Balloons (at least 10)
- These balloons will be used as the independent variable. The balloons will be inflated with carbon dioxide from the investigator’s lungs, then charged and tested.
- 1 Wool Cloth (approx. 10cm x 10cm)
- The wool cloth will be used to charge the balloons through the process of friction. The number of rubbings will be kept constant for all balloons to keep the charge even.
- Rubber gloves are extremely important, as they won’t let the charge pass through them. Having naked hands will earth the balloons, which would defeat the purpose of the experiment. Hence, the rubber gloves are required to keep the charge in the balloon only.
- The weighing scale will be used to measure the mass of water dispersed by the balloon so that the volume of the balloon can be determined (as stated by Archimedes principle)
- The Electroscope will be used to measure the charge on the balloon using conduction. An electroscope that uses the gold-leaf to measure the angle of repulsion would be required.
- The balloons will be immersed into this small bucket (filled to top with water) which will be placed in the dish. The displaced water will fall into the dish from the bucket.
- The water from the bucket will fall into the dish.
- The water from the dish will be transferred into the beaker. This will make it easier for the investigation to measure the mass of water.
Procedure
- After all materials have been acquired as stated under ‘Materials Required’, the investigation can begin.
- Wear the rubber gloves before starting the experiment so that no charge is earthed.
- Take one balloon and fill it with air roughly till it fills up one-third of its limit and tie the balloon with a single knot.
- Use the wool cloth to rub the balloon precisely 10 times only. Rub all over the balloon to distribute the charge evenly. The number of rubbings has to be kept constant so that the charge is distributed evenly and ‘fairly’. (as shown below)
- Now, by using the method of conduction, put the balloon on top of the metal cap of the electroscope and measure the deflection of the gold leaf.
- Fill up the small bucket with water till the top such that the water is not dropping but reaching the rim of the bucket.
- Carefully place this beaker in the dish
- Now fully immerse the balloon in the beaker and let the water fall in the dish. Make sure you do put any finger in the beaker otherwise the values for volume won’t be accurate.
- Now transfer the water from the dish into the beaker (250mL ± 50mL).
- Put this beaker on the weighing scale and measure the mass of water. This value is exactly the same as the volume of the balloon.
- Note down the values of
a. Volume of balloon
b. Angle of repulsion
- Set up a data table as shown below:
- Repeat steps 1 to 11 with one exception. With every different data point, inflate the balloon more than last time hence having more volume.
- Use a different balloon for every data point. In this case, trails would be impossible to do since the same balloon cannot be used again and if a different balloon is used, the volume will always vary.
- After all values have been measured, keep back all the materials from where they were acquired in the first place.
