Calculate Voltage

[匿名]

2011-09-11 1:35 pm

A 9V battery with R = 100 Ohm is used to charge a 1.5V NiMH rechargeable battery with 2000mA short circuit current. If the charging current shall be 50mA, what resistor should be used.

Here is the circuit given by my teacher.

圖片參考：http://imgcld.yimg.com/8/n/HA00799676/o/701109110014313873456340.jpg
And here is another one he gave us( I think it is a simplified one)

圖片參考：http://imgcld.yimg.com/8/n/HA00799676/o/701109110014313873456351.jpg
Then this is the solution, but I don't understand why he calculated like this:

1.5V / 2000 = 0.75 Ohm

7.5/(100+ Rx) = 50mA

Rx = 50 ( He told us to solve for Rx, so I got 50 Ohm, but I don't know if it is right)

But I totally don't understand the steps. Please help me so I can understand. Greatly appreciated.

回答 (1)

用戶8430

2011-09-16 12:05 am

✔ 最佳答案

請問你要問的是你所寫的還是照圖計算?
因爲根據你寫的 :
A 9V battery with R = 100 Ohm is used to charge a 1.5V NiMH rechargeable battery with 2000mA short circuit current . If the charging current shall be 50mA, what resistor should be used.

1. 9V 電池的内部電阻100Ω
2. 1.5V NiMH 可充電電池如果短路有2000mA電流
3. 如果用9V 電池來對1.5V NiMH 可充電電池充電電流50mA, 你要知道需要串聯電阻是多少

1. 你需要先搵出 1.5V NiMH 内部電阻係幾多, R = V/I : 1.5/2 = 0.75Ω

2. 接下來 9V - 1.5V = 7.5V

3. 再下來 7.5V / 0.05A = 150Ω

4. 最後 150Ω - ( 100Ω + 0.75Ω ) = 49.25Ω

答案 = 49.25Ω

因爲

圖片參考：http://imgcld.yimg.com/8/n/HA00639401/o/701109110014313873456350.jpg

如果要根據你既圖來解答就問題不成立

圖片參考：http://imgcld.yimg.com/8/n/HA00639401/o/701109110014313873456362.jpg

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