Một nguồn sáng chỉ phát ra ánh sáng đơn sắc có tần số 7,5.1014 Hz, Biết số photon mà nguồn sáng phát ra trong mỗi giây là 2,01.1019 photon. Lấy h= 6,625.10-34 J.s; c=3.108 m/s. Công suất phát xạ của nguồn sáng xấp xỉ bằng:

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Một số câu hỏi khác có thể bạn quan tâm.

• Choose the best answer for the following sentence:

  Internet brings us too much information ____________ it makes us passive for we don't have to think much.
  
  

• Choose the word that has the underlined part pronounced differently from the rest: 

  make                 fame                 cake                  bad

• Choose the word that has the underlined part pronounced differently from the rest: 

  fat                     private                       cat                      mad

• Choose the word that has the underlined part pronounced differently from the rest: 

  spend                  send                      lend                   become

• Choose the best answer for the following sentence:

  Look! Someone ___________ the coffee on the keyboard.
  
  

• Choose a word that has different stress pattern:

  experience                 favourite                  subject                  primary

• Choose the best answer for the following sentence:

  Nghia: “Where _____________ born?”

  Ngoc: “In Kim Lien, Nam Dan”
  
  

• Choose a word that has different stress pattern:

  interview                   background                      scientific                      secondary

• Choose the best answer for the following sentence:

  He failed the exam to university last year. Since then he ______________ very hard
  the next entrance examination.
   

• Choose a word that has different stress pattern:

  education                 romantic                      conversation                      information