Kim loại dùng làm catod của một tế bào quang điện có công thoát electron 2,27 eV. Giới hạn quang điện λ0 của kim loại này:

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Một số câu hỏi khác có thể bạn quan tâm.

• The boy waved his hands to his mother, who was standing at the school gate, to _______ her attention.

• Cho hàm số với là tham số thực. Tìm tất cả các giá trị của để hàm số có điểm cực trị.  

• Lợn được nuôi chủ yếu ở
  
• Lựa chọn đáp án đúng để điền vào những chỗ trống dưới đây sao cho phù hợp.
  . . . . . . . . . . . . . . . . . . mới chỉ là khả năng của lao động.
  
• Read the passage carefully and choose the correct answers
  What picture do you have of the future? Will life in the future be better, worse or the same as now? What do you hope about the future?
  Futurologists predict that life will probably be very different in 2050 in all the fields, from entertainment to technology. First of all, it seems that TV channels will have disappeared. Instead, people will choose a program from a 'menu' and a computer will send the program directly to the television.
  Today, we can use the World Wide Web to read newspaper stories and see pictures on a computer thousands of kilometers away. By 2050, music, films, programs, newspapers and books will come to us by computer.
  In what concerns the environment, water will have become one of our most serious problems. In many places, agriculture is changing and farmers are growing fruit and vegetables to export.  This uses a lot of water. Demand for water will increase ten times between now and 2050 and there could be serious shortages. Some futurologists predict that water could be the cause of war if we don't act now.
  In transport, cars running on new, clean fuels will have computers to control the speed and there won't be any accidents. Today, many cars have computers that tell drivers exactly where they are. By 2050, the computer will control the car and drive it to your destination. On the other hand, space planes will take people halfway around the world in two hours. Nowadays, the United States Shuttle can go into space and land on Earth again. By 2050, space planes will fly all over the world and people will fly from Los Angeles to Tokyo in just two hours.
  In the domain of technology, robots will have replaced people in factories. Many factories already use robots. Big companies prefer robots - they do not ask for pay rises or go on strike, and they work 24 hours a day. By 2050, we will see robots everywhere - in factories, schools, offices, hospitals, shops and homes.
  Last but not least, medicine technology will have conquered many diseases. Today, there are electronic devices that connect directly to the brain to help people hear. By 2050, we will be able to help blind and deaf people see and hear again. Scientists have discovered how to control genes. They have already produced clones of animals. By 2050, scientists will be able to produce clones of people and decide how they look, how they behave and how much intelligence they have.
  (Source: Cambridge English for Schools by Andrew Littlejohn, Diana Hicks)
  Question. The word “This” in paragraph 3 refers to _________ .
  

• Trong các câu thành ngữ sau câu nào nói đến sự thay về lượng sẽ dẫn đến sự thay đổi về chất?

• Sản lượng lương thực của Trung Quốc cao nhất thế giới, nguyên nhân chủ yếu là do
  
• Tình yêu quê hương, đất nước và tinh thần sẵn sàng đem hết khả năng của mình phục vụ lợi ích của tổ quốc được gọi là
  
• Dùng một lò xo để treo vật có khối lượng 300g thì lò xo dãn ra 2 cm, nếu treo thêm một vật có khối lượng 150g vào thì lò xo dãn ra một đoạn là bao nhiêu ?
  

• If something _______ your attention or your eye, you notice it or become interested in it.