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標題:
ce pp questions (urgent)
發問:
圖片參考：http://farm8.staticflickr.com/7023/6599882767_5f2e83a790_b.jpg35: Is it actually asking me the variation of voltage with time? (E is the ans) 37: Why is (3) incorrect? (the circled is the correct option)19: How to calculate? the model ans is 480J/kg, but my ans is:150*200*(1-20%)/0.02=1.2*10^6 J/kg. ... 顯示更多 圖片參考：http://farm8.staticflickr.com/7023/6599882767_5f2e83a790_b.jpg 35: Is it actually asking me the variation of voltage with time? (E is the ans) 37: Why is (3) incorrect? (the circled is the correct option) 19: How to calculate? the model ans is 480J/kg, but my ans is: 150*200*(1-20%)/0.02=1.2*10^6 J/kg. Is the model ans incorrect? If not, what's wrong with my approach? 20: Why is (3) incorrect? Although the temperature of the liquid is constant, but wouldn't stirring it improve the thermal contact of the liquid with the heater? 3: What is the device shown? What's its function? 4: 'Raising a heavy load with a screwjack has a higher efficiency then raising it without a screwjack.' Why is this incorrect? thanks
最佳解答:
35. Yes, a CRO measures voltage. The potential difference across RQ is applied to the y-plates of the CRO. 37 Statement (3) should be correct. A large area coil leads to a large change of magnetic flux when the coil rotates than that for a small area coil. 19. The "model" answer is probably wrong. 480 J/kg is a very low value. How would you expect the latent heat of vapourization to have such low value even taking account experimental uncertainties. You calculation is correct. 20. Stirring of the liquid before boiling would cause uniform mixing of the liquid, so as to achieve the same temperature throughout the liquid. But when the liquid reaches boiling point, all liquid is at the same temperature. Stirring thus achieve not much purpose. 3. It looks like a "relay", or a "reed switch". The "block" on the leftbranch is an electromagent. When current passes through it, it attracts the "switch" (which is an iron piece) on the right branch, thus closing the circuit connected to CD. 4. Clearly not correct. Raising it directly achieve almost 100% eficiency, but you need to exert an effort equals to the weight of the load. Using a screw-jack enables a smaller force (effort) to be applied, but there is a loss of efficiency (i.e. more work needs to be done as compared with the gain in potential energy of the lifting weight)
其他解答:
ce pp questions (urgent)
發問:
圖片參考：http://farm8.staticflickr.com/7023/6599882767_5f2e83a790_b.jpg35: Is it actually asking me the variation of voltage with time? (E is the ans) 37: Why is (3) incorrect? (the circled is the correct option)19: How to calculate? the model ans is 480J/kg, but my ans is:150*200*(1-20%)/0.02=1.2*10^6 J/kg. ... 顯示更多 圖片參考：http://farm8.staticflickr.com/7023/6599882767_5f2e83a790_b.jpg 35: Is it actually asking me the variation of voltage with time? (E is the ans) 37: Why is (3) incorrect? (the circled is the correct option) 19: How to calculate? the model ans is 480J/kg, but my ans is: 150*200*(1-20%)/0.02=1.2*10^6 J/kg. Is the model ans incorrect? If not, what's wrong with my approach? 20: Why is (3) incorrect? Although the temperature of the liquid is constant, but wouldn't stirring it improve the thermal contact of the liquid with the heater? 3: What is the device shown? What's its function? 4: 'Raising a heavy load with a screwjack has a higher efficiency then raising it without a screwjack.' Why is this incorrect? thanks
最佳解答:
35. Yes, a CRO measures voltage. The potential difference across RQ is applied to the y-plates of the CRO. 37 Statement (3) should be correct. A large area coil leads to a large change of magnetic flux when the coil rotates than that for a small area coil. 19. The "model" answer is probably wrong. 480 J/kg is a very low value. How would you expect the latent heat of vapourization to have such low value even taking account experimental uncertainties. You calculation is correct. 20. Stirring of the liquid before boiling would cause uniform mixing of the liquid, so as to achieve the same temperature throughout the liquid. But when the liquid reaches boiling point, all liquid is at the same temperature. Stirring thus achieve not much purpose. 3. It looks like a "relay", or a "reed switch". The "block" on the leftbranch is an electromagent. When current passes through it, it attracts the "switch" (which is an iron piece) on the right branch, thus closing the circuit connected to CD. 4. Clearly not correct. Raising it directly achieve almost 100% eficiency, but you need to exert an effort equals to the weight of the load. Using a screw-jack enables a smaller force (effort) to be applied, but there is a loss of efficiency (i.e. more work needs to be done as compared with the gain in potential energy of the lifting weight)
其他解答:
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