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Design Lab, Charge on Balloons

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IB Physics Yr. 2 HL

Design Lab II

IB Design Lab II

Electric Charge in Balloons


To determine the relationship between the volume of a balloon filled with air and the charge on its surface.In this experiment, the given balloons will be filled up with air and then an electroscope will be used to determine the charge on the surface. A wool cloth will be used to charge the balloon of different volumes and then the balloon will be conducted to an electroscope to measure the amount of charge. To determine the volume of the balloon after finding the charge, Archimedes principle will be used. The principle states that when an object is fully or partially immersed in water, the mass of the water displaced is equal to the volume of the object immersed. The mass of water is the same as its volume because the density of water is 1 g cm-3. In this case, the balloon will be immersed in a bucket of water. This bucket will be placed in a big dish so that the water falls in this dish. The mass of this water will then measured using a weighing scale, which then is equal to the volume of the balloon. (Archimedes principle)

Electric charge plays a key role in this experiment.

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 The ways of controlling these variables have been explained in the procedure of this experiment.


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.
  • 1 pair of rubber gloves
  • 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.
  • 1 Weighing scale (±0.1g)
  • 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)
  • 1 Electroscope
  • 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.  
  • 1 Small bucket
  • 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.
  • 1 Dish
  • The water from the bucket will fall into the dish.
  • 1 Beaker (250mL ± 50mL)
  • 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.
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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 dishNow 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

  1. Set up a data table as shown below:

Volume of Balloon (cm3 ± 0.1 cm3)

Angle of repulsion

(° ± 5°)

Data point 1

Data point 2

Data point 3

Data point 4

Data point 5

Data point 6

Data point 7

Data point 8

  1. Repeat steps 1 to 11 with one exception. With every different data point, inflate the balloon more than last time hence having more volume.
  2. 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.
  3. After all values have been measured, keep back all the materials from where they were acquired in the first place.

...read more.

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