Totall Resistance in circuit

總電阻係R1+R2||(Rb2+1Mohm)，其中+代表串連，||代表並連。

你電路圖並未提供電流數值，無法計算Rb2電阻值，請檢查錯漏。

但R2值細過1Mohm，並連後還低於300Kohm，大部份電流將會流過R2，Rb2基本上可以忽略，所以總電阻應該比900Kohm略小。

2011-10-09 17:44:53 補充：
你嘅R_total同我嘅總電阻似乎不同，我嘅總電阻係Vdc對地電阻。雖然你有提供電流值，但正如我所講r2電阻300k比1m細，用r=v/i計到都係300k，咁rb2+1m根本可有可無。

如果支probe係等如rb2+1m，咁rb2好明顯係probe內串聯電阻，如果以10:1計，1m電阻電壓降係0.3v，電流係0.3uA，rb2電壓降係2.7v，rb2=2.7V/0.3uA=9Mohm，所以支probe總電阻係10Mohm。

2011-10-09 17:45:04 補充：
你最後嗰句，Rb2 = R2 || R_total，你冇指出何處係R_total，無法計算，但事實上r2係並聯rb2+1m，所以估計r_total就係rb2+1m，由以上可知，rb2電阻極大，當r2<

2011-10-09 17:46:46 補充：
你最後嗰句，Rb2 = R2 || R_total，你冇指出何處係R_total，無法計算，但事實上r2係並聯rb2+1m，所以估計r_total就係rb2+1m，由以上可知，rb2電阻極大，當r2<

2011-10-09 17:47:15 補充：
當r2<

How can I find the total resistance of this circuit (R_total) and the resistance of resistor Rb2?
總電阻如以電池正負兩點計算，Rb2 是未知數，計算不了。
I don't understand why the answer is: Rb2 = R2 || R_total = 290k Ohm
看過補充的圖，接了 9V 電源，由 R1, R2 分壓，中心點為 3V ，那 Rb2 應該是非常大的電阻，大到可以忽略不計，否則這點會是低於 3V。

2011-10-10 10:31:59 補充：
故此 Rb2=R2 || R_total =290kOhm 是錯的

2011-10-10 10:58:41 補充：
示波器輸入內阻通常為 1MΩ，示波器探棒 1:1 是直接用了示波器內部阻抗，供一般的測量用，好處是高靈敏度，10:1 的探棒也就是提高了輸入阻抗至 10MΩ，這是為了測量微電流的電路而使用，否則當你接入探棒時，電路受影響訊號被拉低(並上了電阻)，出來的結果誤差就大了。這可能跟你的提問有些少關聯。

Well I voted for 003, so please tell me the reason why Rb2 = R2 || R_total = 290k Ohm.

Thanks

2011-10-09 14:17:21 補充：
I have a test 2 days later and the test might includes the concept of this type of question. So I will wait for your answer once you finish your business. Thanks a lot.

2011-10-09 14:59:24 補充：
parallel to.
Rb2 = R2 parallel to R_total

2011-10-10 11:00:58 補充：
So Rb2=R2 || R_total =290kOhm is impossible?

2011-10-10 11:58:00 補充：
I am going to ask my teacher directly. Since he gave me the solution, I bet he knows the best what he did. Thanks everyone.

Could you please visit this ignored question and vote for the correct answer? but do not confuse 003 with 004. 003 is me really. 004 is just my circuit pasting tool.

2011-10-09 11:07:17 補充：
I will imitate a mirror, will reflect what you act in front of me. you treat me good, I treat you good.

I may be able to tell you the reason why the answer is: Rb2 = R2 || R_total = 290k Ohm.

just wait and see.

2011-10-09 11:23:01 補充：
OH MY GOD ! I forgot the most important thing !
http://hk.knowledge.yahoo.com/question/question?qid=7011092900551

HELP ! I'm dying !

2011-10-09 14:10:15 補充：
Surely I will keep my promise. however, would you please give me two days to get you the answer? I'm buzying on my work.

2011-10-09 14:38:15 補充：
by the way, what is the meaning of the symbol " || " ?

2011-10-10 08:57:12 補充：
I,m so sorry Hold, I am sick with influenza and had a serious fever that can not give you a hand. I have sent mail to aa Knowledge Superior and Dr.Yau Lang Yau Tsang ask them for help, sorry for make you feel down.

2011-10-10 09:15:49 補充：
After input this sentence I will get backache also that I can not sit down to type any more. please forgive me, I owe you.

2011-10-10 11:34:44 補充：
I was thankful for aa ( 知識長 ) 's help. Amazingly, I make a full recovery from my illness.
Hold, are you sure there is nothing wrong with the given answer?
「Rb2 = R2 || R_total = 290k Ohm」
「The answer for R_total is 10 MOhm.」