][ أطلب أي بحث أو تقرير هنااااا فقط ][-3

[غزلان البراري]

ابي حق انج 105

فقرات ( مقدمة / عرض / خاتمة )

السلبيات والاجابيات

ضرووووووووووووووووري

لو سمحتوووووووو

ملاحضة: غير الي في الموضوع المثبت

 

A. Keeping animals in zoos

 

Keeping animals in zoos has many advantages and disadvantages.

 

One of the most obvious advantages of keeping animals in zoos is that animals are looked after when they are sick. This can give them the best of care and also protect them from diseases. In addition to that, it’s a place where people can see and learn about animals. Finally, it can be a good place for scientists to study animals and their needs, so that they can protect them becoming extinct.

 

On the other hand, keeping animals in zoos has a lot of disadvantages. First of all, they are prevented from their freedom, which can cause them to be unhappy and uncomfortable. Furthermore, animals are usually forced to do silly tricks to entertain visitors of the zoo, and that might cause them discomfort. Last but not least, keeping animals in zoos can disturb the natural balance of wildlife.

 

In conclusion, keeping animals in zoos can be the best way to study them and save them from becoming extinct by breeding programs. However, it would be better to keep them in wild protected areas, and study them there.

 

B. Owning a television

Many people like watching television and spend hours sitting watching that small screen. However this has both advantages and disadvantages.

 

One of the obvious advantages of having a television is that it offers cheap and convenient entertainment which nearly everyone can afford. This is especially important for people who are alone all day or for large families who can’t afford to go out to cinemas. What is more, television can have a serious educational side and there are plenty of good current affairs programmes which are very informative.

 

On the other hand, having a television can have certain disadvantages. While it is good to have such cheap and convenient entertainment in your own living room, it may also mean the end of reading and conversation for large parts of the evening. Furthermore, although there are many good programmes on television, there is often too much blood and violence on screen. This can be especially harmful for children.

 

All in all, I think that having a television is important and watching it is useful if one knows how, when and what to watch.

 

C. Studying abroad

When you want to be different in your family you should do something different also. So when you also want to be the best one of them you should look after your study.

 

One of the most important things that you must take care of is your future. So you should try to build a good one by studying in good places. I hope that my brothers and I study in the best places. People always think that studying abroad is a good way to start our lives. However, it has some advantages and disadvantages.

 

Let’s look at the dark side first. When you are in a different country you might be affected by the culture there. Also, you will find yourself in a place that you can’t get along with at first. This means that you will have to hold a lot of responsibilities. Furthermore, you will be far away from your family and you will feel lonely.

However, studying abroad has a lot of advantages. In the first place, schools in other countries teach students in a better way than ours’ do. In addition to that, they give students a higher certificate. Last but not least, studying abroad gives the student time to learn different things like housekeeping for example.

 

Finally, we can say that studying abroad is a good way to improve our language and education. But in the same time it can affect our tradition and culture.

 

D. Traveling abroad

Many people travel abroad for several reasons. Some prefer not to do so. Personally, I believe traveling abroad has both advantages and disadvantages.

 

One of the most obvious advantages of traveling abroad is that it introduces new cultures and gets you to know the customs and traditions of other nations. Furthermore, traveling abroad is a great mean of leisure and entertainment. Finally, by traveling abroad you can receive education by entering courses in high reputable universities and institutes.

 

On the other hand, traveling abroad can have many disadvantages. First of all, it can cause you to get affected by other cultures and forget your own. What is more, you can face very risky situations while being abroad. Being foreign to the country, you might find it difficult to escape these situations. Last but not least, many people have a tendency to spend too much money when being abroad. When they return home, they might face financial problems because of this behaviour.

 

In conclusion, traveling abroad might be of benefit to the traveler, but it also might cause him misery. I think the kind of person the traveler is determines whether traveling abroad is good or bad for him.

 

E. Owning a mobile phone

One of the most important developments in the field of telecommunication is the mobile phone. I believe the mobile phone has both advantages and disadvantages.

 

We are now in the 21st century, and it is necessary to contact with other sides of the world. The mobile phone makes this easy. All my family and I have got a mobile phone. Furthermore, the mobile phone can help one get out of risky situations. Finally, the mobile is small and easy to carry.

On the other hand, owning a mobile phone can cost a lot of money. In addition to that, it can also cause one’s body harm if he uses it too much. Last but not least, mobiles can be annoying if the network isn’t very strong.

 

Owning a mobile phone in this age has become very essential. However one should control himself and only use it for important calls.

 

F. Owning a car

Every family has one or two cars or two nowadays. But, owning a car has both advantages and disadvantages.

 

One of the most obvious advantages of owning a car is that a car allows people to move around freely. Furthermore, there is no need to wait for a bus or a taxi, so it saves time. Moreover, owning a car is a comfortable way to travel. Especially in the winter. It can protect you from standing under the rain or in the cold. Last but not least, a car makes your life safer. You will not need to walk down a dark street to wait for a bus or take a taxi.

 

On the other hand, owning a car has a lot of disadvantages. First of all, owning a car can be very expensive. As well, the fuel costs a lot and a car is expensive to maintain. Although it allows people to more around freely, it is very exhausting to drive in rush hour traffics. Moreover, it causes death to many people every day. Finally, if you leave your car in the street it might get stolen.

 

Although owning a car has some disadvantages, it has more important advantages. Therefore, I think it is very important nowadays to own a car.

 

G. Living in a big family

It is known that people in the past used to have big families. They took it as an advantage. However, nowadays, people think it has some disadvantages.

 

One of the most obvious advantages of having a big family is that you can never be alone (isolated) or feel bored. Therefore, you will always fell safe and secure. Furthermore, brothers and sisters can help each other in education. They can exchange some of their experiences. Moreover, they support each other when they face a problem. What’s more, if the children grew up and worked, they may help their parents financially. More than that, children can wear each other’s clothes or play with each other’s toys.

 

 

On the other hand, having a big family has its disadvantages. In the first place, it may be difficult for the parents to control them and provide them with sufficient food, clothing and education expenses. Moreover, they won’t be able to go out a lot, because it will cost too much. For instance, if you decided to go to the cinema, it will cost at least BD 2 for each one. Added to that, having a big family means a lot of fighting. Everyone wants to watch a different program and eat a different meal …etc. That means their needs will increase.

 

Finally, is having a big family good or bad? In my case, living in a normal family is the perfect thing for me.

 

H. Living in a city or in a country?

A lot of people want to live in a city, so some of them moved from the country to the city looking for better chances. But still there are some people who prefer to live in a country. So is it better to live in a city or in a country?

First, let’s talk about living in a city. It’s preferred as a place to live in because it shows you a variety of people, races and cultures. Also, it’s more exiting with its movies, theatres and restaurants. Then, there are lots of interesting shops, which make your shopping great and comfortable. Finally, the most important advantage is that it gives you more job opportunities.

On the other hand, some people don’t prefer to live in the city because it has a lot of drawbacks. One of them is the traffic jams and parking problems. Also, the polluted air, which affects our health. In addition, living there is so expensive. Furthermore, the shops are always crowded, so that makes us worried. The most important thing is that living there can be more dangerous because there are so many crimes.

Now, we’ll take about living in a country. Life in the country is very peaceful and quite. The people are so friendly and kind. Then, there is the fresh air, which comforts us. You live there with out pollution, noise, stress or crimes.

From anther way, living in the country can has its disadvantages. One of them is that you’ll be isolated from the outer world and away from modern life. Then there are less jobs, schools and hospitals, because off all these, we see that the education and health levels are so low.

In my point of view, I think I prefer living in the city to be close to the modern technology, and visiting the country is just for talking rest and change.

 

[ZoZo 88]

مشكورة أختي ع المساعدة وماقصرتي

[alimar]

لو سمحتوا بغيت تقرير قصد 312

 

في احد المواضيع التالية:

 

التنمية الاقتصادية

التخطيط الاقتصادي

التجارة الدولية

المالية والاقتصاد الدولي

مؤسسة نقد البحرين

منظمة التجارة العالمية

[نواف502الدوسري]

ابي بحث ضروري اذا ماعليج امر

ويكون فيه

مقدمه

وعرض وخاتمه

[ali_koo]

السلام عليكم

 

عندي طلب بسيط واتمنى انكم تسوونه لي

 

ابي بحث عن الــ OP314 office practice

 

عن الـ Finding Work

 

اتمنى انكم تييبونه لي قبل تاريخ 1/4/2006

 

تحياتي

اخوكم علي كوو

[قلوب الحزن]

لو سمحتي بغيت عن تقرير عن فلم انجليزي مال ثالث اعدادي

 

تكون الصفحات وايد بس ما تكثر عن 10 صفحات

 

 

[جرح انسانه]

ابي بحث ضروري اذا ماعليج امر

ويكون فيه

مقدمه

وعرض وخاتمه

تقرير وشوو ؟؟؟؟

 

 

 

لو سمحتي بغيت عن تقرير عن فلم انجليزي مال ثالث اعدادي

 

تكون الصفحات وايد بس ما تكثر عن 10 صفحات

تفضلي هاي عن فلم

 

The story begins fifty years before the present day, with a description of how the Riddle family was mysteriously killed at supper, and their groundsman, Frank Bryce, was suspected of the crime, then declared innocent. Frank Bryce, now an elderly man, wakes in the night to see a light in the window of the abandoned Riddle House. He investigates and overhears Voldemort and Wormtail plotting to kill a boy named Harry Potter. Voldemort takes note of him and kills him on the spot. Harry Potter wakes up in the night with a throbbing pain in the scar Voldemort gave him. He worries that Voldemort is nearby, and he writes to Sirius Black, his godfather, mentioning the pain in his scar.

 

The next morning Harry's Uncle Vernon receives a letter from the Weasleys asking Harry to join them at the Quidditch World Cup, and Vernon grudgingly agrees to let Harry go. The following day, the Weasleys arrive in the Dursleys' boarded-up fireplace to pick up Harry. The Weasley twins "accidentally" leave a trick toffee on the ground, which Dudley eats, causing his tongue to engorge itself. The Dursleys panic and throw things at Mr. Weasley as the Weasley boys and Harry exit through the fireplace. Harry arrives at The Burrow, the Weasley household, and there he meets for the two eldest Weasley brothers, Bill and Charlie, and there, Mrs. Weasley berates the twins for making Weasleys' Wizard Wheezes and giving them to Dudley.

Early the next morning, the Weasleys, Harry and Hermione head off to the Quidditch World Cup. They travel by Portkey, a process that involves using a piece of trash as a touchstone for warping across space. They use the same Portkey as Cedric Diggory, another Hogwarts student, and his dad. Together they are carried to the World Cup campground. Upon arrival, the Weasleys, Harry and Hermione head off to pitch their tent. Soon, Ludo Bagman arrives, jubilant at the festivities, and makes a wager with the twins on the outcome of the Cup. Soon afterward, Mr. Crouch arrives, throwing Percy into a great reverent fuss. Before they leave, they allude to a mysterious event that will happen at Hogarts. Harry, Ron, and Hermione buy souvenirs and troop to the Top Box, where they meet Winky, a house-elf who is saving a seat for her master. The game begins, after a show from the respective mascots. In the end, Ireland wins, but Viktor Krum, the Bulgarian Seeker, catches the Snitch.

The night after the game, a crowd of Death Eaters, followers of Voldemort who escaped punishment, torture four Muggles by levitating them in the air. Harry, Hermione and Ron escape by fleeing into the woods, where Harry discovers that his wand is missing. Moments later someone fires the Dark Mark (the sign of Voldemort) using his or her wand. Winky the house-elf is found holding a wand at the scene of the crime. Mayhem ensues at the Ministry of Magic through the week.

Ron receives horrible second-hand robes from his mother and is upset. Amos Diggory brings news that a man named Mad-Eye Moody attacked an intruder at his house. Mr. Weasley runs to the Ministry to sort everything out. The Weasleys, Harry, and Hermione take taxis to the train station and board the train to Hogwarts. Upon arriving, after the Sorting ceremony and in the middle of dinner in the Hogwarts Great Hall, Dumbledore announces that the Triwizard Tournament between schools will take place this year at Hogwarts, and also that Mad-Eye Moody will be the new teacher of defense against the dark arts.

Mad-Eye Moody is a competent teacher. He turns Malfoy into a ferret for trying to attack Harry while Harry's back is turned. In class, Moody teaches Gryffindor the three unforgivable curses, Imperius, Cruciatus, and Avada Kedavra (the curse that killed Harry's parents). Meanwhile, Hermione founds a society that advocates freeing house-elves, who are slaves. She asks Harry and Ron to wear badges. As Defense Against the Dark Arts progresses, Harry learns to successfully ward off the Imperius Curse.

 

In late October, the delegates from Beauxbatons and Durmstrang arrive, and Ron is thrilled to see that Viktor Krum, a famous Quidditch player, has come with Durmstrang. On halloween night, the Goblet of Fire spits out the names of the champions who will compete in the Triwizard Tournament; along with Cedric Diggory, Fleur Delacour, and Viktor Krum, Harry Potter is selected. Mass chaos ensues, since Harry is too young. But because the Goblet's decision is final, it is generally decided that Harry is obligated to compete. Gryffindor House is triumphant, but Ron is sullen and envious, and he doesn't speak to Harry for quite some time. School resumes, and Harry is frustrated that few people believe he didn't place his own name in the Goblet of Fire. The first task approaches, and Harry is fretful; during the weighing of the wands, a reporter named Rita Skeeter accosts Harry and interviews him for what she says is a story about the tournament, but instead publishes a sappy, exaggerated article about Harry's tragic past.

A few nights before the task, Hagrid invites Harry for a late night walk, which ultimately turns into a glimpse of the first task: dragons. Harry hurries home, and in the Gryffindor common room fireplace, Sirius's head appears, warning Harry that Karkaroff, the head of Durmstrang, was a Death Eater and possibly still is dangerous, and that Moody was the Ministry's best dark wizard catcher ever, and is probably at Hogwarts for a reason. The next day, Harry warns Cedric about the first task; Moody overhears, commends Harry's decency, and hints that Harry should use his broomstick to get past the dragon. Harry and Hermione spend hours practicing summoning charms, and the day of the first task, Harry summons his broomstick and flies past the dragon, capturing the golden egg and receiving high marks. Everyone in Gryffindor is ecstatic, and Ron and Harry are reunited.

Soon afterward, Hermione drags Harry and Ron down to the kitchens, where they encounter Dobby, who is thrilled at his freedom, and Winky, Mr. Crouch's ex- house-elf, who is miserable at hers. In class, Professor McGonagall announces that the Yule Ball is approaching and that the champions must find partners; this is an unexpected and difficult task. Harry gathers his courage to ask Cho, but finds out that she is already going with Cedric. Hermione has a date, but won't say who it is; and she is annoyed when Ron asks her as his last-resort date. Finally, Harry and Ron procure the pretty but annoying Patil twins as their partners for the Yule Ball. On Christmas, the night of the ball, Ron wears his awful dress robes and spends the entire night staring at Hermione, who is there as Viktor Krum's date. Harry spends the whole night feeling miserable about Cho and Cedric, and so Harry and Ron leave the ball for a stroll, during which they overhear Hagrid telling Madame Maxime, the giant head of Beauxbatons, that he is half-giant. After the ball that night, Cedric hints for Harry to take a bath with the golden egg, but Harry is wary of this advice. Harry returns to Gryffindor tower to find that Hermione and Ron are having a huge fight about why she went to the ball with Krum instead of with him.

The next day, Hagrid is not teaching class. Rita Skeeter has written an article saying that his ancestors, who are giants, give him a violent and dangerous nature. He is embarrassed and refuses to emerge from his cabin. During a trip to Hogsmeade, Ludo Bagman offers to help Harry with the tournament and mentions that Mr. Crouch has stopped coming to work. Hermione insults Rita for writing such horrible articles. Harry, Ron, and Hermione return to Hogwarts, visit Hagrid, and persuade him to return. Hagrid is grateful for their loyalty, and he begs Harry to win the tournament. That night Harry takes the egg into the bathtub. It sings that he will have an hour to reclaim something valuable that has been taken into the lake. On his way back to his dorm from the bathroom, Harry, wearing his Invisibility cloak, checks his Marauder's Map and spies Mr. Crouch in Snape's office. In his surprise, he drops the golden egg, which makes a loud screeching noise. Filch and Snape appear instantly. Moody also appears, shoos away the other men and returns Harry's egg to him. Moody asks to borrow the Marauder's Map, which shows every part of Hogwarts grounds and castle, and where every person is within it.

The night before the second task, Harry still has not figured out how to breathe under water. He falls asleep in the library and is awakened in the morning by Dobby, who gives him a ball of gillyweed and sends him off to the lake, where the task is starting. The gillyweed gives Harry gills, so he swims easily through the lake, finding Hermione, Ron, Cho, and Fleur's sister asleep and tied together in a merpeople village. Harry waits to make sure all of the champions rescue their hostages before returning to the surface. Fleur never comes, so he returns with her sister and with Ron, coming up last, but gaining high marks for his moral fiber in his completion of the task.

Soon afterwards, Rita Skeeter publishes an article claiming that Hermione toys with the hearts of both Harry and Krum. The three friends read the article in potions class. After class, Harry overhears Karkaroff confiding fearfully in Snape that something on his arm has returned. The following day, Harry, Ron, and Hermione meet Sirius Black, disguised as a large black dog named Padfoot, in Hogsmeade. He informs them that Mr. Crouch's son was convicted as a Death Eater, and he finds it peculiar that Mr. Crouch has not been coming to work, as well as that he never showed up to take the seat saved by Winky, his house-elf, at the World Cup. Back at Hogwarts, Harry, Ron, and Hermione visit the kitchens to give a gift of socks to Dobby, who is delighted. Winky is still sad and currently drunk, and she mentions between hiccups that she is guarding a great secret for her ex-master. Around this time, Hermione begins getting hate mail for supposedly breaking Harry Potter's heart.

The four champions are taken to see the grounds for the maze, their third task, and on the way back, Krum pulls Harry into the forest to ask if he is at all romantically interested inHermione. When Harry answers no, a disheveled Mr. Crouch appears from the forest, speaking to trees and madly demanding to see Dumbledore. Harry runs to get Dumbldore while Krum waits with Mr. Crouch; when Harry returns, Mr. Crouch has stunned Krum and disappeared, much to everyone's puzzlement. Sirius sends Harry a letter warning him to be careful and to practice hexes for the third task; Harry tries to follow both instructions. In Divination class, Harry falls asleep and dreams about Voldemort, and he wakes up screaming and clutching his scar. Harry leaves class and goes to tell Dumbledore what happened. As he waits for Dumbledore to return to his office, he peers into a Pensieve and enters Dumbledore's memories of various Death Eater trials, including that of Ludo Bagman, Karkaroff, and Mr. Crouch's son. Dumbledore returns, pulls Harry from the memory-world, listens to his story, and says that he suspects that Voldemort is growing stronger.

The morning of the third task, Rita Skeeter prints an article about how Harry fainted in class and is possibly disturbed. The evening of the task, the four champions enter the maze, and Harry finds his path relatively manageable. Soon both Fleur and Krum are out of the running, and Harry and Cedric, the only remaining contestants, arrive at the trophy at the same time, and they both agree to touch it together. The trophy turns out to be a portkey, and it takes both boys to a far away graveyard, where a man in a hood instantly kills Cedric and ties up Harry. The man, Wormtail, drops the bundle he is carrying (Voldemort's current form) into a cauldron, as well as ashes from Voldemort's father, blood from Harry's arm, and Wormtail's own right hand. Voldemort resumes his body and rises from the cauldron. Voldemort presses a tattoo of the Dark Mark on Wormtail's arm, and suddenly Death Eaters begin appearing in a circle around them. Voldemort explains to Harry and his Death Eaters his fall from and rise back to power, and then he challenges Harry to a duel. Harry prepares for death, but he manages to use the disarming spell on Voldemort just as Voldemort cries "Avada Kedavra!" the killing curse, at Harry. The light from the two wands meets in midair and remains connected. Voldemort's past victims emerge from his wand and protect Harry once the wand connection is broken, giving him time to grab Cedric's body and touch the trophy, thus returning to Hogwarts.

Once Harry returns, he is weak and shaken. Moody carries him into the castle, where Moody reveals that he is in fact a Death Eater, and that he was responsible for placing Harry's name in the Goblet and for turning the trophy into a portkey. Moody also informs Harry that Karkaroff felt his Dark Mark burn and then fled that night. Moody prepares to kill Harry when Dumbledore and other teachers burst into the room, stunning Moody and saving Harry. Dumbledore explains to Harry that Moody's body is a disguised version of Mr. Crouch's son, the young Barty, and that he has made the switch by drinking Polyjuice potion every hour. After some time, the potion wears off and Harry recognizes Barty Crouch. Snape gives Crouch truth serum, and Crouch explains how his father smuggled him out of prison and allowed him to live under an Invisibility cloak, guarded by Winky; and how Bertha Jorkins discovered him and ultimately was relieved of his information by Voldemort, who returned to find young Crouch. He also says that he killed his father, and that he was hoping to bring Voldemort back into power by bringing Harry to him. Then Dumbledore takes Harry into his own office, where he asks Harry to explain what he saw in the graveyard to him and to Sirius, who had arrived. After listening to Harry, Dumbledore explains that the wands of Harry and Voldemort are made of feathers from the same phoenix, so one was forced to regurgitate its spells when the two wants met.

Harry is sent to bed, and in the night he is awakened by an argument between Cornelius Fudge and Dumbledore, in which Dumbledore tries unsuccessfully to persuade Fudge to take precautions against Voldemort's new power. Fudge refuses to believe that this is possible. He gives Harry the tournament prize money and leaves huffily. Soon the term ends, and at the final dinner Dumbledore makes a speech telling everyone how Cedric was murdered by Voldemort, and how the future looks bleak and would require them to join together. On the train ride back to London, Hermione shows Harry and Ron a beetle in a jar—Rita Skeeter's animagus form—that she caught and warned not to write any more untrue things. As the students leave the train, Harry gives his gold to the Weasley twins to help start their practical joke company, and he asks that they use some of it to buy Ron a new pair of dress robes. Harry returns to the Dursleys for the summer

[بحرينية أمورة]

خيوو بغيت حق فيز 213

 

مقدمه وعرض وخاتمه ومراجع

 

 

ويكووووووون في صفحتين

 

 

[جرح انسانه]

خيوو بغيت حق فيز 213

 

مقدمه وعرض وخاتمه ومراجع

 

 

ويكووووووون في صفحتين

 

 

تفضلي

 

المكثفات الكهربائية

المقدمة :

 

المكثف جهاز علمي يستخدم في مجال الفيزياء و بعض المجالات العلمية و منه انواع كثيرة كالهوائي و البلاستيكي و ميكا و الكثير من الانواع الاخرى التي تخدمنا في الجانب العلمي , متعدد الاستخدامات و له عوامل تؤثر على سعته .

 

العرض :

 

المكثف الكهربي عبارة عن لوحين من مادة موصلة بينهما مادة عازلة ، ويتحدد نوع المكثف على حسب المادة العازلة المستخدمة في صناعته، فإذا كانت المادة العازلة الموجودة بين لوحي المكثف هي الهواء فيطلق على المكثف في هذه الحالة اسم المكثف الهوائي، وإذا كانت مصنوعة من مادة البلاستيك سمي مكثف بلاستيك، وإذا كانت المادة العازلة من الميكا أطلق على المكثف اسم مكثف ميكا وإذا كانت المادة العازلة من السيراميك أطلق على المكثف اسم المكثف السيراميك، أما إذا استخدم محلول كيماوي كمادة عازلة بين لوحي المكثف أطلق على المكثف اسم المكثف الكيماوي أو الالكترولتي.

 

السعة:

تعرف قدرة المكثف على تخزين الشحنة الكهربية بالسعة الكهربية أو السعة ووحدة قياسها الفاراد، وتحسب قيمة سعة المكثف كالآتي:

نستنتج من هذا القانون أن اختيار قيمة المكثف في الدائرة الإلكترونية تتحدد بعاملين أساسيين هما سعة المكثف، وقيمة فرق الجهد المطبق على طرفيه، ووحدة قياس سعة الفاراد يمكن تقسيمها إلى وحدات أصغر

 

العوامل المؤثرة على سعة المكثف:

 

يوجد ثلاثة عوامل أساسية تؤثر على سعة المكثف بصورة مباشرة وهذه العوامل هي:

 

أ-المساحة السطحية لألواح المكثف (a):

إن سعة المكثف تتناسب طرديا مع المساحة السطحية للألواح، فإذا زادت مساحة سطح اللوح زادت سعة المكثف وذلك لزيادة استيعابه للشحنات الكهربائية، وبالعكس تقل سعة المكثف كلما قلت هذه المساحة.

ب- المسافة بين الألواح (d):

تقل السعة عندما تزداد المسافة بين الألواح وتزداد كلما قلت تلك المسافة أي أنه يوجد تناسب عكسي بين سعة المكثف والمساحة بين ألواحه.

ج- الوسط العازل (المادة العازلة) ε:

تتغير سعة المكثف بتغير المادة العازلة بين الألواح ويعتبر الهواء الوحدة الأساسية لمقارنة قابلية عزل المواد الأخرى المستعملة في صناعة المكثفات.

 

يوجد لكل مادة ثابت عزل يطلق عليه ابسلونε

المفاعلة (مقاومة المكثف الأومية):

 

المكثف الكهربي له مقاومة أوميةXc (لأنها تقاس بوحدة الأوم) تتغير مع التردد(F) وتتناسب عكسيا مع كل من السعةC والترددF ، في حالة التيار المستمر تكون قيمة الترددF تساوي (صفر)، وتكون بالتالي قيمة مقاومة المكثف الأوميةXc كبيرة جدا (ما لا نهاية) وبذلك فإن المكثف يمنع مرور التيار المستمر في الدائرة، بينما يمرر التيار المتغير وهذه الخاصية تعد أهم وظائف استعمالات المكثف في الدائرة الإلكترونية.

 

توصيل المكثفات على التوازي:

توصل المكثفات على التوازي للحصول على سعة كلية كبيرة تساوي مجموع سعة المكثفات المتصلة على التوازي

 

المفاعلة (مقاومة المكثف الأومية):

المكثف الكهربي له مقاومة أوميةXc (لأنها تقاس بوحدة الأوم) تتغير مع التردد(F) وتتناسب عكسيا مع كل من السعةC والترددF

في حالة التيار المستمر تكون قيمة الترددF تساوي (صفر)، وتكون بالتالي قيمة مقاومة المكثف الأوميةXc كبيرة جدا (ما لا نهاية) وبذلك فإن المكثف يمنع مرور التيار المستمر في الدائرة، بينما يمرر التيار المتغير وهذه الخاصية تعد أهم وظائف استعمالات المكثف في الدائرة الإلكترونية.

 

توصيل المكثفات على التوازي:

توصل المكثفات على التوازي للحصول على سعة كلية كبيرة تساوي مجموع سعة المكثفات المتصلة على التوازي

 

توصيل المكثفات على التوالي:

توصل المكثفات على التوالي للحصول على سعة كلية صغيرة أقل من أصغر سعة مكثف موجودة في الدائرة.

 

أنواع وأشكال المكثفات:

يطلق على المكثف ذي السعة الثابتة (المكثف الثابت)، أما المكثف الذي يمكن تغيير سعته (وذلك بتغيير المساحة المحصورة بين الألواح) فيطلق عليه اسم المكثف المتغير. يوجد أيضا نوع ثالث من المكثفات يمكن أن نتحكم في تغيير سعته، أو يترك دون تعديل لفترات زمنية طويلة ويطلق عليه اسم (مكثف تريمر) الذي قد نلجأ لضبط قيمته عند إجراء أعمال الصيانة والإصلاح في الدائرة الإلكترونية.

 

متسعة او مكثف Capacitor هي جهاز يخزن الطاقة في مجال كهربائي يتكون من زوج من الصفائح الموصلة يفصل بينهما عازل والتي تتجمع عليها شحنات متساوية في المقدار ولكن متعاكسة في الإشارة. والمتساعات المصنّعة لها صفائح رقيقة موصلة للكهرباء (تصنع من المعادن عادة) توضع فوق بعضها البعض أو تلف حول بعضها لتصغير حجم المواسع.

المتسعات او المكثفات انواع تعتمد على طريقة تصنيعها واستخدامها منها:- - المتسعات او المكثفات الورقية - المتسعات او المكثفات الكمياوية - المتسعات او المكثفات الهوائية

• تقاس سعة االمتسعات او المكثفات بوحدة القياس المايكرو فراد

• المتسعات تصنع لتعمل تحت جهد كهربائي مختلف Voltage من بضع عشرات من الفولتات كما في الدوائر الالكترونية و الكهربائية الى الاف من الالفولتات كما في شبكات القدرة الكهربائية

قوانين

سعة المواسع = الشحنة على المواسع ÷ فرق الجهد بين طرفي المواسع

حيث ان الشحنة على المواسع هي الشحنة على أحد الصفيحتين إذ ان الصفيحتين تحملان شحنات متساوية في المقدار ومتعاكسة في الإشارة .

السعة المكافئة موسعتين مربوطة على التوازي:

س (مكافئة)= س1 + س2

السعة المكافئة موسعتين مربوطة على التوالي:

1/س (مكافئة)= 1/س1 + 1/س2

المُكثِّف أداة تختزن الطاقة الكهربائية في شكل شحنات كهربائية. تُستخدم المكثفات بكثرة في الدوائر الكهربائية والإلكترونية. فعلى سبيل المثال، يستطيع المكثف أن ينظم سريان التيار المتناوب، كما يمكن أن يصد سريان التيار المستمر. وبإضافة أجهزة أخرى للمكثف، يمكن توليف أجهزة المذياع والتلفاز، بحيث تستقبل المحطات المختلفة. وقد بلغت المكثفات الحديثة المستعملة في الدوائر الإلكترونية المتكاملة حدًا من صغر الحجم بحيث لا يمكن مشاهدتها إلا بالمجهر. وتستخدم هذه الدوائر في الحاسبات، والساعات الرقمية، والحواسيب المصغرة، وأنواع أخرى كثيرة من الأجهزة.

 

طريقة عمل المكثف.

يتكون المكثف من لوحين فلزيين تفصل بينهما مادة عازلة تسمى العازل الكهربائي. وفي معظم الحالات يوصل المكثف بمصدر للكهرباء مثل بطارية. وعندما تنساب الشحنة الكهربائية من أحد لوحي المكثف إلى اللوح الآخر، فإن كلا اللوحين يكتسبان شحنة كهربائية، حيث يكتسب أحد اللوحين شحنة موجبة والآخر شحنة سالبة. وعندئذ يتكون بين اللوحين فرق جهد في القدرة يسمى الجهد. وإذا فصل اللوحان عن مصدر القدرة الكهربائية، ووصِّل السلكان ببعضهما، فإن الشحنة الكهربائية تنساب من اللوحين.

 

وتسمى قدرة المكثف على تخزين الطاقة الكهربائية السعة. وللمكثف ذي اللوحين الكبيرين والعازل الرقيق سعة أكبر من تلك التي يتصف بها المكثف ذو اللوحين الصغيرين والعازل العريض. وتتوقف السعة أيضًا على مستوى جودة العازل الكهربائي.

 

 

أنواع المكثفات.

تصنع المكثفات من مواد مختلفة وفي أشكال وأحجام مختلفة، وتصنف ـ وفقًا لنوع المادة المستعملة عازلاً كهربائيًا. والمواد شائعة الاستعمال تشمل الخزف والزجاج والمايكا واللدائن والورق المبلل بالزيت. وعلى سبيل المثال هنالك نوع من المكثفات يتكون من طبقة رقيقة من عازل بلاستيكي محصور بين شريطين طويلين من رقائق الألومنيوم. والبلاستيك هو العازل الكهربائي. ويطوى البلاستيك والملف لتقليل الفراغ.

 

تصمم بعض المكثفات لأغراض خاصة.

وتستخدم المكثفات الإلكتروليتية كثيرًا في الصناعة، خاصة لدى شركات توليد الكهرباء. ويوضع بين ألواح هذه المكثفات صحيفة رقيقة من الورق سبق أن غمرت في محلول إلكتروليتي، وهو محلول موصل للكهرباء ويسبب تكوين عازل كهربائي على سطح أحد الألواح.

 

وتستعمل المكثفات ذات العازل الزيتي في الأدوات التي تتطلب جهدًا عاليًا. ويتكون العازل من زيت معدني يوضع بين صفوف من الألواح.

 

وتستعمل مكثفات التوليف لانتقاء محطات الإذاعة والتلفاز المطلوبة. وهنالك نوع من مكثفات التوليف في أجهزة المذياع يستخدم الهواء عازلاً بين مجموعتين من الألواح. ويمكن تحريك إحدى المجموعتين ، بحيث يتغير حجم الهواء الفاصل بينهما، وهكذا تتغير السعة.

 

الخاتمة :

 

المكثف جهاز متعدد الاستخدامات منها امرار التيار و منع مروره في الدائرة الالكترونية , كما انه يستخدم للشحن و التفريغ كتخزين الشحنات الكهربية و يستخدم للحصول على اشكال موجات متنوعة و من هنا تظهر أهميته و فائدته التي يجهلها الكثير منا .

 

 

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