Đoạn mạch xoay chiều không phân nhánh gồm cuộn dây thuần cảm và một tụ điện thì:

Đặt điện áp xoay chiều có giá trị hiệu dụng 200V và tần số không đổi vào hai đầu A và B của đoạn mạch mắc nối tiếp theo thứ tự gồm biến trở R, cuộn cảm thuần có độ tự cảm L và tụ điện có điện dung C thay đổi. Gọi N là điểm nối giữa cuộn cảm thuần và tụ điện. Các giá trị R, L, C hữu hạn và khác không. Với C = C₁ thì điện áp hiệu dụng giữa hai đầu biến trở R có giá trị không đổi và khác không khi thay đổi giá trị R của biến trở. Với C =  thì điện áp hiệu dụng giữa A và N bằng:

Cho đoạn mạch R, L, C mắc nối tiếp như hình vẽ. Điện áp tức thời giữa hai đầu đoạn mạch có biểu thức u = 60cos100πt (V). Biết rằng: U_AD= U_DB = 60 V, độ tự cảm của cuộn dây thuần cảm là L₁ = (H). Biểu thức của cường độ dòng điện chạy trong đoạn mạch là:

Một cuộn dây có độ tự cảm L = 0,32 (H). Tổng trở của cuộn cảm đó khi có một dòng điện xoay chiều có tần số 1000 (Hz) chạy qua là:

Trong một mạch R, L, C mắc nối tiếp với R = 10,0 (Ω), Z_L = 8,0 (Ω), Z_C = 6 (Ω); khi tần số là f thì tổng trở tương ứng với tần số đó là:

Máy biến thế được gọi là máy giảm thế khi:

** Cho mạch điện xoay chiều như hình bên. Đặt vào hai điểm A và B một hiệu điện thế xoay chiều u = 150sin100πt (V). Bỏ qua điện trở dây nối và điện trở khoá K. Biết rằng: khi K đóng các hiệu điện thế hiệu dụng U_AM = 35 (V), U_MN = 85 (V) và công suất tiêu thụ của cả mạch P = 37,5 (W). Khi K mở, các hiệu điện thế hiệu dụng U_AM và U_MN vẫn có giá trị như khi K đóng.

Giá trị của điện trở R tham gia trong mạch là:

Một vôn kế trong một mạch điện chỉ 50 (V) và một ampe kế mắc nối tiếp chỉ 5 (A). Công suất tiêu thụ trong mạch thì:

Tìm phát biểu đúng về công suất trung bình P tiêu thụ bởi mạch điện xoay chiều:

Người ta đặt một mạch điện trong một hộp đen có hai đầu dây nối ra ngoài. Biết rằng mạch điện chỉ sử dụng một trong 3 linh kiện điện trở thuần R, tụ điện C, cuộn cảm L thuần cảm hoặc gồm 2 trong 3 linh kiện trên mắc nối tiếp. Bằng thực nghiệm thấy rằng cường độ dòng điện trong mạch cùng pha với điện áp đặt vào hai đầu mạch điện. Mạch điện được cấu tạo bởi:

Mạch chỉ có R nối tiếp L. Tăng tần số ω thì:

Một dòng điện 0,5 (A) chạy vào một nam châm điện có điện trở không đáng kể, khi nó nối với một nguồn điện xoay chiều 120V - 60Hz (cảm kháng) của nam châm là:

Kết luận nào sau đây là sai khi so sánh máy phát điện xoay chiều ba pha và máy phát điện xoay chiều một pha?

Đơn vị của từ thông là vêbe (Wb), với một vêbe bằng:

Gọi I là cường độ dòng điện không đổi chạy qua một điện trở thuần R, cường độ dòng điện này bằng giá trị hiệu dụng của một dòng điện xoay chiều. Nếu cho cả hai dòng điện đó lần lượt đi qua cùng một điện trở trong cùng một khoảng thời gian đủ dài thì:

Cho đoạn mạch xoay chiều RLC mắc nối tiếp, giá trị điện dung C có thể thay đổi được. Biết điện áp giữa hai đầu mạch AB là u = Ucos(ωt)(V). Thay đổi C thì thấy có hai giá trị của C là C₁ =  F và C₂ = F làm cho cường độ dòng điện i₁ và i₂ đều lệch pha với u một góc  rad. Giá trị của R và L là:

Cho một tụ điện có điện dung C =  F mắc nối tiếp với một ống dây. Biết điện áp giữa hai đầu đoạn mạch trễ pha  so với cường độ dòng điện. Hỏi ống dây có đặc điểm gì:

Đoạn mạch xoay chiều không phân nhánh gồm cuộn dây thuần cảm và một tụ điện thì:

Cho đoạn mạch RLC mắc nối tiếp. Đặt một điện áp xoay chiều u = Ucos(ωt) (V) vào hai đầu đoạn mạch và thay đổi tần số f để điện áp trên hai đầu cuộn cảm đạt giá trị cực đại. Giá trị điện áp cực đại trên hai đầu cuộn cảm bằng:

Một đoạn mạch điện xoay chiều như hình bên. Hộp đen X₁, X₂ gồm một linh kiện trong số các linh kiện R, L, C. Khi đặt điện áp xoay chiều vào hai đầu A và B thì điện áp hai đầu hộp đen X₁ lệch pha so với điện áp hai đầu hộp đen X₂ một góc φ = . Khi đặt điện áp một chiều vào hai đầu A và B thì ampe kế chỉ số không. Hộp X₁ và X₂ chứa các phần tử lần lượt là:

Một mạch điện xoay chiều gồm R = 30 (Ω) mắc nối tiếp với cuộn dây L (thuần cảm). Điện áp ở giữa hai đầu đoạn mạch u = 120cos100πt (V). Biết U_L = 60 (V). Cảm kháng Z_L là:

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

The concept of obtaining fresh water from iceberg that are towed to populated areas and arid regions of the world was once treated as a joke more appropriate to cartoons than real life. But now it is being considered quite seriously by many nations, especially since scientists have warned that the human race will outgrow its fresh water supply faster than it runs out of food. Glaciers are a possible source of fresh water that have been overlooked until recently. Three-quarters of the Earth's fresh water supply is still tied up in glacial ice, a reservoir of untapped fresh water so immense that it could sustain all the rivers of the world for 1,000 years. Floating on the oceans every year are 7,659 trillion metric tons of ice encased in 10,000 icebergs that break away from the polar ice caps, more than ninety percent of them from Antarctica. Huge glaciers that stretch over the shallow continental shelf give birth to icebergs throughout the year. Icebergs are not like sea ice, which is formed when the sea itself freezes; rather, they are formed entirely on land, breaking off when glaciers spread over the sea. As they drift away from the polar region, icebergs sometimes move mysteriously in a direction opposite to the wind, pulled by subsurface currents. Because they melt more slowly than smaller pieces of ice, icebergs have been known to drift as far north as 35 degrees south of the equator in the Atlantic Ocean. To corral them and steer them to parts of the world where they are needed would not be too difficult. The difficulty arises in other technical matters, such as tile prevention of rapid melting in warmer climates and the funneling of fresh water to shore in great volume. But even if the icebergs lost half of their volume in towing, the water they could provide would be far cheaper than that produced by desalination, or removing salt from water.

Question 31: According to the author, most of the world’s fresh water is to be found in_______         

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

The concept of obtaining fresh water from iceberg that are towed to populated areas and arid regions of the world was once treated as a joke more appropriate to cartoons than real life. But now it is being considered quite seriously by many nations, especially since scientists have warned that the human race will outgrow its fresh water supply faster than it runs out of food. Glaciers are a possible source of fresh water that have been overlooked until recently. Three-quarters of the Earth's fresh water supply is still tied up in glacial ice, a reservoir of untapped fresh water so immense that it could sustain all the rivers of the world for 1,000 years. Floating on the oceans every year are 7,659 trillion metric tons of ice encased in 10,000 icebergs that break away from the polar ice caps, more than ninety percent of them from Antarctica. Huge glaciers that stretch over the shallow continental shelf give birth to icebergs throughout the year. Icebergs are not like sea ice, which is formed when the sea itself freezes; rather, they are formed entirely on land, breaking off when glaciers spread over the sea. As they drift away from the polar region, icebergs sometimes move mysteriously in a direction opposite to the wind, pulled by subsurface currents. Because they melt more slowly than smaller pieces of ice, icebergs have been known to drift as far north as 35 degrees south of the equator in the Atlantic Ocean. To corral them and steer them to parts of the world where they are needed would not be too difficult. The difficulty arises in other technical matters, such as tile prevention of rapid melting in warmer climates and the funneling of fresh water to shore in great volume. But even if the icebergs lost half of their volume in towing, the water they could provide would be far cheaper than that produced by desalination, or removing salt from water.

Question 30: The word “appropriate” in paragraph 1 is closest in meaning to_______          

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

The concept of obtaining fresh water from iceberg that are towed to populated areas and arid regions of the world was once treated as a joke more appropriate to cartoons than real life. But now it is being considered quite seriously by many nations, especially since scientists have warned that the human race will outgrow its fresh water supply faster than it runs out of food. Glaciers are a possible source of fresh water that have been overlooked until recently. Three-quarters of the Earth's fresh water supply is still tied up in glacial ice, a reservoir of untapped fresh water so immense that it could sustain all the rivers of the world for 1,000 years. Floating on the oceans every year are 7,659 trillion metric tons of ice encased in 10,000 icebergs that break away from the polar ice caps, more than ninety percent of them from Antarctica. Huge glaciers that stretch over the shallow continental shelf give birth to icebergs throughout the year. Icebergs are not like sea ice, which is formed when the sea itself freezes; rather, they are formed entirely on land, breaking off when glaciers spread over the sea. As they drift away from the polar region, icebergs sometimes move mysteriously in a direction opposite to the wind, pulled by subsurface currents. Because they melt more slowly than smaller pieces of ice, icebergs have been known to drift as far north as 35 degrees south of the equator in the Atlantic Ocean. To corral them and steer them to parts of the world where they are needed would not be too difficult. The difficulty arises in other technical matters, such as tile prevention of rapid melting in warmer climates and the funneling of fresh water to shore in great volume. But even if the icebergs lost half of their volume in towing, the water they could provide would be far cheaper than that produced by desalination, or removing salt from water.

Question 33: How are icebergs formed?         

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

The concept of obtaining fresh water from iceberg that are towed to populated areas and arid regions of the world was once treated as a joke more appropriate to cartoons than real life. But now it is being considered quite seriously by many nations, especially since scientists have warned that the human race will outgrow its fresh water supply faster than it runs out of food. Glaciers are a possible source of fresh water that have been overlooked until recently. Three-quarters of the Earth's fresh water supply is still tied up in glacial ice, a reservoir of untapped fresh water so immense that it could sustain all the rivers of the world for 1,000 years. Floating on the oceans every year are 7,659 trillion metric tons of ice encased in 10,000 icebergs that break away from the polar ice caps, more than ninety percent of them from Antarctica. Huge glaciers that stretch over the shallow continental shelf give birth to icebergs throughout the year. Icebergs are not like sea ice, which is formed when the sea itself freezes; rather, they are formed entirely on land, breaking off when glaciers spread over the sea. As they drift away from the polar region, icebergs sometimes move mysteriously in a direction opposite to the wind, pulled by subsurface currents. Because they melt more slowly than smaller pieces of ice, icebergs have been known to drift as far north as 35 degrees south of the equator in the Atlantic Ocean. To corral them and steer them to parts of the world where they are needed would not be too difficult. The difficulty arises in other technical matters, such as tile prevention of rapid melting in warmer climates and the funneling of fresh water to shore in great volume. But even if the icebergs lost half of their volume in towing, the water they could provide would be far cheaper than that produced by desalination, or removing salt from water.

Question 32: The word “currents” in paragraph 3 is closest in meaning to_________         

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

The concept of obtaining fresh water from iceberg that are towed to populated areas and arid regions of the world was once treated as a joke more appropriate to cartoons than real life. But now it is being considered quite seriously by many nations, especially since scientists have warned that the human race will outgrow its fresh water supply faster than it runs out of food. Glaciers are a possible source of fresh water that have been overlooked until recently. Three-quarters of the Earth's fresh water supply is still tied up in glacial ice, a reservoir of untapped fresh water so immense that it could sustain all the rivers of the world for 1,000 years. Floating on the oceans every year are 7,659 trillion metric tons of ice encased in 10,000 icebergs that break away from the polar ice caps, more than ninety percent of them from Antarctica. Huge glaciers that stretch over the shallow continental shelf give birth to icebergs throughout the year. Icebergs are not like sea ice, which is formed when the sea itself freezes; rather, they are formed entirely on land, breaking off when glaciers spread over the sea. As they drift away from the polar region, icebergs sometimes move mysteriously in a direction opposite to the wind, pulled by subsurface currents. Because they melt more slowly than smaller pieces of ice, icebergs have been known to drift as far north as 35 degrees south of the equator in the Atlantic Ocean. To corral them and steer them to parts of the world where they are needed would not be too difficult. The difficulty arises in other technical matters, such as tile prevention of rapid melting in warmer climates and the funneling of fresh water to shore in great volume. But even if the icebergs lost half of their volume in towing, the water they could provide would be far cheaper than that produced by desalination, or removing salt from water.

Question 29: What is the main topic of the passage?         

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

The concept of obtaining fresh water from iceberg that are towed to populated areas and arid regions of the world was once treated as a joke more appropriate to cartoons than real life. But now it is being considered quite seriously by many nations, especially since scientists have warned that the human race will outgrow its fresh water supply faster than it runs out of food. Glaciers are a possible source of fresh water that have been overlooked until recently. Three-quarters of the Earth's fresh water supply is still tied up in glacial ice, a reservoir of untapped fresh water so immense that it could sustain all the rivers of the world for 1,000 years. Floating on the oceans every year are 7,659 trillion metric tons of ice encased in 10,000 icebergs that break away from the polar ice caps, more than ninety percent of them from Antarctica. Huge glaciers that stretch over the shallow continental shelf give birth to icebergs throughout the year. Icebergs are not like sea ice, which is formed when the sea itself freezes; rather, they are formed entirely on land, breaking off when glaciers spread over the sea. As they drift away from the polar region, icebergs sometimes move mysteriously in a direction opposite to the wind, pulled by subsurface currents. Because they melt more slowly than smaller pieces of ice, icebergs have been known to drift as far north as 35 degrees south of the equator in the Atlantic Ocean. To corral them and steer them to parts of the world where they are needed would not be too difficult. The difficulty arises in other technical matters, such as tile prevention of rapid melting in warmer climates and the funneling of fresh water to shore in great volume. But even if the icebergs lost half of their volume in towing, the water they could provide would be far cheaper than that produced by desalination, or removing salt from water.

Question 35: The word “that” in the last paragraph refers to______         

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

The concept of obtaining fresh water from iceberg that are towed to populated areas and arid regions of the world was once treated as a joke more appropriate to cartoons than real life. But now it is being considered quite seriously by many nations, especially since scientists have warned that the human race will outgrow its fresh water supply faster than it runs out of food. Glaciers are a possible source of fresh water that have been overlooked until recently. Three-quarters of the Earth's fresh water supply is still tied up in glacial ice, a reservoir of untapped fresh water so immense that it could sustain all the rivers of the world for 1,000 years. Floating on the oceans every year are 7,659 trillion metric tons of ice encased in 10,000 icebergs that break away from the polar ice caps, more than ninety percent of them from Antarctica. Huge glaciers that stretch over the shallow continental shelf give birth to icebergs throughout the year. Icebergs are not like sea ice, which is formed when the sea itself freezes; rather, they are formed entirely on land, breaking off when glaciers spread over the sea. As they drift away from the polar region, icebergs sometimes move mysteriously in a direction opposite to the wind, pulled by subsurface currents. Because they melt more slowly than smaller pieces of ice, icebergs have been known to drift as far north as 35 degrees south of the equator in the Atlantic Ocean. To corral them and steer them to parts of the world where they are needed would not be too difficult. The difficulty arises in other technical matters, such as tile prevention of rapid melting in warmer climates and the funneling of fresh water to shore in great volume. But even if the icebergs lost half of their volume in towing, the water they could provide would be far cheaper than that produced by desalination, or removing salt from water.

Question 34: With which of the following ideas would the author be likely to agree?            

The three phases of human memory are the sensory memory, the short-term memory, and the long-term memory. This devision of the memory into phases is based on the length of time of the memory.

Sensory memory is instantaneous memory. It is an image or memory that enters your mind only for a short period of time; it comes and goes in under a second. The memory will not last longer than that unless the information enters the short-term memory.

Information can be held in the short-term memory for about twenty seconds or as long as you are actively using it. If you repeat a fact to yourself, that fact will stay in your short-term memory as long as you keep repeating it. Once you stop repeating it, either it is forgotten or it moves into long term memory.

Long-term memory is the huge memory tank that can hold ideas and images for years and years. Information can be added to your long-term memory when you actively try to put it there through memorization or when an idea or image enters your mind on its own.

Question: The expression “is based on” in the first paragraph could be best replaced by…………….  

The three phases of human memory are the sensory memory, the short-term memory, and the long-term memory. This devision of the memory into phases is based on the length of time of the memory.

Sensory memory is instantaneous memory. It is an image or memory that enters your mind only for a short period of time; it comes and goes in under a second. The memory will not last longer than that unless the information enters the short-term memory.

Information can be held in the short-term memory for about twenty seconds or as long as you are actively using it. If you repeat a fact to yourself, that fact will stay in your short-term memory as long as you keep repeating it. Once you stop repeating it, either it is forgotten or it moves into long term memory.

Long-term memory is the huge memory tank that can hold ideas and images for years and years. Information can be added to your long-term memory when you actively try to put it there through memorization or when an idea or image enters your mind on its own.

Question: The three phases of memory discussed in the pasage are differentiated according to…………….   

The three phases of human memory are the sensory memory, the short-term memory, and the long-term memory. This devision of the memory into phases is based on the length of time of the memory.

Sensory memory is instantaneous memory. It is an image or memory that enters your mind only for a short period of time; it comes and goes in under a second. The memory will not last longer than that unless the information enters the short-term memory.

Information can be held in the short-term memory for about twenty seconds or as long as you are actively using it. If you repeat a fact to yourself, that fact will stay in your short-term memory as long as you keep repeating it. Once you stop repeating it, either it is forgotten or it moves into long term memory.

Long-term memory is the huge memory tank that can hold ideas and images for years and years. Information can be added to your long-term memory when you actively try to put it there through memorization or when an idea or image enters your mind on its own.

Question: The best title for this pasage would be…………………….