On a rainy day, when two oppositely charged clouds come close to each other, the potential difference between them can reach millions of volts. There is a spark between the two clouds and we see a flash of lightning. A few seconds later we hear an explosion, which is thunder (because the speed of light is faster than the speed of sound, we see lightning first). When a charged thunderstorm cloud passes near the ground to open areas, encounters a high-altitude object such as a tree, a person holding a shovel, etc., there will be an electric spark between the cloud and the ground.
Download the VietJack app. See answers faster!
1. To identify an electrified object:
Based on the characteristics of the electrified object, it is capable of attracting other objects or releasing sparks to other objects. So if we want to know if an object is electrified or not, we bring the object to be recognized close:
– Light objects, if:
If it attracts light objects, the object becomes charged.
If it can’t attract light objects, it’s not electrified.
– Other electrified objects, if possible:
If there is an electrical discharge, the object is already electrified.
+ If there is no discharge, the object is not charged.
2. Ways to make an object electrified:
– Rubbing the object against another object such as wool, plastic, hair, ebonite, etc. (Electricity due to rubbing).
– Bring the object close to the electrified object, the object will become electrified. Electrically charged as an object is called response electrification.
– If the object comes into contact with an electrified object, the object will become electrified. Such electrification is called contact electrification.
Example 1: The car runs for a long time, after getting off the car, touching the side of the car sometimes feels like an electric shock. Reason:
A. The vehicle’s electrical components are damaged.
B. The car’s wall is rubbing against the air, so the car is electrified.
C. Due to some electrical appliances nearby working.
D. Because there is a thunderstorm outside.
Because the car’s wall rubs against the air while driving, it becomes electrified, so it’s like being electrocuted to the touch.
Example 2: At what temperature can electrification by rubbing occur?
A. High temperature
B. Low temperature
C. Human body temperature
D. Any temperature
Electromagnetism can occur at any temperature
Example 3: Please explain why in winter, when we take off our sweater or our stomach, we often hear a crackling sound, in the dark we can still see tiny light spots, the shirt often sticks to the body when pulled up?
Because when we wear a sweater, our body rubs against the shirt, so both the body and the shirt are electrified. When we take off the shirt, the parts of the shirt will discharge due to close contact, making us see tiny light spots, accompanied by the discharge is the heating of the small part of the air there, causing the air to expand rapidly. cause a crackling sound. Because the shirt and body are electrified, it is attracted to the body.
Question 1: Which of the following objects exerts a force of attraction on an electrically charged plastic comb?
A. Paper scraps
B. Metal ball
C. Small stream of water flowing from the faucet
D. All three objects above
An electrically charged object can attract small, thin, light objects, or discharge electricity into other objects.
An electrically charged plastic comb can exert suction on even a piece of paper, a metal ball, or a small stream of water flowing from a faucet.
Verse 2: In winter, when combing hair with a plastic comb, which of the following phenomena usually occurs:
A. The plastic comb is electrically charged.
B. The hair is electrified
C. Both hair and comb are electrified.
D. Neither the hair nor the comb are electrified.
Both the hair and the plastic comb are rubbed so they both become electrified.
Question 3: In what state can substances become electrified?
A. Solid State
B. Liquid state
C. Gas state
D. All three states above
Substances in the solid, liquid, and gaseous states can be electrified.
Question 4: Dust clings to electric fan blades because:
A. When the fan runs fast, the dust gets caught up, so the dust collects.
B. The impeller rubs against the electrified air and picks up dust.
C. Rotating impeller creates swirls of dust.
D. When the fan turns, the front air blows the dust into the blades.
When the propeller rotates, it rubs against the air, so it becomes electrically charged and attracts small dust particles.
Question 5: Which of the following figures shows that the spheres have become electrified?
A. 1 and 2
B. 2 and 3
C. 3 and 1
D. 1, 2 and 3.
When the spheres are electrified it can either attract or repel the other. So the spheres in Figures 2 and 3 are already electrified.
Question 6: Please explain the phenomena in the figures below:
a) The rubber ball, after being rubbed, becomes electrified, so it is able to attract light metal cans.
b) The plastic ruler was rubbed so that it was able to absorb a small stream of running water.
c) The plastic ruler, after being rubbed, becomes electrified, so it can absorb small and light objects such as paper chips and foam chips.
d) The TV screen when wiping has rubbed with the cloth, so it becomes electrified, dust particles or fibers can be sucked in by it.
Verse 7: Please explain why petrol and oil tankers often have a chain that drops to the road surface?
Vehicles carrying gasoline and oil when moving on the road will be electrified due to the car’s trunk rubbing with the air, the wheels rubbing against the road surface. If the amount of charge is large enough, it will cause a discharge. The iron chain connecting the truck’s trunk to the ground helps the electric charges to follow the chain to the ground, avoiding the risk of fire and explosion.
Verse 8: Why is it that in the textile factories, garment factories, cement factories, people often put in the chimneys large metal plates that have been electrified? (as picture)
In the air of textile, garment or cement factories, there is a lot of dust, these dust particles are very small in size, when inhaled, they will greatly affect the health of workers in the factory. Therefore, to clean the air, people often place large electrified metal meshes in the chimney, because the electrified object has the ability to attract other objects, especially small and light objects such as dust particles. , cotton, fabrics…
Verse 9: Why should we not stand under tall old trees when we go outdoors if we encounter a thunderstorm?
During thunderstorms, lightning strikes often occur, causing death danger. This lightning phenomenon occurs because the clouds move quickly and rub against each other, rubbing against the air for a long time, so the clouds are strongly charged. When the clouds come close to each other or near the tops of mountains and tall trees, electric discharge occurs to form lightning and lightning. There the temperature is very high, the layer of air there is hot and expands rapidly to form an explosion called thunder. Lightning often strikes sharp objects, protruding above the ground such as tall trees, high mounds, etc. Therefore, we should not stay under old trees, tall trees to avoid being struck by lightning, causing death danger.
Question 10: Without using everything else, how can we tell if a wick ball hanging from a thin thread is electrified or not?
A simple way to check without using other objects to see if a wick ball hanging from a thin thread is electrified is to bring your finger close to the wick. If:
– If the ball is deflected towards the finger, the ball becomes electrified.
– The ball is not deflected towards the finger, still standing upright, the ball is not electrified.
Question 11: Explain why when refueling an aircraft that has just landed at an airport, one must connect the fuselage to the ground?
Airplanes have just completed a long flight, the fuselage rubs against the air, so there will be a lot of charge. Connecting the fuselage to the ground will help transfer this charge to the ground, thereby avoiding the risk of fire and explosion when refueling.
See more selected types of Grade 7 Physics exercises, with other good answers:
See more series To study Physics 7 well or other series:
Introducing VietJack Youtube channel
Ask for exercises on the app, VietJack teachers answer for free!
- More than 20,000 multiple choice Math, Literature and English questions for grade 7 with answers
There is VietJack app on the phone, solve textbook exercises, SBT Compose, Sample Literature, Online Exam, Lecture….for free. Download the app now on Android and iOS.
Free facebook learning group for teen 2k9: fb.com/groups/hoctap2k9/
Follow us for free on social networks facebook and youtube:
Series Theory – Physics 7 exercises with answers Our curriculum is compiled to follow the content of the Grade 7 Physics program.
If you find it interesting, please encourage and share it! Comments that do not match website comment rules You will be permanently banned from commenting.