2. How is matter electrified? There are three methods:

Friction method

One of the simplest methods of electrifying matter is by friction. The process consists of rubbing two objects together, causing the transfer of electrons from one object to the other, even if the bodies were initially neutral .

Look at the following image. What do you think will happen if we rub the balloon with the jersey and then release it near by?

Simulation by PhET Interactive Simulations, University of Colorado Boulder, en https://phet.colorado.edu CC-BY-4.0

1. Initially, the jersey and the balloon are neutral bodies. They have the same number of positive and negative charges.

Simulations by PhET Interactive Simulations, University of Colorado Boulder, en https://phet.colorado.edu CC-BY-4.0

2. Rubbing the balloon with the sweater transfers electrons from the sweater to the balloon. The balloon becomes negatively charged and the sweater becomes positively charged. If we drop the balloon near the sweater, it is attracted to it.

Extension: Experiment

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In this simulator you can try to experiment as we have just seen, with the balloon, the jersey, a second balloon and the wall.

Simulation by PhET Interactive Simulations, University of Colorado Boulder, en https://phet.colorado.edu CC-BY-4.0

What sign is the charge that the balloons acquire when you rub them with the sweater ?

What happens when you bring the two balloons close to each other?

What is the difference between the force that appears between the balloons and the force that appears between a balloon and the jersey ? What do you think is the reason for this difference ?

Why do you think it is the balloon that is attracted to the sweater and not the sweater that is attracted to the balloon?

What happens if you bring a balloon close to a wall without actually touching it ?

Continue reading the topic and you will find the physical explanation for these observations.

Contact method

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Another common method to electrify a body is through direct contact with another charged body. When a charged object comes into contact with another body with no net charge, electrons can be transferred from one to the other. The second object acquires thus some of the charge of the first .

If a negatively charged object touches an uncharged object, electrons will move from the negative to the neutral one. The charges distribute between them, so both are charged with the same charge (negative charge). If a positive object comes into contact with a neutral object, electrons will move from the neutral to the positive one, attracted by it, so that the object that was initially neutral will also acquire a positive charge.

Look at this scene. What do you think will happen if John rubs his foot with the floor and then touches the metal door handle?

You can see the answer in this video:

Simulation by PhET Interactive Simulations , University of Colorado Boulder, at https://phet.colorado.edu CC-BY-4.0. Modified by Ana Dapena Mora CC-BY-SA

Induction method. Interactive video (4 min)

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Induction is a method used to charge a body electrically without the need for direct contact. In this process, a charged object is brought close to an uncharged object, which causes a redistribution of the electrical charges in the uncharged object. This results in a difference in electrical charge between different parts of the previously uncharged object, even though there is no transfer of electrons. This is what happens when the balloon in the first simulation approaches the wall.

A common example of contact electrification is the operation of an electroscope. An electroscope is a device used to detect charges. It consists of two movable plates suspended from a bar with a sphere at its top. All of this material is made of metal. Part of the bar and the plate are inside a glass bell jar.

In the next video we are going to use it to see how an object is charged by induction.

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Carga de un electroscopio por contacto e inducción

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Resultados

Conduction, induction and induction and grounding ina an electroscope. Interactive video created by Ana Dapena Mora based on the Brand Landale, LD Industries Physics 30. video. Youtube, CC-BY

Carga de un electroscopio por contacto e inducción

Video audio transcription

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In this file you have the written transcription of the audio of the video: "Charging an electroscope by contact and induction"

Video audio transcription: (New Window)

Comprenhension exercise. Choose the correct word

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Sometimes when we are in the supermarket and push a shopping cart, it gets charged by, space, Cloze (1): with the ground. Then, your brother touches the cart and exclaims, "Ouch!" He has received an unpleasant electrical shock by, space, Cloze (2): .

This can also happen when we touch a car that has been moving. We can get a shock by, space, Cloze (3): with the charge that the car has acquired through, space, Cloze (4): with the air.

When we rub a pen with our sweater, it gets charged by, space, Cloze (5): . If we then bring it close to small pieces of paper, without touching them, they get charged by, space, Cloze (6): , and will be attracted to the pen. You can try it!

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Sometimes when we are in the supermarket and push a shopping cart, it gets charged by friction with the ground. Then, your brother touches the cart and exclaims, "Ouch!" He has received an unpleasant electrical shock by contact.

This can also happen when we touch a car that has been moving. We can get a shock by contact with the charge that the car has acquired through friction with the air.

When we rub a pen with our sweater, it gets charged by friction . If we then bring it close to small pieces of paper, without touching them, they get charged by induction , and will be attracted to the pen. You can try it!

Reinforcement: Mulltiple choice

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Question

1. The method we would use to charge a body with another that has no charge would be:

Answers

Option 1

friction

Option 2

contact

Option 3

induction

Feedback

Correct Option

Incorrect. In the contact method, the charge is transferred from one charged object to another by touching it. The correct option is "friction".

Incorrect. In the induction method, it is necessary that one of the objects is charged to cause the movement of the charges in the second object. The correct option is "friction"

Solution

Correct Option (Feedback)
Wrong (Feedback)
Wrong (Feedback)

Question

2. The method that causes a redistribution of charges in another object without a transfer of electrons is:

Answers

Option 1

friction

Option 2

contact

Option 3

induction

Feedback

Incorrect. In the contact and friction methods, objects touch each other and the charge passes from one object to the other. The correct option is "induction" since the objects do not touch each other and the charge cannot pass from one to the other.

Correct Option

Solution

Wrong (Feedback)
Wrong (Feedback)
Correct Option (Feedback)

Question

3. When we dry our hair with a plush towel we notice that it makes the hair bristles. The hair has become electrified by:

Answers

Option 1

friction

Option 2

contact

Option 3

induction

Feedback

Correct Option

Incorrecto. La toalla y el pelo eran neutros, pero al frotarlos entre sí pasa carga de uno al otro. Se han cargado por frotamiento.

Incorrect. The towel and the hair were neutral, but when they were rubbed together, a charge was transferred from one to the other. They became charged by friction.

Solution

Correct Option (Feedback)
Wrong (Feedback)
Wrong (Feedback)

Question

4. When we get an electrical shock by touching another person, we have been electrified by:

Answers

Option 1

friction

Option 2

contact

Option 3

induction

Feedback

Incorrect. When two bodies simply touch each other, and one of them is charged, the charge transmission is by contact.

Correct Option

Incorrect. When two bodies simply touch each other, and one of them is charged, the charge transmission is by contact.

Solution

Wrong (Feedback)
Correct Option (Feedback)
Wrong (Feedback)

Question

5. If we bring a positively charged object close to an electroscope, it becomes charged:

Answers

Option 1

positively

Option 2

negatively

Option 3

it remains neutral.

Feedback

Correct Option

Incorrect. Electrons move from the electroscope to the positive body, attracted by it, and leave the electroscope with fewer negative charges than positive ones. It is left with an excess of positive charge.

Solution

Correct Option (Feedback)
Wrong (Feedback)
Wrong (Feedback)

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