Vật nhiễm điện là gì? Vật nhiễm điện bằng cách nào? Ví dụ?

What is an electrified object? How are objects electrified? Eg? Some multiple choice exercises on electrified objects? Instructions for solving Grade 7 Physics Exercises Lesson 17 – Electrification due to rubbing? Instructions for solving lesson 17 Physics 7 – Workbook?

The phenomenon of electrified objects is common in our daily lives. Therefore, there are lessons in this 7th grade Physics program in Vietnam. So what exactly is an electrified object? How are objects electrified? Proving examples? If you are also interested in this issue, then follow our article below.

1. What is an electrified object?

An electrically charged object is understood as an object capable of attracting or repelling other objects or releasing sparks to other objects. In essence, an object becomes electrically charged when it gains or loses electrons.

In fact, the phenomenon of electrified objects occurs very often in life, for example, on cold days, you often wear a hat to keep warm when going out, and when you remove the hat, you can easily see the damaged hair. suck on the inside of the cone. That’s because between the hair and the hat are electrified. Or in hot weather, when you use a comb to brush your hair, you will find that your hair is attracted by the comb and pulled straight out….

According to current research, there are three ways to make objects electrified: electrified by rubbing, electrified by contact and electrified by response.

2. How do objects become electrified? Eg?

As discussed above, an object can become electrified by rubbing, contact, or response. Specifically, their contents are as follows:

2.1. Electrification by rubbing:

When two electrically neutral objects rub together an atom of an object loses some electrons and becomes positively charged. The other object will receive the other object’s electrons and will be negatively charged. According to the law of conservation of charge, the total charge of two objects after contact is zero.

In a word, electrified objects due to rubbing are objects that, after being rubbed, will have the ability to attract other objects. To check if objects are electrified after being rubbed, we can use an electric tester to see if the lights are on or see if they attract other light objects.

Eg: Use a plastic ruler, scraps of paper, plastic crumbs, or a small sphere made of foam. When one end of a plastic ruler is brought close to paper or plastic scraps or foam balls, nothing can be observed. When using a dry cloth, rub one end of the plastic ruler, and then bring the end close to a piece of paper, plastic, or a styrofoam ball. Observation will see the phenomenon of these paper and plastic debris clinging to the plastic ruler that has been rubbed with cloth. In other words, the tip of the plastic ruler attracts these small particles.

=> A plastic ruler is an electrically charged object due to rubbing with a piece of cloth.

2.2. Electromagnetic contact:

Contact electrification is when an electrically charged object and an uncharged object are brought into contact (without friction or friction) but simply placed very close to each other or placed on top of each other. the rest will be electrified with the same sign as the electrified object. Because the two objects are charged with the same sign, there will be a phenomenon of repelling each other (with opposite signs attract, with the same sign repel).

see more: What is the rated current? Symbols, formulas and calculations?

Simply put, contact electrification is when free charges (specifically electrons) inside a charged object move to an uncharged object, causing both to become electrified.

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Accordingly:

There are two types of positive and negative charges

An object becomes negatively charged when the number of electrons is greater than the number of protons.

An object becomes positively charged when the electrons are smaller than the number of protons.

– If the number of electrons and protons in an object are equal, the object is neutral.

Eg: An electrically neutral iron rod placed near a negatively charged aluminum ball will be pushed away.

2.3. Electrification due to response:

Reciprocal electrification is what occurs when a neutral object is placed near a charged object. If the object is negatively charged, it will push the electrons of the neutral object away from it, causing the neutral object to split into two different charge regions, the area near the charged object will be positively charged and the far part of the charged object will be negatively charged. .

see more: What is electromagnetic wave? What are the characteristics and applications of electromagnetic waves?

And vice versa, if the object is positively charged, it will attract the electrons of the neutral object closer to it, causing the region of the neutral object close to the charged object to become negatively charged and the part far away from the charged object will become positively charged. .

In general, an electrically neutral object when in close contact with an electrically charged object, the two ends of the neutrally charged object will be charged with opposite charges, the end that is near the charged object will be charged. opposite sign to the charged object. This phenomenon is called reactive electrification or electrostatic induction.

Eg: When a charged metal ball is brought close to a conductor, the far end of the sphere is charged with the same sign as the sphere, and the end near the sphere is charged with the opposite sign.

3. Some multiple-choice exercises on electrified objects:

Question 1. Choose the correct answer. Using a dry cloth to rub, which of the following objects can be charged:

A. Iron rod

B. Steel bar

C. Plastic rod

D. Wooden stick

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Answer C.

Verse 2. Fill the right words in the blank. Many objects, after rubbing, have the ability to……………electric tester pen bulb

A. Break

B. Brighten

C. Turn off

D. All A, B, C are wrong

Answer B.

Verse 3. Choose the correct answer. One of the causes of electrified thunderstorm clouds is:

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A. Strong rubbing between water droplets in the rising air stream

B. Strong rubbing between air currents

C. Wind makes clouds electrify

D. All three sentences above are wrong

Answer A.

Verse 4. Choose the correct answer. When you bring a plastic ruler close to a hair

A. The ruler sucks the hair

B. The ruler pushes the hair

see more: What is refraction of light? Law of refraction of light?

C. The ruler, after rubbing it with a dry cloth, will absorb the hair

D. The ruler, after rubbing against the dry cloth, will push the hair away

Answer C.

+ Before the plastic ruler was rubbed, it did not react with the hair

+ After the plastic ruler is rubbed with a dry cloth, it becomes an electrified object and can attract hair

Question 5.Choose the correct answer. The glass rod, after being rubbed with a piece of silk, is capable of:

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A. Can suck up the dry cloth

B. Can suck up a piece of plastic

see more: When is an object negatively charged? When is an object positively charged?

C. Can suck up a piece of wool

D. Can suck the plastic ruler

Answer B.

The glass rod, after being rubbed with silk, is capable of absorbing small dry objects such as scraps of paper, scraps of wool, small hairs or pieces of dry cloth.

A – wrong because I don’t know if it’s a dry cloth or a piece of dry cloth

D – wrong because the glass rod after being electrified by rubbing does not attract the plastic ruler

Verse 6. Choose the correct answer. Using a dry cloth to rub, which of the following objects can be charged:

A. Iron rod

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B. Steel bar

C. Plastic rod

D. Wooden stick

Answer C.

Plastic pipes can become electrified by rubbing it with a dry cloth.

Verse 7. Fill the right words in the blank. Many objects, after rubbing, have the ability to……………electric tester pen bulb

A. Break

B. Brighten

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C. Turn off

D. All A, B, C are wrong

Answer B.

4. Instructions for solving Grade 7 Physics Exercises Lesson 17 – Electromagnetism due to rubbing:

Lesson C1 page 49 physics textbook 7 lesson 17:

Content: Explain why on dry days, especially dry days, when we comb our hair with a plastic comb, many hairs are pulled straight out by the plastic comb?

Solution: Because when combing hair on dry days, the comb causes the hair and the comb to be rubbed, creating an electric charge. From there, the hair and comb are attracted to each other.

Lesson C2 page 49 physics textbook 7 lesson 17:

Content: When blowing on the tabletop, the dust flies away. Why does the electric propeller blow strong wind, after a while there is a lot of dust clinging to the propeller, especially at the edge of the blade cutting into the air?

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Solution: When the fan is operating, the propeller rotates creating friction with the air. Since then, the fan blades are charged and attract dust particles around them, so when used for a long time, the fan gets quite dusty. Especially the edges of the fan are exposed to the most air, so they are also dusted the most.

Fan is a common phenomenon for charged rubbing.

Lesson C3 page 49 physics textbook 7 lesson 17:

Content: On dry weather days, when cleaning mirrors, window glass or TV screens with a dry cotton cloth, we still see dust clinging to them. Explain why?

Solution: Because when using a dry cotton towel in contact with objects, it will create an electric charge. And make the cloth dust on the towel be attracted to those items. So if you want them to be cleaner, it’s best to use damp newspaper so that they don’t get charged.

5. Instructions for solving lesson 17 Physics 7 – Workbook:

After the knowledge and examples as well as support to answer questions above, you should be able to understand some of the lesson. And to improve your thinking ability, the article will guide you to solve the exercises physics 7 lessons 17 in the workbook.

Lesson 1: Have the following items: a wooden pencil, a plastic ballpoint pen, a paper cutter blade, a metal spoon, a plastic comb, and a piece of paper. Scrub these objects with a dry cloth one at a time, and then bring them one by one near the scraps of paper. Words indicate which objects are electrified and which are not.

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Answer: Electrically charged objects include plastic ballpoint pen cases, plastic combs. Non-electrified objects include: wooden pencils, paper scissors, pieces of paper, metal spoons.

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Exercise 2: Using a dry cloth to rub, which of the following objects can be charged?

Answer: D. Because when using a dry cloth to rub it, it can cause the plastic pipe to carry an electrical charge, causing an electric charge.

Exercise 3: Do an experiment as shown in Figure 17.1, in which using a sewing needle (or awl) to punch a small hole near the edge of a plastic bottle (eg mineral water bottle) to create a small jet of water. Bring a flat plastic ruler close to the water jet (the water jet is almost full of the bottle) in two cases: when not rubbing and rubbing the plastic ruler.

Answer: When the ruler has not been rubbed, the water still flows straight down when the ruler is brought closer. However, after the ruler is rubbed, an electric charge occurs, so when the ruler is brought close, the water is attracted to the ruler.

Lesson 4: Explain the phenomenon mentioned at the beginning of lesson 17 in the textbook: “On dry days, especially on dry days, when taking off wool, felt or synthetic outerwear , we often hear a small crackle. If we were in a dark room then, we could still see tiny flashes of light.”

Answer: Because when we move, we also cause the clothes to rub against each other, causing electricity. Sparks should appear and the air expands, causing small crackling sounds and tiny flashes of light.

Exercise 5: Which of the following statements is true?

Answer: C. Since magnets are magnetic, they are not electrically charged, and the ground has gravity, so it attracts everything to the ground.

see more: What is thermal energy? Formula for heat capacity? Its application?

Lesson 6: How can I make an electrified plastic ruler?

Answer: D. Rubbing with a dry cloth is the best way to electrify the ruler.

Lesson 7: Using a piece of wool repeatedly rubbing a piece of plastic film, this piece of plastic film can absorb the paper scraps? Why?

Answer: B. Because they are electrified by rubbing, they attract paper scraps.

Lesson 8: A piece of unelectrified glass is hung on a shelf by a flexible wire as shown in Figure 17.2. Rub one end of the plastic ruler and then bring the tip of the ruler closer to one of the above-mentioned glass rods. Ask what happened and why?

Answer: Because the ruler is electrified when rubbed, the glass rod is attracted to the ruler.

Lesson 9: In textile factories, there are often parts that brush the fibers of the fabric. Under normal conditions, these fibers are easily tangled and tangled. Explain why? What measures can be used to overcome this adverse phenomenon?

Answer: Because when brushing occurs, an electrical charge occurs, causing the fibers to be attracted to each other. To solve the above problem, the combing part needs to use insulating material.

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