F5 phy question [復制鏈接]

Assume the resistance of the conducting wire and battery are both zero and an ideal voltmeter is used( i.e. Resistance of voltmeter= )

I1 = 3V
I2 = 0V ( Voltmeter drawn all current)

Potential Difference=3V

∴ A voltage of 3V can be measured.

is this correct??

or
I1 = I2 because current is constant in series circuit
voltmeter draw all p.d. instead ( as R=infinity)

I1 should be 0A <--- current should be in ampere unit

I2 = 0A also

since it is ideal voltmeter, so resistance of voltmeter = infinity



also the statement you mention, I1=I2 in series circuit

引用第1樓BVEsun於2009-11-20 11:27發表的“”:
I1 should be 0A <--- current should be in ampere unit
I2 = 0A also
since it is ideal voltmeter, so resistance of voltmeter = infinity
.......

Volt not current-.-

I1,2 都係 0A

i am using I1 I2 to indicate the two points

i want to find voltage not current

引用第4樓Grape於2009-11-20 17:37發表的“”:
[表情] [表情] [表情]
i am using I1 I2 to indicate the two points [表情]
i want to find voltage not current [表情]

all notation in Physics have special meaning

I is stand for current

please don't use your own notation or no others can understand the meaning

the p.d. can be anything you like

既然你話係ideal voltmeter




V=IR

As R=infinity

V=infinity or 0 (呢個有d tricky)


As V can't be infinity (impossible to have infinite energy --- V=Joule/C)



So V=0 ;

and I=0




qed

引用第7樓智者於2009-11-20 21:23發表的“”:
既然你話係ideal voltmeter
.......

"zero" x "infinty" should be = "undefined"...?

引用第8樓rBB於2009-11-20 21:44發表的“”:
"zero" x "infinty" should be = "undefined"...?

but "undefined" contradicts the real world (voltmeter 會跳下跳下?咁我地就唔會有能源危機了)

so in this case is 0

practically,

R=V/I;
R can not be infinity as I can not be 0 (minimum: 1 electron to pass through R)


no electron no energy


right?

引用第5樓BVEsun於2009-11-20 21:02發表的“”:
all notation in Physics have special meaning
I is stand for current
.......

sorry

引用第7樓智者於2009-11-20 21:23發表的“”:
既然你話係ideal voltmeter
.......

the conducting wire has no resistance


bcoz R=0, there is no energy dissipation


am i correct??

引用第9樓智者於2009-11-20 21:57發表的“”:
but "undefined" contradicts the real world (voltmeter 會跳下跳下?咁我地就唔會有能源危機了) [表情]
.......

Practically, the conducting wire and the battery bith have resistance.
∴It will draw current from the battery and there will be energy loss. It is mostly turned into heat energy by heating up the conducting wire.???


???

V=IR

R tends to infinity

I tends to 0


-------------------------------

V before entering voltmeter =3

V after leaving voltmeter tends to 0(R tends to infinity)

PD= 3

therefore a reading of 3V can be measured??

唔知岩定錯