Cuộn dây của một biến trở con chạy được làm bằng hợp kim Nikêlin có điện trở suất 0,40.10⁻⁶ Ω.m, có tiết diện đều là 0,60 mm² và gồm 500 vòng quấn quanh lõi sứ trụ tròn đường kính 4cm. a. Tính điện trở lớn nhất của biến trở này. b. Hiệu điện thế lớn nhất được phép đặt lên hai đầu cuộn dây của biến trở là 67V. Hỏi biến trở này chịu được dòng điện có cường độ lớn nhất là bao nhiêu?

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1. It is necessary that the mother ______ by breast milk. (feed her baby up / feeds her baby up / bed her baby up / feeds up her baby) 2. Maria is studying laws, ______? (isn’t Maria / is Maria / isn’t she / wasn’t she) 3. Would you mind ______ your pet snake somewhere else? (put / putting / to put / puts) 4. ______ the manager is out today, I’ll sign the letter. (Because / If / Because of / But) 5. My leg was hurting. I ______ walk. (could hardly / can hardly / could hard / can hard) 6. The driver was ______. (serious injured / injure seriously / seriously injured / injured seriously) 7. You haven’t written to her ______, have you? (recently / never / late / recent) 8. The boy likes ______ games but hates ______ his lessons. (play – study / playing – study / play – studying / playing – studying) 9. I’ve given your old jacket away ______ it was too tight for you. (because of / if / because / and) 10. Our holiday was too short. The time ______. (passed quick / quick passed / passed quickly / quickly passes) 11. You can’t stop me ______ what I want. (doing / to do / do / that I do) 12. Help me, ______? (will you / won’t you / do you / don’t you) 13. I like Cathy. She ______. (works very fastly / works very fast / work very fastly / working very fast) 14. I’m absolutely sure I locked the door. I clearly remember ______ it. (to lock / locking / lock / locked) 15. If you press that button, the alarm ______. (will ring / ring / ringing / would ring) 16. When I arrived, he was trying ______ it, but there was something wrong with the engine. (to start / stated / starting / start) 17. Bin ______ a novel, hasn’t he? (write / has written / wrote / will write) 18. If he likes the house, ______ buy it? (would he / will he / did he / does he) 19. If he ______ all that, he will be ill. (ate / will eat / has eaten / eats) 20. It is very important that everybody ______ very carefully. (should listen / to listen / listen / will listen)

1. It is necessary that the mother ______ by breast milk. (feed her baby up / feeds her baby up / bed her baby up / feeds up her baby) 2. Maria is studying laws, ______? (isn’t Maria / is Maria / isn’t she / wasn’t she) 3. Would you mind ______ your pet snake somewhere else? (put / putting / to put / puts) 4. ______ the manager is out today, I’ll sign the letter. (Because / If / Because of / But) 5. My leg was hurting. I ______ walk. (could hardly / can hardly / could hard / can hard) 6. The driver was ______. (serious injured / injure seriously / seriously injured / injured seriously) 7. You haven’t written to her ______, have you? (recently / never / late / recent) 8. The boy likes ______ games but hates ______ his lessons. (play – study / playing – study / play – studying / playing – studying) 9. I’ve given your old jacket away ______ it was too tight for you. (because of / if / because / and) 10. Our holiday was too short. The time ______. (passed quick / quick passed / passed quickly / quickly passes) 11. You can’t stop me ______ what I want. (doing / to do / do / that I do) 12. Help me, ______? (will you / won’t you / do you / don’t you) 13. I like Cathy. She ______. (works very fastly / works very fast / work very fastly / working very fast) 14. I’m absolutely sure I locked the door. I clearly remember ______ it. (to lock / locking / lock / locked) 15. If you press that button, the alarm ______. (will ring / ring / ringing / would ring) 16. When I arrived, he was trying ______ it, but there was something wrong with the engine. (to start / stated / starting / start) 17. Bin ______ a novel, hasn’t he? (write / has written / wrote / will write) 18. If he likes the house, ______ buy it? (would he / will he / did he / does he) 19. If he ______ all that, he will be ill. (ate / will eat / has eaten / eats) 20. It is very important that everybody ______ very carefully. (should listen / to listen / listen / will listen)