हिंदी
Maharashtra State BoardSSC (English Medium) 7th Standard
पाठ्यपुस्तक उत्तर८३५५
अवधारणा स्पष्टीकरण और वीडियो३०१
पाठ्यक्रम

Frictional Electricity

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Topics

  • Introduction
  • Experiment 1
  • Experiment 2
  • Experiment 3

Introduction:

When two objects are rubbed against each other, they get charged because of friction. The electric charge produced by this rubbing is called frictional electricity. Rubbing transfers negative charges (electrons) from one object to another. The object that gains electrons becomes negatively charged, and the object that loses electrons becomes positively charged. This charge stays on the object’s surface and does not move, so it is called static electricity.

  • Static electricity stays on the object only for a short time.
  • The charge disappears quickly in moist air, as moisture absorbs it.
  • These experiments work best in dry weather, especially during winter, because moisture in the air reduces the effect of static electricity.

Experiment 1

1. Aim: To observe how objects (straws) behave when charged by rubbing them with a woollen cloth.

2. Requirements: A few plastic straws, woollen cloth (socks or gloves), and glass bottle

3. Procedure

  • Place a straw on a bottle and bring another straw near it. Observe.
  • Rub one straw with a woollen cloth and bring it near the straw on the bottle. Observe.
  • Rub two straws with the woollen cloth. Place one on the bottle and bring the other near it. Observe if they attract or repel.
  • Bring the woollen cloth near the straw on the bottle and observe what happens.

4. Conclusion: Rubbing straws with a woollen cloth creates electric charges. Two charged straws repel each other because they have the same charge, while an uncharged straw may be attracted to a charged one. This experiment shows that friction generates static electricity, causing attraction or repulsion.

Electrically charged objects attract uncharged objects. There is repulsion between electric charges. There is an attraction between them, unlike electric charges. Hence, repulsion is used to identify an electrically charged object.

Changes in the straw

Procedure Repulsion or Attraction Inference
A charged straw is taken near the uncharged straw. Attraction Opposite charges attract, or an uncharged object attracts a charged one.
Two straws carrying similar charges are brought near each other. Repulsion Like charges repel each other.
A charged straw and the oppositely charged cloth used for rubbing are brought near each other. Attraction Opposite charges attract each other.

Experiment 2

1. Aim: To observe how objects can be charged by contact and induction and how they interact with other materials.

2. Requirements: plastic comb, paper pieces, uncharged comb, water tap (for a thin trickle of water), and balloon (optional).

Part 1: Charging by Contact

Procedure:

  1. Rub a plastic comb on a piece of paper to charge it.
  2. Touch this charged comb with an uncharged comb.
  3. Take the second comb close to the paper pieces and observe what happens.

Conclusion:

The second comb also gets charged through contact and attracts the paper pieces.

Part 2: Charging by Induction

Procedure:

  1. Rub a comb or balloon on your hair to charge it.
  2. Hold the charged comb near a thin stream of water from a tap.
  3. Observe how the water reacts.
  4. Move the comb away and observe if the water returns to normal.

Conclusion:

  • When the charged comb comes near, the water is attracted to it.
  • When the comb is removed, the water stops being attracted and usually flows again.
  • This happens because the opposite charges attract, and when the comb is removed, the water becomes neutral again.

This experiment shows that objects can be charged by contact or induction, and opposite charges attract each other.

Generation of electric charge

Experiment 3

1. Aim: To observe how objects interact through induction, attraction, and repulsion when charged and uncharged objects come close to each other.

2. Requirements: Negatively charged balloon, uncharged aluminum ball, tubelight and polythene bag (for another part of the experiment)

3. Procedure

Part Steps Observation Reason
Part 1: Balloon and Aluminum Ball Experiment Figure A: Bring the uncharged aluminium ball close to the negatively charged balloon. The aluminium ball is attracted to the balloon. Opposite charges are induced in the aluminium ball.
  Figure B: Allow the aluminum ball to touch the balloon. Both the balloon and the ball now carry the same charge. Charges transfer, making both objects similarly charged.
  Figure C: Move the aluminium ball away after it has touched the balloon. Both objects repel each other. Like charges repel each other.
Part 2: Tubelight Experiment Place a spent tube light in a dark room and rub it with a thin polythene bag. The tube light glows faintly. Rubbing produces a small electric discharge inside the tube light, causing it to emit light.

Effects of electric charge 

4. Conclusion

  • Attraction: When an uncharged object comes near a charged object, opposite charges are induced, and they attract.
  • Repulsion: When both objects gain the same charge, they repel each other.
  • Tubelight Glow: Rubbing generates an electric discharge, causing the spent tubelight to glow faintly. This shows how friction can produce small electric effects.
 
 
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