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急!!!徵求物理(電學)高手解答!!!(20點!!)

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下禮拜要考試 請大大幫我解答 過程詳細點 謝謝 (前四題在另一篇)5. A certain toaster has a heating element made of Nichrome wire. When the toaster is first connected to a 120-V source (and the wire is at a temperature of 20.0℃), the initial current is 1.80A. The current begins todecrease as the heating element warms up, however. When... 顯示更多 下禮拜要考試 請大大幫我解答 過程詳細點 謝謝 (前四題在另一篇) 5. A certain toaster has a heating element made of Nichrome wire. When the toaster is first connected to a 120-V source (and the wire is at a temperature of 20.0℃), the initial current is 1.80A. The current begins to decrease as the heating element warms up, however. When the toaster reaches its final operating temperature, the current drops to 1.53A. (a)Find the power delivered to the toaster when it is at its operating temperature. (b) What is the final temperature of the hrating element? 答案(a)184W(b) 461℃ 6. An electric car is designed to run off a bank of 12.0-V batteries with total energy storage of 2.00×10^7 J. (a)If the electric motor draws 8.00kW ,what is the current delivered to the motor? (b) If the electric motor draws as the car moves at a steady speed of 20.0 m/s, how far will the car travel before it is “out of juice”? 答案(a) 667A (b) 50km 更新: 很抱歉!!我忘記給鎳鉻絲的溫度係數 不過你設的沒有錯 經過你的算式我重新驗算發現 電阻還不夠精確 所以導致答案有些誤差 若電阻分別為66.66Ω及78.43Ω那麼答案就會一致了 很感謝你的詳解

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5-(a) 功率 P = V*I = 120*1.53 = 183.6 Watt 5-(b) 20 ℃ 時的電阻 R20 = 120/1.8 = 66.7Ω 通電至溫度穩定，假設是 T ℃，的電阻 RT = 120/1.53 = 78.4Ω 鎳鉻絲的溫度係數是 0.4*10^-3 (1/ ℃) 78.4 = 66.7 *(1 0.4*10^-3*(T-20)) 則 T = 459 ℃ 註：此答案有一點誤差，可能是我假設的溫度係數不夠精確所 致，照理溫度係數應該是題目裏要給定才能計算。 6-(a) P = V*I，所以 I = P/V = 8000/12 = 667 A 6-(b) W = P * t，所以 t = W/P = 2*10^7/8000 = 2500 秒 則總共行駛距離 S = 20*2500 = 50000 米 = 50 Km # 2007-05-21 20:23:46 補充： 上式 78.4 = 66.7 *(1 0.4*10^-3*(T-20)) 少打了一個 "+"，應該是 78.4 = 66.7 *(1+ 0.4*10^-3*(T-20)) 才對。

其他解答:

我知道 課本有這個公式 所以我知道你那裡是“+” 感謝你細心的提醒CF546184287637C5