Understanding Electroscope With Simple Experiment


Electroscope is defined as a device that detects electrical charge. Ever imagined, even by suspending pieces of tape from a straw, an electroscope can be built. A simple experiment at home can illustrate electroscope detecting electrical charge. A commonly available plastic tape can gain or lose negatively charged electrons when it is stuck to a surface and then ripped off. A plastic comb enables to identify if that the pieces of tape are either positively or negatively charged.

What are the requirements:

  1. Two plastic film canisters or paper cups
  2. Modelling clay to fill the cans or cups halfway
  3. Four plastic drinking straws with flexible ends
  4. A roll of tape, 3/4-inch (2-cm) width
  5. A plastic comb
  6. Someone with a full head of hair (alternatively, use a piece of wool cloth)

Steps to Assemble

Fill enough quantity of modelling clay into each of the two film canisters or paper cups till halfway to the top. Then press the stubborn ends of two drinking straws into the clay in each canister. Then bend the flexible ends in order to make horizontal arms that extend in opposite directions to each other. It may be noted that the height of both the straws should be at the same level.

How To Execute

First tear off two pieces of the tape, each measuring approx. 4 inches (10 cm) long. Then press each piece firmly to a tabletop or other flat surface, leaving one end of each tape piece sticking up as a handle. Then quickly pluck the tape from the table and stick it to one piece on the arm of a straw in one film canister. Repeat the same procedure to the other piece on the arm of straw placed in another film canister.

Move the canisters in such a position that the two pieces of the tape are face to face with each other, not more than 6 inches (15 cm) apart. Then move both the canisters close to each other. It will be noticed that both the tapes repel each other.

Now, tear two more pieces of tape. Press the sticky side of one tape against the smooth side of the other tape. This leaves one end of each tape piece sticking out as a handle. Now quickly pull off the tape that were stuck together, apart from each other and stick those pieces to the two remaining arms. Now, again bring the arms close to each other and it will be noticed that these two tapes now attract each other.

Just run the comb either through the hair or with the wool cloth, whichever option is selected. And then hold the comb near the hanging tapes. It will be noticed that the comb repels the piece of tape with its smooth side and attracts the tape with its sticky side.

The Results

When the two pieces of tape are ripped off the table, there is a huge conflict of electric charges between tape and table. The tape either steals negative charges i.e., electrons from the table or the tape leaves some of its own negative charges behind, depending on what the table is made of. A point to be considered here is that a positive charge doesn?t move in this situation. In any case, both pieces of tape result in having the same charge, be it positive or negative. And since like charges repel to each other, the pieces of tape here also repel with each other.

When the tape sandwich is pulled apart from each other, one piece gets negative charges from the other one. One piece of tape therefore has some extra negative charges in it. The other piece, which has lost some of the negative charge in the transfer, now has an overall positive charge. And because the opposite charges attract, the two pieces of tape also get attracted to each other.

When a plastic comb is run through the hair, the comb resultingly becomes negatively charged. The tapes repelled by comb now have a negative charge, and tapes attracted by comb either consists of positive charge or are uncharged.

It is the law of science that an uncharged object attracts charged objects. When the hand is held near a positively charged piece of tape, the tape attracts electrons into the body. The part of the body which is nearest to the tape ultimately becomes negatively charged, while a positive charge remains behind on the rest of the body. The positive energy filled tape attracts the nearby negative charges strongly enough, as it is repelled by the more distant positive charges. The tape then moves toward the hand.

Understanding Electroscope

One can use electroscope to test whether an object is electrically charged. Use the comb to determine the kind of charge on a piece of tape, and see whether an object with an unknown charge repels the tape. Note that if the tape is negatively charged and if any object repels with it, then the object is a negatively charged object. Just using attraction to judge if any object is charged or not will not give accurate result. A charged object may even attract any uncharged object. If the tape is attracted to an object, it can either mean that the tape and the object may have opposite charges, or perhaps the tape may be charged and the object uncharged. There is also a possibility that the object may be charged and the tape may be uncharged. But if the tape is repelled by the object, then it means that the tape and the object must have the same charge. The only way that tape and an object will neither repel nor attract to each other is when both of them are uncharged.

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